MySQL高級（進階）SQL語句
目錄
一、實例准備--制表
1. 表1（商店區域表）
[root@localhost ~]# mysql
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.20-log Source distribution
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affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> use test;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql> create table location (region char(20),store_name char(20));
Query OK, 0 rows affected (0.01 sec)
mysql> insert into location values('North','Beijing');
Query OK, 1 row affected (0.00 sec)
mysql> insert into location values('Eaet','shanghai');
Query OK, 1 row affected (0.00 sec)
mysql> insert into location values('South','Guangzhou');
Query OK, 1 row affected (0.00 sec)
mysql> insert into location values('South','Shenzhen');
Query OK, 1 row affected (0.01 sec)
mysql> select * from location;
+--------+------------+
| region | store_name |
+--------+------------+
| North | Beijing |
| East | Shanghai |
| South | Guangzhou |
| South | Shenzhen |
+--------+------------+
4 rows in set (0.00 sec)
2. 表2（商店銷售表）
mysql> create table store_info (store_name char(20),sales int(10),date char(10));
Query OK, 0 rows affected (0.00 sec)
mysql> insert into store_info values('Guangzhou',1500,'2020-12-05');
Query OK, 1 row affected (0.00 sec)
mysql> insert into store_info values('Shenzhen',250,'2020-12-07');
Query OK, 1 row affected (0.00 sec)
mysql> insert into store_info values('Guangzhou',300,'2020-12-08');
Query OK, 1 row affected (0.00 sec)
mysql> insert into store_info values('Beijing',700,'2020-12-08');
Query OK, 1 row affected (0.00 sec)
mysql> select * from store_info;
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Guangzhou | 1500 | 2020-12-05 |
| Shenzhen | 250 | 2020-12-07 |
| Guangzhou | 300 | 2020-12-08 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
4 rows in set (0.00 sec)
3. 表3（城市表）
mysql> create table city(city_name char(20));
Query OK, 0 rows affected (0.00 sec)
mysql> insert into city values('beijing'),('nanjing'),('shanghai');
Query OK, 3 rows affected (0.01 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> insert into city values();
Query OK, 1 row affected (0.00 sec)
mysql> insert into city values();
Query OK, 1 row affected (0.00 sec)
mysql> insert into city values('');
Query OK, 1 row affected (0.00 sec)
mysql> select * from city;
+-----------+
| city_name |
+-----------+
| beijing |
| nanjing |
| shanghai |
| NULL |
| NULL |
| |
+-----------+
6 rows in set (0.00 sec)
4. 表4（total_sales）
mysql> create table total_sales (name char(20),sales int(5));
Query OK, 0 rows affected (0.01 sec)
mysql> insert into total_sales values('zhangsan',10);
Query OK, 1 row affected (0.00 sec)
mysql> insert into total_sales values('lisi',15);
Query OK, 1 row affected (0.01 sec)
mysql> insert into total_sales values('wangwu',20);
Query OK, 1 row affected (0.01 sec)
mysql> insert into total_sales values('zhaoliu',40);
Query OK, 1 row affected (0.00 sec)
mysql> insert into total_sales values('sunqi',50);
Query OK, 1 row affected (0.00 sec)
mysql> insert into total_sales values('zhouba',20);
Query OK, 1 row affected (0.01 sec)
mysql> insert into total_sales values('wujiu',30);
Query OK, 1 row affected (0.00 sec)
mysql> select * from total_sales;
+----------+-------+
| name | sales |
+----------+-------+
| zhangsan | 10 |
| lisi | 15 |
| wangwu | 20 |
| zhaoliu | 40 |
| sunqi | 50 |
| zhouba | 20 |
| wujiu | 30 |
+----------+-------+
7 rows in set (0.00 sec)
二、SQL語句
1. select
顯示表格中一個或數個欄位的所有資料
語法：select "欄位" from "表名";
mysql> select store_name from store_info;
+------------+
| store_name |
+------------+
| Guangzhou |
| Shenzhen |
| Guangzhou |
| Beijing |
+------------+
4 rows in set (0.00 sec)
2. distinct
不顯示重復的資料
語法：select dstinct "欄位" from "表名";
mysql> select distinct store_name from store_info;
+------------+
| store_name |
+------------+
| Guangzhou |
| Shenzhen |
| Beijing |
+------------+
3 rows in set (0.00 sec)
3. where
有條件查詢
語法：select "欄位" from "表名" where "條件";
mysql> select store_name from store_info where sales>1000;
+------------+
| store_name |
+------------+
| Guangzhou |
+------------+
1 row in set (0.00 sec)
4. and|or
且、或
語法：select "欄位" from "表名" where "條件1" {[and|or] “條件2”}...;
mysql> select store_name from store_info where sales>1000 or (sales<500 and sales>200);
+------------+
| store_name |
+------------+
| Guangzhou |
| Shenzhen |
| Guangzhou |
+------------+
3 rows in set (0.00 sec)
5. in
顯示已知的值的資料
語法：select "欄位" from "表名" where "欄位" in ("值1","值2",...);
mysql> select * from store_info where store_name in ('Beijing','Shenzhen');
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Shenzhen | 250 | 2020-12-07 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
2 rows in set (0.00 sec)
6. between
顯示兩個值范圍內的資料
語法：select "欄位" from "表名" where "欄位" between '值1' and '值2';
mysql> select * from store_info where date between '2020-12-06' and '2020-12-10';
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Shenzhen | 250 | 2020-12-07 |
| Guangzhou | 300 | 2020-12-08 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
3 rows in set (0.00 sec)
7. limit
（1）顯示前幾行內容
語法：select "欄位" from "表名" limit '行數';
mysql> select * from store_info limit 2;
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Guangzhou | 1500 | 2020-12-05 |
| Shenzhen | 250 | 2020-12-07 |
+------------+-------+------------+
2 rows in set (0.00 sec)
（2）顯示第幾行后的前幾行
語法：select "欄位" from "表名" limit "第幾行后,顯示行數";
mysql> select * from store_info limit 2,2;
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Guangzhou | 300 | 2020-12-08 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
2 rows in set (0.00 sec)
8. 通配符
通常通配符都是跟like一起使用的
| 常用通配符 | 說明 |
|---|---|
| % | 百分號表示零個、一個或多個字符 |
| _ | 下划線表示單個字符 |
例如：
'A-Z'
表示所有以'A'起頭，另一個任何值的字符，且以'Z'為結尾的字符串。例如，'ABZ'和'A2Z'都符合這一個模式，而'ABCZ'並不符合（因為A和Z之間有兩個字符，而不是一個字符）
'ABC%'
表示所有以'ABC'起頭的字符串。例如，'ABCD'和'ABCABC'都符合這個模式。
'%XYZ'
表示所有以'XYZ'結尾的字符串。例如，'WXYZ'和'ZZXYZ'都符合這個模式。
'%AN%'
表示所有含有'AN'這個模式的字符串。例如，'SHANGHAI'和'XIAN'都符合這個模式。
'_AN%'
表示第二個字母為'A'且第三個字母為'N'的字符串。例如，'HANGZHOU'和'LANZHOU'都符合這個模式，而'SHANGHAI'和'XIAN'則不符合這個模式。
9. like
匹配一個模式來搜查資料
語法：select "欄位" from “表名” where "欄位" like {模式};
mysql> select * from store_info where store_name like '%e%';
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Shenzhen | 250 | 2020-12-07 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
2 rows in set (0.00 sec)
10. order by
按關鍵字排序
語法：select "欄位" from “表名” [where "條件"] order by "欄位" [ASC,DESC];
ASC是按照升序進行排序的，是默認的排序方式。
DESC是按降序方式進行排序。
mysql> select store_name,sales,date from store_info order by sales desc;
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Guangzhou | 1500 | 2020-12-05 |
| Beijing | 700 | 2020-12-08 |
| Guangzhou | 300 | 2020-12-08 |
| Shenzhen | 250 | 2020-12-07 |
+------------+-------+------------+
4 rows in set (0.00 sec)
三、函數
1. 數學函數
| 常用的數學函數 | 說明 |
|---|---|
| abs(x) | 返回x的絕對值 |
| rand() | 返回0-1的隨機數 |
| mod(x,y) | 返回x除以y以后的余數 |
| power(x,y) | 返回x的y次方 |
| round(x) | 返回離x最近的整數，即四舍五入到個位 |
| round(x,y) | 返回x的y位小數且四舍五入后的值 |
| sqrt(x) | 返回x的平方根 |
| truncate(x,y) | 返回數字X截斷為y位小數的值 |
| ceil(x) | 返回大於或等於x的最小整數 |
| floor(x) | 返回小於或等於x的最大整數 |
| greatest(x1,x2...) | 返回集合中最大的值 |
| least(x1,x2...) | 返回集合中最小的值 |
（1）abs(x)
返回x的絕對值
mysql> select abs(-2.3);
+-----------+
| abs(-2.3) |
+-----------+
| 2.3 |
+-----------+
1 row in set (0.00 sec)
（2）rand()
返回0-1的隨機數
mysql> select rand();
+--------------------+
| rand() |
+--------------------+
| 0.1262695352791525 |
+--------------------+
1 row in set (0.00 sec)
（3）mod（x,y）
返回x除以y以后的余數
mysql> select mod(5,2);
+----------+
| mod(5,2) |
+----------+
| 1 |
+----------+
1 row in set (0.00 sec)
（4）power(x,y)
返回x的y次方
mysql> select power(2,8);
+------------+
| power(2,8) |
+------------+
| 256 |
+------------+
1 row in set (0.00 sec)
（5）round(x)
返回離x最近的整數,即四舍五入到個位
mysql> select round(3.1415);
+---------------+
| round(3.1415) |
+---------------+
| 3 |
+---------------+
1 row in set (0.00 sec)
mysql> select round(3.5415);
+---------------+
| round(3.5415) |
+---------------+
| 4 |
+---------------+
1 row in set (0.00 sec)
（6）round(x,y)
返回x的y位小數且四舍五入后的值
mysql> select round(3.1415,2);
+-----------------+
| round(3.1415,2) |
+-----------------+
| 3.14 |
+-----------------+
1 row in set (0.00 sec)
mysql> select round(3.1415,3);
+-----------------+
| round(3.1415,3) |
+-----------------+
| 3.142 |
+-----------------+
1 row in set (0.00 sec)
（7）sqrt(x)
返回x的平方根
mysql> select sqrt(9);
+---------+
| sqrt(9) |
+---------+
| 3 |
+---------+
1 row in set (0.00 sec)
mysql> select sqrt(8);
+--------------------+
| sqrt(8) |
+--------------------+
| 2.8284271247461903 |
+--------------------+
1 row in set (0.00 sec)
（8）truncate(x,y)
返回數字X截斷為y位小數的值
mysql> select truncate(3.1415,2);
+--------------------+
| truncate(3.1415,2) |
+--------------------+
| 3.14 |
+--------------------+
1 row in set (0.00 sec)
mysql> select truncate(3.1415,3);
+--------------------+
| truncate(3.1415,3) |
+--------------------+
| 3.141 |
+--------------------+
1 row in set (0.00 sec)
（9）ceil(x)
返回大於或等於x的最小整數
mysql> select ceil(3.1415);
+--------------+
| ceil(3.1415) |
+--------------+
| 4 |
+--------------+
1 row in set (0.00 sec)
（10）floor(x)
返回小於或等於x的最大整數
mysql> select floor(3.1415);
+---------------+
| floor(3.1415) |
+---------------+
| 3 |
+---------------+
1 row in set (0.00 sec)
（11）greatest(x1,x2...)
返回集合中最大的值
mysql> select greatest(3.1415,3,4,5.2);
+--------------------------+
| greatest(3.1415,3,4,5.2) |
+--------------------------+
| 5.2000 |
+--------------------------+
1 row in set (0.00 sec)
（12）least(x1,x2...)
返回集合中最小的值
mysql> select least(3.1415,3,4,5.2);
+-----------------------+
| least(3.1415,3,4,5.2) |
+-----------------------+
| 3.0000 |
+-----------------------+
1 row in set (0.00 sec)
2. 聚合函數
| 常用的聚合函數 | 說明 |
|---|---|
| avg() | 返回指定列的平均值 |
| count() | 返回指定列中非NULL值的個數 |
| min() | 返回指定列的最小值 |
| max() | 返回指定列的最大值 |
| sum() | 返回指定列的所有值之和 |
（1）avg()
返回指定列的平均值
mysql> select avg(sales) from store_info;
+------------+
| avg(sales) |
+------------+
| 687.5000 |
+------------+
1 row in set (0.00 sec)
（2）count()
- 返回指定列中非NULL值的個數
mysql> select count(store_name) from store_info;
+-------------------+
| count(store_name) |
+-------------------+
| 4 |
+-------------------+
1 row in set (0.00 sec)
- 返回指定列中非NULL值且去重的個數
mysql> select count(distinct store_name) from store_info;
+----------------------------+
| count(distinct store_name) |
+----------------------------+
| 3 |
+----------------------------+
1 row in set (0.00 sec)
- count()
count()包括了所有的列的行數，在統計結果的時候，不會忽略值為NULL的行
mysql> select count(*) from city;
+----------+
| count(*) |
+----------+
| 6 |
+----------+
1 row in set (0.00 sec)
- count("列名")
count("列名")只包括列名那一列的行數，在統計結果的時候，會忽略值為NULL的行
mysql> select count(city_name) from city;
+------------------+
| count(city_name) |
+------------------+
| 4 |
+------------------+
1 row in set (0.00 sec)
（3）min()
返回指定列的最小值
mysql> select min(sales) from store_info;
+------------+
| min(sales) |
+------------+
| 250 |
+------------+
1 row in set (0.01 sec)
（4）max()
返回指定列的最大值
mysql> select max(sales) from store_info;
+------------+
| max(sales) |
+------------+
| 1500 |
+------------+
1 row in set (0.00 sec)
（5）sum()
返回指定列的所有值之和
mysql> select sum(sales) from store_info;
+------------+
| sum(sales) |
+------------+
| 2750 |
+------------+
1 row in set (0.00 sec)
3. 字符串函數
| 常用的字符串函數 | 說明 |
|---|---|
| trim() | 返回去除指定格式的值 |
| concat(x,y) | 將提供的參數x和y拼接成一個字符串 |
| substr(x,y) | 獲取從字符串x中的第y個位置開始的字符串，跟substring()函數作用相同 |
| substr(x,y,z) | 獲取從字符串x中第y個位置開始長度為z的字符串 |
| length(x) | 返回字符串x的長度 |
| replace(x,y,z) | 將字符串z替代字符串x中的字符串y |
| upper(x) | 將字符串x的所有字母變成大寫字符 |
| lower(x) | 將字符串x的所有字母變成小寫字符 |
| left(x,y) | 返回字符串x的前y個字符 |
| right(x,y) | 返回字符串x的后y個字符 |
| reprat(x,y) | 將字符串x重復y次 |
| space(x) | 返回x個空格 |
| strcmp(x,y) | 比較x和y，返回的值可以為-1,0,1 |
| reverse(x) | 將字符串x反轉 |
（1）trim()
返回去除指定格式的值
語法：select trim([[位置] [要移除的字符串] from] 字符串);
[位置]：該值可以為leading（起頭），trailing（結尾），both（起頭及結尾）。缺省時為both。
[要移除的字符串]：從字串的起頭、結尾，或起頭即結尾移除的字符串。缺省時為空格。
mysql> select trim('g' from 'guangdong');
+----------------------------+
| trim('g' from 'guangdong') |
+----------------------------+
| uangdon |
+----------------------------+
1 row in set (0.00 sec)
mysql> select trim(leading 'g' from 'guangdong');
+------------------------------------+
| trim(leading 'g' from 'guangdong') |
+------------------------------------+
| uangdong |
+------------------------------------+
1 row in set (0.00 sec)
mysql> select trim(trailing 'g' from 'guangdong');
+-------------------------------------+
| trim(trailing 'g' from 'guangdong') |
+-------------------------------------+
| guangdon |
+-------------------------------------+
1 row in set (0.00 sec)
mysql> select trim(both 'g' from 'guangdong');
+---------------------------------+
| trim(both 'g' from 'guangdong') |
+---------------------------------+
| uangdon |
+---------------------------------+
1 row in set (0.00 sec)
（2）concat(x,y)
將提供的參數x和y拼接成一個字符串
mysql> select concat (region,' ',store_name) from location where store_name='Beeijing';
+--------------------------------+
| concat (region,' ',store_name) |
+--------------------------------+
| North Beijing |
+--------------------------------+
1 row in set (0.00 sec)
如sql_mode開啟了PIPES_AS_CONCAT（可使用"select @@SESSION.sql_mode;"或"select @@GLOBAL.sql_mode;"進行查看），"||"視為字符串的連接操作符而非或運算符，和字符串的拼接函數相類似，這和Oracle數據庫使用方法一樣。
mysql> select store_name || ' ' || sales from store_info where store_name='Guanngzhou';
+----------------------------+
| store_name || ' ' || sales |
+----------------------------+
| Guangzhou 1500 |
| Guangzhou 300 |
+----------------------------+
2 rows in set (0.00 sec)
（3）substr(x,y)
獲取從字符串x中的第y個位置開始的字符串，跟substring()函數作用相同
mysql> select substr(store_name,3) from location where store_name='Guangzhou';
+----------------------+
| substr(store_name,3) |
+----------------------+
| angzhou |
+----------------------+
1 row in set (0.00 sec)
（4）substr(x,y,z)
獲取從字符串x中第y個位置開始長度為z的字符串
mysql> select substr(store_name,3,4) from location where store_name='Guangzhou'';
+------------------------+
| substr(store_name,3,4) |
+------------------------+
| angz |
+------------------------+
1 row in set (0.00 sec)
（5）length(x)
返回字符串x的長度
mysql> select *,length(store_name) from location;
+--------+------------+--------------------+
| region | store_name | length(store_name) |
+--------+------------+--------------------+
| North | Beijing | 7 |
| East | Shanghai | 8 |
| South | Guangzhou | 9 |
| South | Shenzhen | 8 |
+--------+------------+--------------------+
4 rows in set (0.00 sec)
（6）replace(x,y,z)
將字符串z替代字符串x中的字符串y
mysql> select replace(store_name,'ng','xx') from location;
+-------------------------------+
| replace(store_name,'ng','xx') |
+-------------------------------+
| Beijixx |
| Shaxxhai |
| Guaxxzhou |
| Shenzhen |
+-------------------------------+
4 rows in set (0.00 sec)
（7）upper(x)
將字符串x的所有字母變成大寫字符
mysql> select upper(store_name) from location;
+-------------------+
| upper(store_name) |
+-------------------+
| BEIJING |
| SHANGHAI |
| GUANGZHOU |
| SHENZHEN |
+-------------------+
4 rows in set (0.00 sec)
（8）lower(x)
將字符串x的所有字母變成小寫字符
mysql> select lower(store_name) from location;
+-------------------+
| lower(store_name) |
+-------------------+
| beijing |
| shanghai |
| guangzhou |
| shenzhen |
+-------------------+
4 rows in set (0.00 sec)
（9）left(x,y)
返回字符串x的前y個字符
mysql> select left('Beijing',3);
+-------------------+
| left('Beijing',3) |
+-------------------+
| Bei |
+-------------------+
1 row in set (0.00 sec)
（10）right(x,y)
返回字符串x的后y個字符
mysql> select right('Beijing',3);
+--------------------+
| right('Beijing',3) |
+--------------------+
| ing |
+--------------------+
1 row in set (0.00 sec)
（11）reprat(x,y)
將字符串x重復y次
mysql> select repeat('Beijing ',3);
+--------------------------+
| repeat('Beijing ',3) |
+--------------------------+
| Beijing Beijing Beijing |
+--------------------------+
1 row in set (0.00 sec)
（12）space(x)
返回x個空格
mysql> select space(10);
+------------+
| space(10) |
+------------+
| |
+------------+
1 row in set (0.00 sec)
mysql> select space(15);
+-----------------+
| space(15) |
+-----------------+
| |
+-----------------+
1 row in set (0.00 sec)
（13）strcmp(x,y)
比較x和y，返回的值可以為-1,0,1
x=y，返回0
mysql> select strcmp(1,1);
+-------------+
| strcmp(1,1) |
+-------------+
| 0 |
+-------------+
1 row in set (0.00 sec)
x<y，返回-1
mysql> select strcmp(1,2);
+-------------+
| strcmp(1,2) |
+-------------+
| -1 |
+-------------+
1 row in set (0.00 sec)
x>y，返回1
mysql> select strcmp(2,1);
+-------------+
| strcmp(2,1) |
+-------------+
| 1 |
+-------------+
1 row in set (0.00 sec)
（14）reverse(x)
將字符串x反轉
mysql> select reverse(sales) from store_info;
+----------------+
| reverse(sales) |
+----------------+
| 0051 |
| 052 |
| 003 |
| 007 |
+----------------+
4 rows in set (0.00 sec)
四、SQL查詢語句
1. group by
對group by后面的欄位的查詢結果進行匯總分組，通常是結合聚合函數一起使用的。
group by有一個原則，就是select后面的所有列中，沒有使用聚合函數的列，必須出現在group by 后面。
語法：select "欄位1",sum("欄位2") from "表名" group by "欄位1";
mysql> select store_name,sum(sales) from store_info group by store_name order by sales desc;
+------------+------------+
| store_name | sum(sales) |
+------------+------------+
| Guangzhou | 1800 |
| Beijing | 700 |
| Shenzhen | 250 |
+------------+------------+
3 rows in set (0.00 sec)
"Guangzhou"有兩條屬性信息，通過group by分組后，同名項將被合並，可通過以下方式確定是否有重名項以及重名次數。
mysql> select store_name,count(store_name),sum(sales) from store_info group by store_name order by sales desc;
+------------+-------------------+------------+
| store_name | count(store_name) | sum(sales) |
+------------+-------------------+------------+
| Guangzhou | 2 | 1800 |
| Beijing | 1 | 700 |
| Shenzhen | 1 | 250 |
+------------+-------------------+------------+
3 rows in set (0.00 sec)
也可通過前后sales是否變化，判斷是否有重名項被合並。
mysql> select store_name,sales,sum(sales) from store_info group by store_name order by sales desc;
+------------+-------+------------+
| store_name | sales | sum(sales) |
+------------+-------+------------+
| Guangzhou | 1500 | 1800 |
| Beijing | 700 | 700 |
| Shenzhen | 250 | 250 |
+------------+-------+------------+
3 rows in set (0.00 sec)
2. having
用來過濾由group by語句返回的記錄集，通常與group by語句聯合使用。
having語句的存在彌補了where關鍵字不能與聚合函數聯合使用的不足。如果被select的只有函數欄，那就不需要group by子句。
語法：select "欄位1",sum("欄位2") from "表名" group by “欄位1” having (函數條件);
mysql> select store_name,sum(sales) from store_info group by store_name having sum(sales)>1500;
+------------+------------+
| store_name | sum(sales) |
+------------+------------+
| Guangzhou | 1800 |
+------------+------------+
1 row in set (0.00 sec)
3. [as] 別名
欄位別名/表格別名
語法：select "表格別名"."欄位1" [as] "欄位別名" from "表格名" [as] "表格別名";
mysql> select A.store_name as STORE,sum(A.sales) as 'TOTAL_SALES' from store_info as A group by STORE;
+-----------+-------------+
| STORE | TOTAL_SALES |
+-----------+-------------+
| Beijing | 700 |
| Guangzhou | 1800 |
| Shenzhen | 250 |
+-----------+-------------+
3 rows in set (0.00 sec)
4. 子查詢
連接表格，在where子句或having子句中插入另一個SQL語句
語法：slect "欄位1" from "表格1" where "欄位2" [比較運算符] (select "欄位1" from "表格2" where "條件");
其中：
slect "欄位1" from "表格1" where "欄位2" [比較運算符] 為外查詢，
(select "欄位1" from "表格2" where "條件")為內查詢。
[比較運算符]可以是符號的運算符，例如=、>、<、>=、<=；也可以是文字的匹配符，例如like、in、between等。
mysql> select sum(sales) from store_info where store_name in (select store_name from location where region='North');
+------------+
| sum(sales) |
+------------+
| 700 |
+------------+
1 row in set (0.00 sec)
mysql> select sum(A.sales) from store_info A where A.store_name in
-> (select store_name from location B where B.store_name=A.store_name);
+--------------+
| sum(A.sales) |
+--------------+
| 2750 |
+--------------+
1 row in set (0.00 sec)
注：匹配兩個表的列名可以不相同，但列中需有相同內容，否則將返回NULL值。
mysql> alter table location change store_name name char(20);
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> select sum(sales) from store_info where store_name in (select name from location where region='North');
+------------+
| sum(sales) |
+------------+
| 700 |
+------------+
1 row in set (0.00 sec)
mysql> select sum(sales) from store_info where sales in (select name from locattion where region='North');
+------------+
| sum(sales) |
+------------+
| NULL |
+------------+
1 row in set, 4 warnings (0.00 sec)
5. exists
用來測試內查詢有沒有產生任何結果，類似布爾值是否為真。
如果有的話，系統就會執行外查詢中的SQL語句。若沒有的話，那整個SQL就不會產生任何結果。
語法：select "欄位1" from "表格1" where exists (select * from "表格2" where "條件");
mysql> select sum(sales) from store_info where exists
-> (select * from location where region='North');
+------------+
| sum(sales) |
+------------+
| 2750 |
+------------+
1 row in set (0.00 sec)
6. join--連接查詢
inner join（內連接）：只返回兩個表中聯結字段相等的行
mysql> select * from location A inner join store_info B on A.store_name=B.store_name;
+--------+------------+------------+-------+------------+
| region | store_name | store_name | sales | date |
+--------+------------+------------+-------+------------+
| South | Guangzhou | Guangzhou | 1500 | 2020-12-05 |
| South | Shenzhen | Shenzhen | 250 | 2020-12-07 |
| South | Guangzhou | Guangzhou | 300 | 2020-12-08 |
| North | Beijing | Beijing | 700 | 2020-12-08 |
+--------+------------+------------+-------+------------+
4 rows in set (0.00 sec)
left join（左連接）：返回包括左表中的所有記錄和右表中連接字段相等的記錄
mysql> select * from location A left join store_info B on A.store_name=B.store__name;
+--------+------------+------------+-------+------------+
| region | store_name | store_name | sales | date |
+--------+------------+------------+-------+------------+
| South | Guangzhou | Guangzhou | 1500 | 2020-12-05 |
| South | Shenzhen | Shenzhen | 250 | 2020-12-07 |
| South | Guangzhou | Guangzhou | 300 | 2020-12-08 |
| North | Beijing | Beijing | 700 | 2020-12-08 |
| East | Shanghai | NULL | NULL | NULL |
+--------+------------+------------+-------+------------+
5 rows in set (0.00 sec)
right join（右連接）：返回包括右表中所有記錄和左表中聯結字段相等的記錄
mysql> select * from location A right join store_info B on A.store_name=B.store_name;
+--------+------------+------------+-------+------------+
| region | store_name | store_name | sales | date |
+--------+------------+------------+-------+------------+
| North | Beijing | Beijing | 700 | 2020-12-08 |
| South | Guangzhou | Guangzhou | 1500 | 2020-12-05 |
| South | Guangzhou | Guangzhou | 300 | 2020-12-08 |
| South | Shenzhen | Shenzhen | 250 | 2020-12-07 |
+--------+------------+------------+-------+------------+
4 rows in set (0.00 sec)
也可以通過from多表后where添加同名條件達到與連接查詢相同的效果
mysql> select * from location A,store_info B where A.store_name=B.store_name;
+--------+------------+------------+-------+------------+
| region | store_name | store_name | sales | date |
+--------+------------+------------+-------+------------+
| South | Guangzhou | Guangzhou | 1500 | 2020-12-05 |
| South | Shenzhen | Shenzhen | 250 | 2020-12-07 |
| South | Guangzhou | Guangzhou | 300 | 2020-12-08 |
| North | Beijing | Beijing | 700 | 2020-12-08 |
+--------+------------+------------+-------+------------+
4 rows in set (0.00 sec)
也可對其進一步分組操作，實現去重
mysql> select A.region,sum(B.sales) from location A,store_info B
-> where A.store_name=B.store_name group by A.region;
+--------+--------------+
| region | sum(B.sales) |
+--------+--------------+
| North | 700 |
| South | 2050 |
+--------+--------------+
2 rows in set (0.00 sec)
mysql> select A.store_name,sum(B.sales) from location A,store_info B
-> where A.store_name=B.store_name group by A.store_name;
+------------+--------------+
| store_name | sum(B.sales) |
+------------+--------------+
| Beijing | 700 |
| Guangzhou | 1800 |
| Shenzhen | 250 |
+------------+--------------+
3 rows in set (0.00 sec)
五、create view--視圖
1. 視圖的定義
視圖，可以被當作是虛擬表或存儲查詢。
2. 視圖和表格的區別
視圖和表格的不同是，表格中有實際存儲資料，而視圖是建立在表格之上的一個架構，它本身並不實際儲存資料。
臨時表在用戶退出或同數據庫的連接斷開后就自動消失了，而視圖不會消失。
3. 視圖的特點
視圖不含有數據，只存儲它的定義，它的用途一般可以簡化復雜的查詢。比如你要對凈額表進行連接查詢，而且還要進行統計排序等操作，寫SQL語句會很麻煩的，用視圖將幾個表聯結起來，然后對這個視圖進行查詢操作，就和對一個表查詢一樣，很方便。
4. 視圖的語法
create view "視圖表名" as "select 語句";
mysql> create view V_REGION_SALES as
-> select A.region REGION,sum(B.sales) SALES from location A
-> inner join store_info B on A.store_name=B.store_name
-> group by REGION;
Query OK, 0 rows affected (0.01 sec)
5. 查看視圖
視圖保存於當前庫的表列表中，查詢方式同表。
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| V_REGION_SALES |
| city |
| location |
| rank |
| store_info |
| test |
+----------------+
6 rows in set (0.00 sec)
也可使用selct語句對視圖進行查看
mysql> select * from V_REGION_SALES;
+--------+-------+
| REGION | SALES |
+--------+-------+
| North | 700 |
| South | 2050 |
+--------+-------+
2 rows in set (0.00 sec)
6. 刪除視圖
可使用drop view對視圖進行刪除操作。
mysql> drop view V_REGION_SALES;
Query OK, 0 rows affected (0.00 sec)
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| city |
| location |
| rank |
| store_info |
| test |
+----------------+
5 rows in set (0.00 sec)
六、union--聯集
聯集，將兩個SQL語句的結果合並起來，兩個SQL語句所產生的欄位需要是同樣的資料種類。
union：生成結果的資料值將沒有重復，且按照字段的順序進行排序。
語法：[select 語句1] union [select 語句2];
mysql> select store_name from location union select store_name from store_info;
+------------+
| store_name |
+------------+
| Beijing |
| Shanghai |
| Guangzhou |
| Shenzhen |
+------------+
4 rows in set (0.00 sec)
union all：將生成結果的資料值都列出來，無論有誤重復
語法：[select 語句1] all union [select 語句2];
mysql> select store_name from location union all select store_name from store_iinfo;
+------------+
| store_name |
+------------+
| Beijing |
| Shanghai |
| Guangzhou |
| Shenzhen |
| Guangzhou |
| Shenzhen |
| Guangzhou |
| Beijing |
+------------+
8 rows in set (0.00 sec)
七、有/無交集值
取兩個SQL語句結果的交集
1. 出現重復的行
- 可以使用on語句匹配指定列中的相同行
mysql> select A.store_name from location A inner join store_info B on A.store_name=B.store_name;
+------------+
| store_name |
+------------+
| Guangzhou |
| Shenzhen |
| Guangzhou |
| Beijing |
+------------+
4 rows in set (0.00 sec)
- 當兩張表的列名相同時，也可適應using語句進行匹配
mysql> select A.store_name from location A inner join store_info B using(store_name);
+------------+
| store_name |
+------------+
| Guangzhou |
| Shenzhen |
| Guangzhou |
| Beijing |
+------------+
4 rows in set (0.00 sec)
- 也可使用union all將兩張表的指定列合並顯示，然后再通過group by分組去重
mysql> select A.store_name from
-> (select store_name from location union all select store_name from store_info) A
-> group by A.store_name;
+------------+
| store_name |
+------------+
| Beijing |
| Guangzhou |
| Shanghai |
| Shenzhen |
+------------+
4 rows in set (0.00 sec)
2. 兩張表都出現的重復的行
兩張表其中的一個表沒有指定的行，而另一個表這個行有重復時，導致以上方法仍會返回該行內容，因此我們需要使用以下幾種方式將其修正為兩張表都有指定行的時候才會返回該行。
- 也可使用union all將兩張表的指定列合並顯示，然后再通過group by分組去重，最后使用having語句匹配該列出現次數大於1的行
mysql> select A.store_name from
-> (select store_name from location union all select store_name from store_info) A
-> group by A.store_name having count(*)>1;
+------------+
| store_name |
+------------+
| Beijing |
| Guangzhou |
| Shenzhen |
+------------+
3 rows in set (0.00 sec)
- 使用內連接的方式匹配兩張表中指定列都出現的行，然后通過group by分組去重
mysql> select A.store_name from
-> (select B.store_name from location B inner join store_info C on B.store_name=C.store_name) A
-> group by A.store_name;
+------------+
| store_name |
+------------+
| Beijing |
| Guangzhou |
| Shenzhen |
+------------+
3 rows in set (0.00 sec)
- 使用distinct語句進行去重后再連接兩張表，並使用using語句匹配指定列（兩張表指定列名需相同）
mysql> select distinct A.store_name from location A inner join store_info B using(store_name);
+------------+
| store_name |
+------------+
| Guangzhou |
| Shenzhen |
| Beijing |
+------------+
3 rows in set (0.00 sec)
- 先用distinct將兩張表都去重后再去匹配指定列的相同行
mysql> select distinct store_name from location where (store_name) in
-> (select distinct store_name from store_info);
+------------+
| store_name |
+------------+
| Guangzhou |
| Shenzhen |
| Beijing |
+------------+
3 rows in set (0.00 sec)
- 使用distinct去重后左連接后using指定列去匹配
mysql> select distinct A.store_name from location A
-> left join store_info B using(store_name)
-> where B.store_name is not null;
+------------+
| store_name |
+------------+
| Beijing |
| Guangzhou |
| Shenzhen |
+------------+
3 rows in set (0.00 sec)
3. 無交集值
顯示第一個SQL語句的結果，且與第二個SQL語句沒有交集的結果，且沒有重復
mysql> select distinct store_name from location where (store_name) not in
-> (select store_name from store_info);
+------------+
| store_name |
+------------+
| Shanghai |
+------------+
1 row in set (0.00 sec)
mysql> select distinct A.store_name from location A left join store_info B using(store_name) where B.store_name is null;
+------------+
| store_name |
+------------+
| Shanghai |
+------------+
1 row in set (0.00 sec)
mysql> select A.store_name from
-> (select distinct store_name from location union all select distinct store_name from store_info) A
-> group by A.store_name having count(*)=1;
+------------+
| store_name |
+------------+
| Shanghai |
+------------+
1 row in set (0.00 sec)
八、case
1. case概述
case是SQL用來做if-then-else之類邏輯的關鍵字
2. case語法
select case ("欄位名")
when "條件1" then "結果1"
when "條件2" then "結果2"
...
[else "結果N"]
end
from "表名";
條件：可以是一個數值或是一個公式，else子句並不是必須的
3. case使用實例
mysql> select store_name,case store_name
-> when 'Beijing' then sales *2
-> when 'Shenzhen' then 1000
-> else sales
-> end
-> 'new sales',date
-> from store_info;
+------------+-----------+------------+
| store_name | new sales | date |
+------------+-----------+------------+
| Guangzhou | 1500 | 2020-12-05 |
| Shenzhen | 1000 | 2020-12-07 |
| Guangzhou | 300 | 2020-12-08 |
| Beijing | 1400 | 2020-12-08 |
+------------+-----------+------------+
4 rows in set (0.00 sec)
then 數字，將直接返回該數字，即重新為匹配行賦值
'new sales'是用於case字段的字段名
九、常用算法
1. 排名
表格自我連結（self join），然后將結果依序列出，算出每一行之前（包含那一行本身）有多少行數
mysql> select A1.name,A1.sales,count(A2.sales) rank from total_sales A1,total_sales A2
-> where A1.sales < A2.sales or
-> (A1.sales = A2.sales and A1.name = A2.name)
-> group by A1.name,A1.sales order by A1.sales desc;
+----------+-------+------+
| name | sales | rank |
+----------+-------+------+
| sunqi | 50 | 1 |
| zhaoliu | 40 | 2 |
| wujiu | 30 | 3 |
| wangwu | 20 | 4 |
| zhouba | 20 | 4 |
| lisi | 15 | 6 |
| zhangsan | 10 | 7 |
+----------+-------+------+
7 rows in set (0.00 sec)
統計sales字段的值是比自己本身的值小的以及sales字段和name字段都相同的數量，比如zhangsan為6+1=7。
由於wangwu和zhouba的sales列都為20，並列第四，若需將他倆分出第四和第五，可用以下方法（由於sales相同，只能根據name進行區分排序）
mysql> select A1.name,A1.sales,count(A2.sales) rank from total_sales A1,total_sales A2
-> where A1.sales < A2.sales or
-> (A1.sales = A2.sales and A1.name >= A2.name)
-> group by A1.name,A1.sales order by A1.sales desc;
+----------+-------+------+
| name | sales | rank |
+----------+-------+------+
| sunqi | 50 | 1 |
| zhaoliu | 40 | 2 |
| wujiu | 30 | 3 |
| wangwu | 20 | 4 |
| zhouba | 20 | 5 |
| lisi | 15 | 6 |
| zhangsan | 10 | 7 |
+----------+-------+------+
7 rows in set (0.00 sec)
2. 中位數
中位排名取值1：通過ceil取(行數/2)后的最小整數
mysql> select name,sales middle from
-> (select A1.name,A1.sales,count(A2.sales) rank from total_sales A1,total_sales A2
-> where A1.sales < A2.sales or (A1.sales = A2.sales and A1.name >= A2.name)
-> group by A1.name,A1.sales order by A1.sales desc) A3
-> where A3.rank = (select ceil(count(rank)/2) from total_sales);
+--------+--------+
| name | middle |
+--------+--------+
| wangwu | 20 |
+--------+--------+
1 row in set (0.00 sec)
中位排名取值2：將(行數+1)/2取商
mysql> select name,sales middle from
-> (select A1.name,A1.sales,count(A2.sales) rank from total_sales A1,total_sales A2
-> where A1.sales < A2.sales or (A1.sales = A2.sales and A1.name >= A2.name)
-> group by A1.name,A1.sales order by A1.sales desc) A3
-> where A3.rank = (select (count(*)+1) div 2 from total_sales);
+--------+--------+
| name | middle |
+--------+--------+
| wangwu | 20 |
+--------+--------+
1 row in set (0.00 sec)
div是在MySQL中算出商的方式
每個派生表必須有自己的別名，所以別名A3必須要有
也可使用view視圖進行操作
mysql> create view V1 as
-> select A1.name,A1.sales,count(A2.sales) rank from total_sales A1,total_sales A2
-> where A1.sales < A2.sales or (A1.sales = A2.sales and A1.name >= A2.name)
-> group by A1.name,A1.sales order by A1.sales desc;
Query OK, 0 rows affected (0.00 sec)
mysql> select name,sales middle from V1
-> where rank = (select ceil(count(rank)/2) from total_sales);
+--------+--------+
| name | middle |
+--------+--------+
| wangwu | 20 |
+--------+--------+
1 row in set (0.00 sec)
3. 累計總計
表格自我連結（self join），然后將結果依序列出，算出每一行之前（包含哪一行本身）的總合
mysql> select A1.name,A1.sales,sum(A2.sales) sum_total,count(A2.sales) rank from total_sales A1,total_sales A2
-> where A1.sales < A2.sales or (A1.sales = A2.sales and A1.name >= A2.namee)
-> group by A1.name,A1.sales order by A1.sales desc;
+----------+-------+-----------+------+
| name | sales | sum_total | rank |
+----------+-------+-----------+------+
| sunqi | 50 | 50 | 1 |
| zhaoliu | 40 | 90 | 2 |
| wujiu | 30 | 120 | 3 |
| wangwu | 20 | 140 | 4 |
| zhouba | 20 | 160 | 5 |
| lisi | 15 | 175 | 6 |
| zhangsan | 10 | 185 | 7 |
+----------+-------+-----------+------+
7 rows in set (0.00 sec)
4. 總合百分比
mysql> select A1.name,A1.sales,A1.sales/(select sum(sales) from total_sales) peer_total,count(A2.sales) rank from total_sales A1,total_sales A2
-> where A1.sales < A2.sales or (A1.sales = A2.sales and A1.name >= A2.name)
-> group by A1.name,A1.sales order by A1.sales desc;
+----------+-------+-----------+------+
| name | sales | per_total | rank |
+----------+-------+-----------+------+
| sunqi | 50 | 0.2703 | 1 |
| zhaoliu | 40 | 0.2162 | 2 |
| wujiu | 30 | 0.1622 | 3 |
| zhouba | 20 | 0.1081 | 5 |
| wangwu | 20 | 0.1081 | 4 |
| lisi | 15 | 0.0811 | 6 |
| zhangsan | 10 | 0.0541 | 7 |
+----------+-------+-----------+------+
7 rows in set (0.00 sec)
select sum(sales) from total_sales這一段子查詢用來算出總合；
總合算出來后，我們就能夠將每一行除以總合來求出每一行的總和百分比。
若需要顯示小數后兩位的百分數，可使用"round(A1.sales/(select sum(sales) from total_sales)*100,2) || '%'"的操作。
mysql> select A1.name,A1.sales,round(A1.sales/(select sum(sales) from total_sales)*100,2) || '%' per_total,count(A2.sales) rank from total_sales A1,total_sales A2
-> where A1.sales < A2.sales or (A1.sales = A2.sales and A1.name >= A2.name)
-> group by A1.name,A1.sales order by A1.sales desc;
+----------+-------+-----------+------+
| name | sales | per_total | rank |
+----------+-------+-----------+------+
| sunqi | 50 | 27.03% | 1 |
| zhaoliu | 40 | 21.62% | 2 |
| wujiu | 30 | 16.22% | 3 |
| wangwu | 20 | 10.81% | 4 |
| zhouba | 20 | 10.81% | 5 |
| lisi | 15 | 8.11% | 6 |
| zhangsan | 10 | 5.41% | 7 |
+----------+-------+-----------+------+
7 rows in set (0.00 sec)
5. 累計總合百分比
mysql> select A1.name,A1.sales,sum(A2.sales)/(select sum(sales) from total_sales) per_total,count(A2.sales) rank from total_sales A1,total_sales A2
-> where A1.sales < A2.sales or (A1.sales = A2.sales and A1.name >= A2.name)
-> group by A1.name,A1.sales order by A1.sales desc;
+----------+-------+-----------+------+
| name | sales | per_total | rank |
+----------+-------+-----------+------+
| sunqi | 50 | 0.2703 | 1 |
| zhaoliu | 40 | 0.4865 | 2 |
| wujiu | 30 | 0.6486 | 3 |
| wangwu | 20 | 0.7568 | 4 |
| zhouba | 20 | 0.8649 | 5 |
| lisi | 15 | 0.9459 | 6 |
| zhangsan | 10 | 1.0000 | 7 |
+----------+-------+-----------+------+
7 rows in set (0.00 sec)
顯示小數后兩位的百分數
mysql> select A1.name,A1.sales,round(sum(A2.sales)/(select sum(sales) from total_salal_sales)*100,2) || '%' per_total,count(A2.sales) rank from total_sales A1,totaal_sales A2
-> where A1.sales < A2.sales or (A1.sales = A2.sales and A1.name >= A2.name)
-> group by A1.name,A1.sales order by A1.sales desc;
+----------+-------+-----------+------+
| name | sales | per_total | rank |
+----------+-------+-----------+------+
| sunqi | 50 | 27.03% | 1 |
| zhaoliu | 40 | 48.65% | 2 |
| wujiu | 30 | 64.86% | 3 |
| wangwu | 20 | 75.68% | 4 |
| zhouba | 20 | 86.49% | 5 |
| lisi | 15 | 94.59% | 6 |
| zhangsan | 10 | 100.00% | 7 |
+----------+-------+-----------+------+
7 rows in set (0.00 sec)
十、空值(NULL)和無值('')的區別
- 無值的長度為0，不占用空間；而NULL值的長度是NULL，占用空間。
mysql> select length(NULL),length(''),length('1');
+--------------+------------+-------------+
| length(NULL) | length('') | length('1') |
+--------------+------------+-------------+
| NULL | 0 | 1 |
+--------------+------------+-------------+
1 row in set (0.00 sec)
- is null或者is not mull，是用來判斷字段是不是為NULL，不能查出是不是無值。
mysql> select * from city where city_name is null;
+-----------+
| city_name |
+-----------+
| NULL |
| NULL |
+-----------+
2 rows in set (0.00 sec)
mysql> select * from city where city_name is not null;
+-----------+
| city_name |
+-----------+
| beijing |
| nanjing |
| shanghai |
| |
+-----------+
4 rows in set (0.00 sec)
- 無值的判斷使用=''、<>''或!=''來處理，<>和!=代表不等於。
mysql> select * from city where city_name = '';
+-----------+
| city_name |
+-----------+
| |
+-----------+
1 row in set (0.00 sec)
mysql> select * from city where city_name <> '';
+-----------+
| city_name |
+-----------+
| beijing |
| nanjing |
| shanghai |
+-----------+
3 rows in set (0.00 sec)
mysql> select * from city where city_name != '';
+-----------+
| city_name |
+-----------+
| beijing |
| nanjing |
| shanghai |
+-----------+
3 rows in set (0.00 sec)
注：<>''和!=''為不是無值的行，但NULL本質上也沒有實際值，因此也會被忽略。
- 在通過count()指定字段統計有多少行數時，如果遇到NULL值會自動忽略掉，遇到無值會加入到記錄中進行計算。
mysql> select count(*) from city;
+----------+
| count(*) |
+----------+
| 6 |
+----------+
1 row in set (0.00 sec)
mysql> select count(city_name) from city;
+------------------+
| count(city_name) |
+------------------+
| 4 |
+------------------+
1 row in set (0.00 sec)
十一、正則表達式
| 匹配模式 | 描述 | 實例 |
|---|---|---|
| ^ | 匹配文本的開始字符 | '^a'匹配以a開頭的字符串 |
| $ | 匹配文本的結束字符 | 'a$'匹配以a結尾的字符串 |
| . | 匹配任何單個字符 | 'a.c'匹配任何a和c之間有一個字符的字符串 |
| * | 匹配零個或多個在它前面的字符 | 'ye*p'匹配p前面有任意個e |
| + | 匹配前面的字符1次或多次 | 'hi+'匹配以hi開頭，后面至少一個i的字符串 |
| 字符串 | 匹配包含指定的字符串 | 'test'匹配含有test的字符串 |
| a|b | 匹配a或b | 'test|wrok'匹配test或者work |
| [...] | 匹配字符集合中的任意一個字符 | '[abc]'匹配a或者b或者c |
| [^...] | 匹配不在括號中的字符 | '[abc]'匹配不包含a或者b或者c的字符串 |
| {n} | 匹配前面的字符串n次 | 'a{2}'匹配含有2個a的字符串 |
| {n,m} | 匹配前面的字符串至少n次，至多m次 | 'a{1,2}'匹配a至少1次，至多2次 |
語法：select "字段" from "表名" where "字段" regexp {模式};
mysql> select * from store_info where store_name regexp 'ng';
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Guangzhou | 1500 | 2020-12-05 |
| Guangzhou | 300 | 2020-12-08 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
3 rows in set (0.00 sec)
mysql> select * from store_info where store_name regexp '^[A-C]';
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
1 row in set (0.00 sec)
mysql> select * from store_info where store_name regexp 'ei|en';
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Shenzhen | 250 | 2020-12-07 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
2 rows in set (0.00 sec)
十二、存儲過程
1. 存儲過程的定義
存儲過程是一組為了完成特定功能的SQL語句集合，類似於shell中的函數。
存儲過程在使用過程中是將常用或者復雜的工作預先使用SQL語句寫好並用一個指定的名稱存儲起來，這個過程經編譯和優化后存儲在數據庫服務器中。當需要使用該存儲過程時，只需要調用它即可。存儲過程在執行上比傳統SQL速度更快、執行效率更高。
2. 存儲過程的優點
- 執行一次后，會將生成的二進制代碼駐留緩沖區，提高執行效率。
- SQL語句加上控制語句的集合，靈活性高。
- 在服務器端存儲，客戶端調用時，降低網絡負載。
- 可多次重復被調用，可隨時修改，不影響客戶端調用。
- 可完成所有的數據庫操作，也可控制數據庫的信息訪問權限。
3. 創建存儲過程
mysql> delimiter $$
#將語句的結束符號從分號;臨時改為$$(可以是自定義)
mysql> create procedure test()
#創建存儲過程，過程名為test，不帶參數
-> begin
#過程體以關鍵字begin開始
-> select * from store_info;
#過程體語句
-> end $$
#過程體以關鍵字end結束
Query OK, 0 rows affected (0.01 sec)
mysql> delimiter ;
#將語句的結束符號恢復為分號;
4. 調用存儲過程
mysql> call test;
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Guangzhou | 1500 | 2020-12-05 |
| Shenzhen | 250 | 2020-12-07 |
| Guangzhou | 300 | 2020-12-08 |
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
4 rows in set (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
5. 查看存儲過程
show create procedure [數據庫.]存儲過程名
查看某個存儲過程的具體信息
mysql> show create procedure test;
+-----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| Procedure | sql_mode | Create Procedure | character_set_client | collation_connection | Database Collation |
+-----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| test | PIPES_AS_CONCAT,ANSI_QUOTES,NO_AUTO_VALUE_ON_ZERO,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION | CREATE DEFINER="skip-grants user"@"skip-grants host" PROCEDURE "test"()
begin
select * from store_info;
end | utf8 | utf8_general_ci | utf8_general_ci |
+-----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec)
也可查看procedure狀態並使用like語句進行匹配
mysql> show procedure status like '%test%'\G
*************************** 1. row ***************************
Db: test
Name: test
Type: PROCEDURE
Definer: skip-grants user@skip-grants host
Modified: 2021-09-03 02:40:10
Created: 2021-09-03 02:40:10
Security_type: DEFINER
Comment:
character_set_client: utf8
collation_connection: utf8_general_ci
Database Collation: utf8_general_ci
1 row in set (0.00 sec)
6. 存儲過程的參數
IN 輸入參數：表示調用者向過程傳入值（傳入值可以是字面量或變量）
OUT 輸出參數：表示過程向調用者傳出值（傳出值只能是變量）
INOUT 輸入輸出參數：即表示調用者向過程傳入值，也表示過程向調用者傳出值
mysql> delimiter $$
mysql> create procedure test1(in inname char(20))
-> begin
-> select * from store_info where store_name=inname;
-> end $$
Query OK, 0 rows affected (0.00 sec)
mysql> delimiter ;
mysql> call test1('Beijing');
+------------+-------+------------+
| store_name | sales | date |
+------------+-------+------------+
| Beijing | 700 | 2020-12-08 |
+------------+-------+------------+
1 row in set (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
7. 刪除存儲過程
存儲過程內容到的修改方法使用過刪除原有存儲過程，之后再以相同的名稱創建新的存儲過程。
mysql> drop procedure if exists test;
Query OK, 0 rows affected (0.01 sec)
僅當存在時刪除，不添加if exists時，如果指定過程不存在，則產生一個錯誤
mysql> drop procedure test;
ERROR 1305 (42000): PROCEDURE test.test does not exist
mysql> drop procedure if exists test;
Query OK, 0 rows affected, 1 warning (0.00 sec)
8. 存儲過程的控制語句
制表
mysql> create table t (id int(10));
Query OK, 0 rows affected (0.00 sec)
mysql> insert into t values(10);
Query OK, 1 row affected (0.01 sec)
mysql> select * from t;
+------+
| id |
+------+
| 10 |
+------+
1 row in set (0.00 sec)
（1）條件語句if-then-else...end if
mysql> delimiter $$
mysql> create procedure test(in pro int)
-> begin
-> declare var int;
-> set var=pro*2;
-> if var>=10 then
-> update t set id=id+1;
-> else
-> update t set id=id-1;
-> end if;
-> end $$
Query OK, 0 rows affected (0.00 sec)
mysql> delimiter ;
mysql> call test(6);
Query OK, 1 row affected (0.00 sec)
mysql> select * from t;
+------+
| id |
+------+
| 11 |
+------+
1 row in set (0.00 sec)
mysql> call test(4);
Query OK, 1 row affected (0.00 sec)
mysql> select * from t;
+------+
| id |
+------+
| 10 |
+------+
1 row in set (0.00 sec)
（2）循環語句while...end while
mysql> delimiter $$
mysql> create procedure test2()
-> begin
-> declare var int(10);
-> set var=0;
-> while var<6 do
-> insert into t values(var);
-> set var=var+1;
-> end while;
-> end $$
Query OK, 0 rows affected (0.00 sec)
mysql> delimiter ;
mysql> call test2;
Query OK, 1 row affected (0.01 sec)
mysql> select * from t;
+------+
| id |
+------+
| 10 |
| 0 |
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
+------+
7 rows in set (0.00 sec)