SQL語法基礎之DELETE語句

本文轉載自查看原文 2019-01-16 07:22 1012 MYSQL數據庫

　　　　　　　　　　　　SQL語法基礎之DELETE語句

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　作者：尹正傑

一.查看幫助信息

1>.查看DELETE的幫助信息

mysql> ? DELETE
Name: 'DELETE'
Description:
Syntax:
DELETE is a DML statement that removes rows from a table.

A DELETE statement can start with a WITH clause to define common table
expressions accessible within the DELETE. See
http://dev.mysql.com/doc/refman/8.0/en/with.html.

Single-Table Syntax

DELETE [LOW_PRIORITY] [QUICK] [IGNORE] FROM tbl_name
    [PARTITION (partition_name [, partition_name] ...)]
    [WHERE where_condition]
    [ORDER BY ...]
    [LIMIT row_count]

The DELETE statement deletes rows from tbl_name and returns the number
of deleted rows. To check the number of deleted rows, call the
ROW_COUNT() function described in
http://dev.mysql.com/doc/refman/8.0/en/information-functions.html.

Main Clauses

The conditions in the optional WHERE clause identify which rows to
delete. With no WHERE clause, all rows are deleted.

where_condition is an expression that evaluates to true for each row to
be deleted. It is specified as described in
http://dev.mysql.com/doc/refman/8.0/en/select.html.

If the ORDER BY clause is specified, the rows are deleted in the order
that is specified. The LIMIT clause places a limit on the number of
rows that can be deleted. These clauses apply to single-table deletes,
but not multi-table deletes.

Multiple-Table Syntax

DELETE [LOW_PRIORITY] [QUICK] [IGNORE]
    tbl_name[.*] [, tbl_name[.*]] ...
    FROM table_references
    [WHERE where_condition]

DELETE [LOW_PRIORITY] [QUICK] [IGNORE]
    FROM tbl_name[.*] [, tbl_name[.*]] ...
    USING table_references
    [WHERE where_condition]

Privileges

You need the DELETE privilege on a table to delete rows from it. You
need only the SELECT privilege for any columns that are only read, such
as those named in the WHERE clause.

Performance

When you do not need to know the number of deleted rows, the TRUNCATE
TABLE statement is a faster way to empty a table than a DELETE
statement with no WHERE clause. Unlike DELETE, TRUNCATE TABLE cannot be
used within a transaction or if you have a lock on the table. See [HELP
TRUNCATE TABLE] and [HELP LOCK].

The speed of delete operations may also be affected by factors
discussed in
http://dev.mysql.com/doc/refman/8.0/en/delete-optimization.html.

To ensure that a given DELETE statement does not take too much time,
the MySQL-specific LIMIT row_count clause for DELETE specifies the
maximum number of rows to be deleted. If the number of rows to delete
is larger than the limit, repeat the DELETE statement until the number
of affected rows is less than the LIMIT value.

Subqueries

You cannot delete from a table and select from the same table in a
subquery.

Partitioned Tables

DELETE supports explicit partition selection using the PARTITION
option, which takes a list of the comma-separated names of one or more
partitions or subpartitions (or both) from which to select rows to be
dropped. Partitions not included in the list are ignored. Given a
partitioned table t with a partition named p0, executing the statement
DELETE FROM t PARTITION (p0) has the same effect on the table as
executing ALTER TABLE t TRUNCATE PARTITION (p0); in both cases, all
rows in partition p0 are dropped.

PARTITION can be used along with a WHERE condition, in which case the
condition is tested only on rows in the listed partitions. For example,
DELETE FROM t PARTITION (p0) WHERE c < 5 deletes rows only from
partition p0 for which the condition c < 5 is true; rows in any other
partitions are not checked and thus not affected by the DELETE.

The PARTITION option can also be used in multiple-table DELETE
statements. You can use up to one such option per table named in the
FROM option.

For more information and examples, see
http://dev.mysql.com/doc/refman/8.0/en/partitioning-selection.html.

URL: http://dev.mysql.com/doc/refman/8.0/en/delete.html


mysql>

2>.相關關鍵字說明

　　DELETE語句用於刪除表中已經存儲在的整行數據。查看該語句的幫助信息，如第1步所示。下面是對應的關鍵字說明

    • Tbl_name關鍵詞代表刪除數據的目標表

    • Where子句代表被刪除數據的滿足條件，如果沒有where子句則代
表所有表數據都刪除

    • Order by子句代表刪除數據的順序

    • Limit子句代表被刪除數據的行數限制

二.Delete案例

1>.DELETE 單表刪除舉例

mysql> select * from students;
+-----+-----------+--------+---------+
| sid | sname     | gender | dept_id |
+-----+-----------+--------+---------+
|   1 | 尹正傑    | boy    |       1 |
|   2 | 耿雨星    | boy    |       1 |
|   3 | 鮮惠珊    | girl   |       2 |
|   4 | 白羽      | boy    |       3 |
|   5 | 肖鳳      | girl   |       4 |
+-----+-----------+--------+---------+
5 rows in set (0.00 sec)

mysql> 
mysql> DELETE FROM students;
Query OK, 5 rows affected (0.00 sec)

mysql> 
mysql> select * from students;
Empty set (0.00 sec)

mysql>

刪除整張表數據（mysql> DELETE FROM students;）

mysql> select * from students;
+-----+-----------+--------+---------+
| sid | sname     | gender | dept_id |
+-----+-----------+--------+---------+
|   1 | 尹正傑    | boy    |       1 |
|   2 | 耿雨星    | boy    |       1 |
|   3 | 鮮惠珊    | girl   |       2 |
|   4 | 白羽      | boy    |       3 |
|   5 | 肖鳳      | girl   |       4 |
+-----+-----------+--------+---------+
5 rows in set (0.00 sec)

mysql> 
mysql> 
mysql> DELETE FROM students WHERE sid = 1 ;
Query OK, 1 row affected (0.00 sec)

mysql> 
mysql> select * from students;
+-----+-----------+--------+---------+
| sid | sname     | gender | dept_id |
+-----+-----------+--------+---------+
|   2 | 耿雨星    | boy    |       1 |
|   3 | 鮮惠珊    | girl   |       2 |
|   4 | 白羽      | boy    |       3 |
|   5 | 肖鳳      | girl   |       4 |
+-----+-----------+--------+---------+
4 rows in set (0.00 sec)

mysql>

使用WHERE語句過濾需要刪除掉數據（mysql> DELETE FROM students WHERE sid = 1 ;）

mysql> SELECT * FROM students;
+-----+-----------+--------+---------+
| sid | sname     | gender | dept_id |
+-----+-----------+--------+---------+
|   1 | 尹正傑    | boy    |       1 |
|   2 | 耿雨星    | boy    |       1 |
|   3 | 鮮惠珊    | girl   |       2 |
|   4 | 白羽      | boy    |       3 |
|   5 | 肖鳳      | girl   |       4 |
+-----+-----------+--------+---------+
5 rows in set (0.00 sec)

mysql> 
mysql> 
mysql> DELETE FROM students ORDER BY sid;    
Query OK, 5 rows affected (0.00 sec)

mysql> 
mysql> SELECT * FROM students;
Empty set (0.00 sec)

mysql>

按照sid的值進行升序刪除（mysql> DELETE FROM students ORDER BY sid; ）

mysql> SELECT * FROM students;
+-----+-----------+--------+---------+
| sid | sname     | gender | dept_id |
+-----+-----------+--------+---------+
|   1 | 尹正傑    | boy    |       1 |
|   2 | 耿雨星    | boy    |       1 |
|   3 | 鮮惠珊    | girl   |       2 |
|   4 | 白羽      | boy    |       3 |
|   5 | 肖鳳      | girl   |       4 |
+-----+-----------+--------+---------+
5 rows in set (0.00 sec)

mysql> 
mysql> DELETE FROM students ORDER BY sid LIMIT 1 ;
Query OK, 1 row affected (0.00 sec)

mysql> 
mysql> SELECT * FROM students;
+-----+-----------+--------+---------+
| sid | sname     | gender | dept_id |
+-----+-----------+--------+---------+
|   2 | 耿雨星    | boy    |       1 |
|   3 | 鮮惠珊    | girl   |       2 |
|   4 | 白羽      | boy    |       3 |
|   5 | 肖鳳      | girl   |       4 |
+-----+-----------+--------+---------+
4 rows in set (0.00 sec)

mysql> 
mysql> DELETE FROM students ORDER BY sid DESC LIMIT 1 ;
Query OK, 1 row affected (0.00 sec)

mysql> 
mysql> SELECT * FROM students;
+-----+-----------+--------+---------+
| sid | sname     | gender | dept_id |
+-----+-----------+--------+---------+
|   2 | 耿雨星    | boy    |       1 |
|   3 | 鮮惠珊    | girl   |       2 |
|   4 | 白羽      | boy    |       3 |
+-----+-----------+--------+---------+
3 rows in set (0.00 sec)

mysql>

只刪除先找到的一行（mysql> DELETE FROM students ORDER BY sid LIMIT 1 ;）

mysql> SELECT * FROM students;
+-----+-----------+--------+---------+
| sid | sname     | gender | dept_id |
+-----+-----------+--------+---------+
|   1 | 尹正傑    | boy    |       1 |
|   2 | 耿雨星    | boy    |       1 |
|   3 | 鮮惠珊    | girl   |       2 |
|   4 | 白羽      | boy    |       3 |
|   5 | 肖鳳      | girl   |       4 |
+-----+-----------+--------+---------+
rows in set (0.00 sec)

mysql> 
mysql> DELETE FROM students WHERE dept_id = 1 ORDER BY sid DESC LIMIT 1;
Query OK, 1 row affected (0.00 sec)

mysql> 
mysql> SELECT * FROM students;
+-----+-----------+--------+---------+
| sid | sname     | gender | dept_id |
+-----+-----------+--------+---------+
|   1 | 尹正傑    | boy    |       1 |
|   3 | 鮮惠珊    | girl   |       2 |
|   4 | 白羽      | boy    |       3 |
|   5 | 肖鳳      | girl   |       4 |
+-----+-----------+--------+---------+
rows in set (0.00 sec)

mysql>

Delete語句中的order by子句決定了刪除數據的順序，配合limit子句后在某些情況下也非常有用，比如刪除最老的一條記錄（mysql> DELETE FROM students WHERE dept_id = 1 ORDER BY sid DESC LIMIT 1;）

2>.DELETE 多表刪除語句語法

• 同樣，被刪除的表不能出現在查詢子句的子查詢中

• Low_priority關鍵詞表示刪除語句需要等待其他鏈接的讀此表操作結束后再執行，只作用在MyISAM, MEMORY, and MERGE存儲引擎

• Quick關鍵詞是在使用myisam存儲引擎時，刪除操作不會合並刪除表的索引葉節點，這樣會在一定程度上加快刪除的速度

• ignore關鍵詞代表會忽略刪除過程中的一些錯誤

mysql> SELECT * FROM Dept;
+----+-----------+
| id | demt_name |
+----+-----------+
|  1 | 運維      |
|  2 | 開發      |
|  3 | 測試      |
|  4 | 產品      |
|  5 | 運營      |
|  6 | 法務      |
+----+-----------+
6 rows in set (0.00 sec)

mysql> 
mysql> 
mysql> SELECT * FROM students;
+-----+-----------+--------+---------+
| sid | sname     | gender | dept_id |
+-----+-----------+--------+---------+
|   1 | 尹正傑    | boy    |       1 |
|   2 | 耿雨星    | boy    |       1 |
|   3 | 鮮惠珊    | girl   |       2 |
|   4 | 白羽      | boy    |       3 |
|   5 | 肖鳳      | girl   |       4 |
+-----+-----------+--------+---------+
5 rows in set (0.00 sec)

mysql> 
mysql> DELETE Dept,students FROM Dept INNER JOIN students WHERE Dept.id =students.sid;
Query OK, 10 rows affected (0.00 sec)

mysql> 
mysql> SELECT * FROM Dept;
+----+-----------+
| id | demt_name |
+----+-----------+
|  6 | 法務      |
+----+-----------+
1 row in set (0.00 sec)

mysql> 
mysql> SELECT * FROM students;                                                  Empty set (0.00 sec)

mysql>

從一個或多個表中刪除滿足條件的數據，其中的 table_references代表了多個表的join操作(mysql> DELETE Dept,students FROM Dept INNER JOIN students WHERE Dept.id =students.sid;)

mysql> SELECT * FROM students;
+-----+-----------+--------+---------+
| sid | sname     | gender | dept_id |
+-----+-----------+--------+---------+
|   1 | 尹正傑    | boy    |       1 |
|   2 | 耿雨星    | boy    |       1 |
|   3 | 鮮惠珊    | girl   |       2 |
|   4 | 白羽      | boy    |       3 |
|   5 | 肖鳳      | girl   |       4 |
+-----+-----------+--------+---------+
5 rows in set (0.00 sec)

mysql> 
mysql> SELECT * FROM Dept;
+----+-----------+
| id | demt_name |
+----+-----------+
|  1 | 運維      |
|  2 | 開發      |
|  3 | 測試      |
|  4 | 產品      |
|  5 | 運營      |
|  6 | 法務      |
+----+-----------+
6 rows in set (0.00 sec)

mysql> 
mysql> DELETE FROM students,Dept USING students INNER JOIN Dept WHERE students.sid = Dept.id;
Query OK, 10 rows affected (0.00 sec)

mysql> 
mysql> SELECT * FROM students;                                                  Empty set (0.00 sec)

mysql> 
mysql> SELECT * FROM Dept;                                                      +----+-----------+
| id | demt_name |
+----+-----------+
|  6 | 法務      |
+----+-----------+
1 row in set (0.00 sec)

mysql>

除了上面的那種寫法外，還可以用這種方式寫也能達到相同的效果，如果有多張表繼續使用INNER JOIN關鍵字繼續跟上相應的表即可（mysql> DELETE FROM students,Dept USING students INNER JOIN Dept WHERE students.sid = Dept.id;）

3>.DELETE別名使用方式

mysql> select * from teacher;
+------+-------------+------------+
| t_id | course_name | teacher_id |
+------+-------------+------------+
|    7 | Chinese     |          6 |
|    8 | English     |          7 |
|    9 | Physic      |          8 |
+------+-------------+------------+
3 rows in set (0.00 sec)

mysql> select * from student;
+--------+--------------+
| stu_id | stu_name     |
+--------+--------------+
|      6 | 火影忍者     |
|      7 | 火影忍者     |
|      9 | 沙和尚       |
+--------+--------------+
3 rows in set (0.00 sec)

mysql> 
mysql> DELETE t1,t2 FROM teacher AS t1 INNER JOIN student AS t2 WHERE t1.t_id =t2.stu_id;
Query OK, 4 rows affected (0.01 sec)

mysql> 
mysql> select * from student;                                                   +--------+--------------+
| stu_id | stu_name     |
+--------+--------------+
|      6 | 火影忍者     |
+--------+--------------+
1 row in set (0.00 sec)

mysql> 
mysql> select * from teacher;                                                   +------+-------------+------------+
| t_id | course_name | teacher_id |
+------+-------------+------------+
|    8 | English     |          7 |
+------+-------------+------------+
1 row in set (0.00 sec)

mysql>

mysql> select * from teacher;
+------+-------------+------------+
| t_id | course_name | teacher_id |
+------+-------------+------------+
|    7 | Chinese     |          6 |
|    8 | English     |          7 |
|    9 | Physic      |          8 |
+------+-------------+------------+
3 rows in set (0.00 sec)

mysql> 
mysql> select * from student;
+--------+--------------+
| stu_id | stu_name     |
+--------+--------------+
|      6 | 火影忍者     |
|      7 | 火影忍者     |
|      9 | 沙和尚       |
+--------+--------------+
3 rows in set (0.00 sec)

mysql> 
mysql> DELETE FROM t1,t2 USING teacher AS t1 INNER JOIN student AS t2 WHERE t1.t_id = t2.stu_id;
Query OK, 4 rows affected (0.00 sec)

mysql> 
mysql> select * from student;                                                   +--------+--------------+
| stu_id | stu_name     |
+--------+--------------+
|      6 | 火影忍者     |
+--------+--------------+
1 row in set (0.00 sec)

mysql> 
mysql> select * from teacher;                                                   +------+-------------+------------+
| t_id | course_name | teacher_id |
+------+-------------+------------+
|    8 | English     |          7 |
+------+-------------+------------+
1 row in set (0.00 sec)

mysql>

另一種寫法（mysql> DELETE FROM t1,t2 USING teacher AS t1 INNER JOIN student AS t2 WHERE t1.t_id = t2.stu_id;）

三.DROP、TRUNCATE和DELETE的區別

1>.drop

　　drop是DDL，會隱式提交，所以，不能回滾，不會觸發觸發器。

　　drop語句刪除表結構及所有數據，並將表所占用的空間全部釋放。

　　drop語句將刪除表的結構所依賴的約束，觸發器，索引，依賴於該表的存儲過程/函數將保留,但是變為invalid狀態。

　　相關筆記請參考：https://www.cnblogs.com/yinzhengjie/p/10331914.html。

2>.truncate

　　truncate是DDL，會隱式提交，所以，不能回滾，不會觸發觸發器。

　　truncate會刪除表中所有記錄，並且將重新設置高水線和所有的索引，缺省情況下將空間釋放到minextents個extent，除非使用reuse storage，。不會記錄日志，所以執行速度很快，但不能通過rollback撤消操作（如果一不小心把一個表truncate掉，也是可以恢復的，只是不能通過rollback來恢復）。

　　對於外鍵（foreignkey ）約束引用的表，不能使用 truncate table，而應使用不帶 where 子句的 delete 語句。

　　truncate table不能用於參與了索引視圖的表。

mysql> SHOW TABLES;
+-----------------------+
| Tables_in_yinzhengjie |
+-----------------------+
| course                |
| score_graph           |
| student               |
| teacher               |
| view_teacher          |
+-----------------------+
5 rows in set (0.00 sec)

mysql> 
mysql> SELECT * FROM student;
+----+-----------+------------+
| id | name      | teacher_id |
+----+-----------+------------+
|  1 | 尹正傑    |          1 |
|  2 | 尹正傑    |          1 |
+----+-----------+------------+
2 rows in set (0.00 sec)

mysql> 
mysql> TRUNCATE TABLE student;
Query OK, 0 rows affected (0.01 sec)

mysql> 
mysql> SELECT * FROM student; 
Empty set (0.00 sec)

mysql> 
mysql>

TAUNCATE案例展示（mysql> TRUNCATE TABLE student;）

3>.delete

　　delete是DML，執行delete操作時，每次從表中刪除一行，並且同時將該行的的刪除操作記錄在redo和undo表空間中以便進行回滾（rollback）和重做操作，但要注意表空間要足夠大，需要手動提交（commit）操作才能生效，可以通過rollback撤消操作。

　　delete可根據條件刪除表中滿足條件的數據，如果不指定where子句，那么刪除表中所有記錄。

　　delete語句不影響表所占用的extent，高水線(high watermark)保持原位置不變。

　　相關筆記請參考： https://www.cnblogs.com/yinzhengjie/p/10275086.html。

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