一、information_schema數據庫表說明:
SCHEMATA表：提供了當前mysql實例中所有數據庫的信息。是show databases的結果取之此表。
TABLES表：提供了關於數據庫中的表的信息（包括視圖）。詳細表述了某個表屬於哪個schema，表類型，表引擎，創建時間等信息。是show tables from schemaname的結果取之此表。
COLUMNS表：提供了表中的列信息。詳細表述了某張表的所有列以及每個列的信息。是show columns from schemaname.tablename的結果取之此表。
STATISTICS表：提供了關於表索引的信息。是show index from schemaname.tablename的結果取之此表。
USER_PRIVILEGES（用戶權限）表：給出了關於全程權限的信息。該信息源自mysql.user授權表。是非標准表。
SCHEMA_PRIVILEGES（方案權限）表：給出了關於方案（數據庫）權限的信息。該信息來自mysql.db授權表。是非標准表。
TABLE_PRIVILEGES（表權限）表：給出了關於表權限的信息。該信息源自mysql.tables_priv授權表。是非標准表。
COLUMN_PRIVILEGES（列權限）表：給出了關於列權限的信息。該信息源自mysql.columns_priv授權表。是非標准表。
CHARACTER_SETS（字符集）表：提供了mysql實例可用字符集的信息。是SHOW CHARACTER SET結果集取之此表。
COLLATIONS表：提供了關於各字符集的對照信息。
COLLATION_CHARACTER_SET_APPLICABILITY表：指明了可用於校對的字符集。這些列等效於SHOW COLLATION的前兩個顯示字段。
TABLE_CONSTRAINTS表：描述了存在約束的表。以及表的約束類型。
KEY_COLUMN_USAGE表：描述了具有約束的鍵列。
ROUTINES表：提供了關於存儲子程序（存儲程序和函數）的信息。此時，ROUTINES表不包含自定義函數（UDF）。名為“mysql.proc name”的列指明了對應於INFORMATION_SCHEMA.ROUTINES表的mysql.proc表列。
VIEWS表：給出了關於數據庫中的視圖的信息。需要有show views權限，否則無法查看視圖信息。
TRIGGERS表：提供了關於觸發程序的信息。必須有super權限才能查看該表
二、存儲過程實現
思路：
1.先判斷表是否存在；
2.判斷列名是否存在該表中；
3.判斷null、default是否存在屬性中；
4.判斷是否需要插入到某個列名之后；
5.拼裝sql語句；
6.執行添加字段的sql語句；
1 drop procedure if exists `AddColumnIfNotExists`; 2 delimiter $$ 3 create procedure AddColumnIfNotExists(in tableName varchar(50),in columnName varchar(50),in discription varchar(256), in position varchar(50)) 4 begin 5 declare tableCount int default 0; #用於判斷表是否存在 6 declare columnCount int default 0; #用於判斷字段是否存在 7 declare stmt varchar(2000); #最終拼接出來的sql語句 8 declare seat int default 0; #用於判斷null/default的位置 9 10 SELECT count(*) into @tableCount FROM information_schema.TABLES WHERE TABLE_SCHEMA = (SELECT DATABASE()) AND TABLE_NAME = tableName; 11 SELECT count(*) into @columnCount FROM information_schema.COLUMNS WHERE TABLE_SCHEMA = (SELECT DATABASE()) AND TABLE_NAME = tableName AND COLUMN_NAME = columnName; 12 13 if @tableCount=1 && @columnCount=0 then 14 set @seat = locate('null', discription); 15 if @seat > 0 then #判斷是否存在null 16 set @stmt = CONCAT(' ALTER TABLE `',tableName,'` ADD COLUMN `',columnName,'` ',discription); 17 else 18 set @seat = locate('default', discription); 19 if @seat > 0 then #判斷是否存在default 20 set @stmt = CONCAT(' ALTER TABLE `',tableName,'` ADD COLUMN `',columnName,'` ',discription, ' NOT NULL'); 21 else 22 set @stmt = CONCAT(' ALTER TABLE `',tableName,'` ADD COLUMN `',columnName,'` ',discription, ' NULL'); 23 end if; 24 end if; 25 26 if position != '' then #判斷是否需要插入某個字段的后面 27 set @stmt = CONCAT(@stmt, ' after ', position, ';'); 28 else 29 set @stmt = CONCAT(@stmt, ';'); 30 end if; 31 32 PREPARE stmt1 FROM @stmt; 33 EXECUTE stmt1; 34 DEALLOCATE PREPARE stmt1; 35 select @stmt; 36 end if; 37 end$$ 38 delimiter ;
三、測試
調用方式：call AddColumnIfNotExists(表名, 字段名,屬性, 插入到那個字段之后);
1.新建一個員工表
#員工表 CREATE TABLE emp( empno MEDIUMINT UNSIGNED NOT NULL DEFAULT 0 comment '編號', ename VARCHAR(20) NOT NULL DEFAULT "" comment '名字', job VARCHAR(9) NOT NULL DEFAULT "" comment '工作', mgr MEDIUMINT UNSIGNED NOT NULL DEFAULT 0 comment '上級編號' )ENGINE=MyISAM DEFAULT CHARSET=utf8 ;
mysql> desc emp; +-------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+-------+ | empno | mediumint(8) unsigned | NO | | 0 | | | ename | varchar(20) | NO | | | | | job | varchar(9) | NO | | | | | mgr | mediumint(8) unsigned | NO | | 0 | | +-------+-----------------------+------+-----+---------+-------+ 4 rows in set (0.01 sec)
2.新插入字段
(1)無null、無default
mysql> call AddColumnIfNotExists('emp', 'hiredatea', 'DATE comment "入職時間"',''); +-------------------------------------------------------------------------+ | @stmt | +-------------------------------------------------------------------------+ | ALTER TABLE `emp` ADD COLUMN `hiredatea` DATE comment "入職時間" NULL; | +-------------------------------------------------------------------------+ 1 row in set (0.09 sec) Query OK, 0 rows affected (0.13 sec) mysql> desc emp; +-----------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------+-----------------------+------+-----+---------+-------+ | empno | mediumint(8) unsigned | NO | | 0 | | | ename | varchar(20) | NO | | | | | job | varchar(9) | NO | | | | | mgr | mediumint(8) unsigned | NO | | 0 | | | hiredatea | date | YES | | NULL | | +-----------+-----------------------+------+-----+---------+-------+ 5 rows in set (0.01 sec)
(2).有not null、無default
mysql> call AddColumnIfNotExists('emp', 'sal', 'DECIMAL(7,2) not null comment " 薪水"', ''); +---------------------------------------------------------------------------+ | @stmt | +---------------------------------------------------------------------------+ | ALTER TABLE `emp` ADD COLUMN `sal` DECIMAL(7,2) not null comment "薪水"; | +---------------------------------------------------------------------------+ 1 row in set (0.06 sec) Query OK, 0 rows affected (0.09 sec) mysql> desc emp; +-----------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------+-----------------------+------+-----+---------+-------+ | empno | mediumint(8) unsigned | NO | | 0 | | | ename | varchar(20) | NO | | | | | job | varchar(9) | NO | | | | | mgr | mediumint(8) unsigned | NO | | 0 | | | hiredatea | date | YES | | NULL | | | sal | decimal(7,2) | NO | | NULL | | +-----------+-----------------------+------+-----+---------+-------+ 6 rows in set (0.01 sec)
(3).無null、有default
mysql> call AddColumnIfNotExists('emp', 'comm', 'DECIMAL(7,2) default 0 comment "紅利"', ''); +--------------------------------------------------------------------------------------+ | @stmt| +--------------------------------------------------------------------------------------+ | ALTER TABLE `emp` ADD COLUMN `comm` DECIMAL(7,2) default 0 comment "紅利" NOT NULL; | +--------------------------------------------------------------------------------------+ 1 row in set (0.06 sec) Query OK, 0 rows affected (0.09 sec) mysql> desc emp; +-----------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------+-----------------------+------+-----+---------+-------+ | empno | mediumint(8) unsigned | NO | | 0 | | | ename | varchar(20) | NO | | | | | job | varchar(9) | NO | | | | | mgr | mediumint(8) unsigned | NO | | 0 | | | hiredatea | date | YES | | NULL | | | sal | decimal(7,2) | NO | | NULL | | | comm | decimal(7,2) | NO | | 0.00 | | +-----------+-----------------------+------+-----+---------+-------+ 7 rows in set (0.01 sec)
(4).有not null、有default、插入都某個字段之后
mysql> call AddColumnIfNotExists('emp', 'deptno', 'varchar(20) not null default "" comment "部門編號"', 'job'); +------------------------------------------------------------------------------------------------------+ | @stmt | +------------------------------------------------------------------------------------------------------+ | ALTER TABLE `emp` ADD COLUMN `deptno` varchar(20) not null default "" comment "部門編號" after job; | +------------------------------------------------------------------------------------------------------+ 1 row in set (0.06 sec) Query OK, 0 rows affected (0.13 sec) mysql> desc emp; +-----------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------+-----------------------+------+-----+---------+-------+ | empno | mediumint(8) unsigned | NO | | 0 | | | ename | varchar(20) | NO | | | | | job | varchar(9) | NO | | | | | deptno | varchar(20) | NO | | | | | mgr | mediumint(8) unsigned | NO | | 0 | | | hiredatea | date | YES | | NULL | | | sal | decimal(7,2) | NO | | NULL | | | comm | decimal(7,2) | NO | | 0.00 | | +-----------+-----------------------+------+-----+---------+-------+ 8 rows in set (0.01 sec)