mysql数据库存储过程游标循环,提前退出 博客分类: mysql 存储过程游标循环失败动态sql增加字段
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2024-03-08 14:02:46
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需求:向trade这个数据库中的每一个表增加多个字段
遇到问题:存储过程,游标,循环,动态sql执行
注意:
mysql存储过程在我所使用的5.5版本中不能使用 show 的命令,利用 information_schema 获得表的相关信息。
游标循环中出现 select into 赋值 为 null 的时候,循环会 提前退出,解决方法有三种
- 不用select into
- select aa into bb,aa改为count(aa),之后的代码由判断null改为判断0
- 当赋值结果为null的时候,会自动修改循环触底的标志,所以手动在循环底部增加 set b = 1;
-- Procedure "useCursor" DDL drop PROCEDURE if exists useCursor; CREATE PROCEDURE `useCursor`() BEGIN /*局部变量的定义 declare*/ declare temp_table_name varchar(100) default ''; declare temp varchar(100); declare b int default 0; /*是否达到记录的末尾控制变量*/ declare cur CURSOR FOR (SELECT table_name from information_schema.`TABLES` where TABLE_SCHEMA = 'trade'); DECLARE CONTINUE HANDLER FOR NOT FOUND SET b = 1; /*开游标*/ OPEN cur; /*游标向下走一步,将查询出来的两个值付给定义的两个变量*/ FETCH cur INTO temp_table_name; WHILE ( b<>1 ) DO #1 SELECT COLUMN_NAME into temp from information_schema.`COLUMNS` where TABLE_SCHEMA = 'trade' and table_name = temp_table_name and COLUMN_NAME = 'bb'; if temp is null then set @sql = concat('alter table ', temp_table_name); set @sql = concat(@sql, ' add bb varchar(50);' ); PREPARE STMT FROM @sql; EXECUTE STMT; DEALLOCATE PREPARE STMT; end if; #2 SELECT COLUMN_NAME into temp from information_schema.`COLUMNS` where TABLE_SCHEMA = 'trade' and table_name = temp_table_name and COLUMN_NAME = 'ww'; if temp is null then set @sql = concat('alter table ', temp_table_name); set @sql = concat(@sql, ' add ww varchar(50);' ); PREPARE STMT FROM @sql; EXECUTE STMT; DEALLOCATE PREPARE STMT; end if; #3 SELECT COLUMN_NAME into temp from information_schema.`COLUMNS` where TABLE_SCHEMA = 'trade' and table_name = temp_table_name and COLUMN_NAME = 'ff'; if temp is null then set @sql = concat('alter table ', temp_table_name); set @sql = concat(@sql, ' add ff varchar(50);' ); PREPARE STMT FROM @sql; EXECUTE STMT; DEALLOCATE PREPARE STMT; end if; #4 SELECT COLUMN_NAME into temp from information_schema.`COLUMNS` where TABLE_SCHEMA = 'trade' and table_name = temp_table_name and COLUMN_NAME = 'pp'; if temp is null then set @sql = concat('alter table ', temp_table_name); set @sql = concat(@sql, ' add pp varchar(50);' ); PREPARE STMT FROM @sql; EXECUTE STMT; DEALLOCATE PREPARE STMT; end if; /*游标向下走一步*/ set b = 0; FETCH cur INTO temp_table_name; END WHILE; CLOSE cur; END; call useCursor; drop PROCEDURE if exists useCursor;