需求：向trade這個數(shù)據庫中的每一個表增加多個字段

遇到問題：存儲過程，游標，循環(huán)，動態(tài)sql執(zhí)行

注意：

mysql 存儲過程在我所使用的5.5版本中不能使用 show 的命令，利用

information_schema 獲得表的相關信息。

游標循環(huán)中出現(xiàn) select into 賦值 為 null 的時候，循環(huán)會 提前退出，解決方法有三種

不用select into

select aa into bb，aa改為count(aa)，之后的代碼由判斷null改為判斷0

當賦值結果為null的時候，會自動修改循環(huán)觸底的標志，所以手動在循環(huán)底部增加 ?set b = 1；

-- Procedure "useCursor" DDL

drop PROCEDURE if exists useCursor;

CREATE PROCEDURE `useCursor`()

BEGIN

/*局部變量的定義 declare*/

declare temp_table_name varchar(100) default '';

declare temp varchar(100);

declare b int default 0; /*是否達到記錄的末尾控制變量*/

declare cur CURSOR FOR (SELECT table_name from information_schema.`TABLES` where TABLE_SCHEMA = 'trade');

DECLARE CONTINUE HANDLER FOR NOT FOUND SET b = 1;

/*開游標*/

OPEN cur;

/*游標向下走一步，將查詢出來的兩個值付給定義的兩個變量*/

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;

/*游標向下走一步*/

set b = 0;

FETCH cur INTO temp_table_name;

END WHILE;

CLOSE cur;

END;

call useCursor;

drop PROCEDURE if exists useCursor;

總結

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