[英]MySQL variables in ALTER TABLE script
您好 以下过程必须将所有约束从一个表移动到另一个表,但是我在删除约束时遇到了一些困难。
问题:如何在以下行中使用变量
ALTER TABLE var_referenced_table_name DROP FOREIGN KEY var_constraint_name;
当我按原样使用时,我收到以下错误
Error Code: 1146. Table 'oaf_businesslink_dev.var_referenced_table_name' doesn't exist
MySQL 不会将var_referenced_table_name
和var_constraint_name
识别为变量。
DELIMITER //
DROP PROCEDURE IF EXISTS AlterConstraints//
CREATE PROCEDURE AlterConstraints()
BEGIN
DECLARE schema_name VARCHAR(60) DEFAULT 'oaf_businesslink_dev';
DECLARE table_name VARCHAR(60) DEFAULT 'wp_systemuser';
DECLARE finished INTEGER DEFAULT 0;
DECLARE total INTEGER DEFAULT 0;
DECLARE var_constraint_name VARCHAR(60) DEFAULT '';
DECLARE var_table_name VARCHAR(60) DEFAULT '';
DECLARE var_column_name VARCHAR(60) DEFAULT '';
DECLARE var_referenced_table_name VARCHAR(60) DEFAULT '';
DECLARE var_referenced_column_name VARCHAR(60) DEFAULT '';
DECLARE cur_constraints CURSOR FOR SELECT constraint_Name, table_name,column_name,referenced_table_name,referenced_column_name
FROM information_schema.key_column_usage
WHERE constraint_schema = schema_name
AND referenced_table_name = table_name
AND table_name IS NOT NULL;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET finished = 1;
OPEN cur_constraints;
get_constraint:
LOOP FETCH cur_constraints
INTO var_constraint_name
,var_table_name
,var_column_name
,var_referenced_table_name
,var_referenced_column_name;
IF finished THEN
LEAVE get_constraint;
END IF;
/* Get Constraint Count */
SET total = total + 1;
/* Remove Constraint */
IF EXISTS(SELECT * FROM information_schema.TABLE_CONSTRAINTS
WHERE CONSTRAINT_NAME = var_constraint_name AND TABLE_NAME = var_referenced_table_name AND TABLE_SCHEMA = schema_name)
THEN
/*
* Error Code: 1146. Table 'oaf_businesslink_dev.var_referenced_table_name' doesn't exist
*/
ALTER TABLE var_referenced_table_name DROP FOREIGN KEY var_constraint_name;
END IF;
/* Change Datatype to BIGINT */
/* Recreate Constraint to new table */
END
LOOP get_constraint;
CLOSE cur_constraints;
SELECT total;
END
//
DELIMITER ;
CALL AlterConstraints();
提前致谢。
随着使用的变量作为列名和表,这将是最好的DECLARE
查询为“串”,然后通过执行该字符串Prepared Statement
。
这可以通过两种方式完成,通过CONCAT()
构建完整字符串或使用带参数的PREPARE
:
SET @query = CONCAT('ALTER TABLE ', var_referenced_table_name, ' DROP FOREIGN KEY ', var_constraint_name, ';');
PREPARE stmt FROM @query;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
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