4

您好以下过程必须将所有约束从一个表移动到另一个表，但是我在应该删除约束的地方遇到了一些困难。

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 不识别var_referenced_table_name和var_constraint_name作为变量。

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。

4

1 回答 1

9

使用变量作为列名和表时，最好将DECLARE查询作为“字符串”，然后通过Prepared Statement.

这可以通过两种方式完成，通过CONCAT()构建完整的字符串或使用PREPARE参数：

SET @query = CONCAT('ALTER TABLE ', var_referenced_table_name, ' DROP FOREIGN KEY ', var_constraint_name, ';');
PREPARE stmt FROM @query; 
EXECUTE stmt; 
DEALLOCATE PREPARE stmt;
于 2012-07-27T12:46:25.060 回答