删除mysql数据库中的所有外键

Question

我可以看到有一些问题 [1,2] 已经提出了这个问题，但是解决方案没有包含完整的 SQL 脚本来完成这个任务。 我有一种情况，仅使用 SQL 删除所有外键会非常有帮助。 目前我正在尝试使用存储过程和游标来解决这个问题，如下所示：

-- No automatic commits:
DROP PROCEDURE IF EXISTS removeConstraints;
-- Magic to happen soon:
DELIMITER |
CREATE PROCEDURE removeConstraints()
BEGIN
  SET AUTOCOMMIT=0;
  SET FOREIGN_KEY_CHECKS=0;
  -- https://dev.mysql.com/doc/refman/5.0/en/cursors.html
  -- https://stackoverflow.com/questions/1745165/looping-over-result-sets-in-mysql
  -- https://mariadb.com/kb/en/mariadb/cursor-overview/
  DECLARE done INT DEFAULT FALSE;
  DECLARE s VARCHAR(1024) DEFAULT '';
  DECLARE cur CURSOR FOR SELECT CONCAT('ALTER TABLE ',TABLE_NAME, ' DROP FOREIGN KEY ', CONSTRAINT_NAME, ';')
    FROM INFORMATION_SCHEMA.Key_COLUMN_USAGE
    WHERE REFERENCED_TABLE_NAME IS NOT NULL;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

  OPEN cur;

  read_loop: LOOP
    FETCH cur INTO s;
    IF done THEN
      LEAVE read_loop;
    END IF;
    PREPARE stmt FROM @s;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
  END LOOP;

  CLOSE cur;

  SET FOREIGN_KEY_CHECKS=1;
  COMMIT;
  SET AUTOCOMMIT=1;
END |
DELIMITER ;
-- Do magic:
CALL removeConstraints();
-- Cleanup:
DROP PROCEDURE removeConstraints;

遗憾的是，这会产生以下错误消息：

ERROR 1064 (42000) at line 5: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'DECLARE done INT DEFAULT FALSE;
  DECLARE s VARCHAR(1024) DEFAULT '';
  DECLARE ' at line 8

---

使用来自Ravinder Reddy 的输入，我现在更新了BEGIN 之后的DECLARE 部分，如下所示：

CREATE PROCEDURE removeConstraints()
BEGIN
  DECLARE done INT DEFAULT FALSE;
  DECLARE s VARCHAR(1024) DEFAULT '';
  DECLARE cur CURSOR FOR 
          SELECT DISTINCT CONCAT('ALTER TABLE ',TABLE_NAME,' DROP FOREIGN KEY ',CONSTRAINT_NAME,';')
          FROM INFORMATION_SCHEMA.Key_COLUMN_USAGE
          WHERE TABLE_SCHEMA=DATABASE()
          AND REFERENCED_TABLE_NAME IS NOT NULL;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

  SET AUTOCOMMIT=0;
  SET FOREIGN_KEY_CHECKS=0;

但是当我尝试执行该过程时，我仍然收到错误：

  MariaDB [v4]> CALL removeConstraints();
  ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'NULL' at line 1

我也尝试过使用不同的SELECT 语句，例如：

SELECT CONCAT('ALTER TABLE ',TABLE_NAME,' DROP FOREIGN KEY ',CONSTRAINT_NAME,';')
FROM INFORMATION_SCHEMA.Key_COLUMN_USAGE
WHERE TABLE_SCHEMA=DATABASE()
AND CONSTRAINT_NAME != 'PRIMARY'
AND CONSTRAINT_NAME IS NOT NULL
AND TABLE_NAME IS NOT NULL;

……但它没有帮助。

---

我现在通过更改代码让它工作，以便稍后发生CONCAT。

DROP PROCEDURE IF EXISTS removeConstraints;
-- Magic to happen soon:
DELIMITER |
CREATE PROCEDURE removeConstraints()
BEGIN
  DECLARE done INT DEFAULT FALSE;
  DECLARE tName VARCHAR(64);
  DECLARE cName VARCHAR(64);
  DECLARE cur CURSOR FOR 
          SELECT DISTINCT TABLE_NAME, CONSTRAINT_NAME
          FROM INFORMATION_SCHEMA.Key_COLUMN_USAGE
          WHERE TABLE_SCHEMA=DATABASE()
          AND REFERENCED_TABLE_NAME IS NOT NULL;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

  SET AUTOCOMMIT=0;
  SET FOREIGN_KEY_CHECKS=0;

  OPEN cur;

  read_loop: LOOP
    FETCH cur INTO tName, cName;
    IF done THEN
      LEAVE read_loop;
    END IF;
    SET @sql = CONCAT('ALTER TABLE ',tName,' DROP FOREIGN KEY ',cName,';');
    PREPARE stmt FROM @sql;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
  END LOOP;

  CLOSE cur;

  SET FOREIGN_KEY_CHECKS=1;
  COMMIT;
  SET AUTOCOMMIT=1;
END |
DELIMITER ;
-- Do magic:
CALL removeConstraints();
-- Cleanup:
DROP PROCEDURE removeConstraints;

Answer 1

所有DECLARE 语句必须位于BEGIN - END 块的顶部。

所有其他陈述都应遵循它们。

在您的代码中，您在 DECLARE 语句之前定义了 SET 语句。
将这些语句移至DECLARE 语句的下方。

示例：

  -- https://dev.mysql.com/doc/refman/5.0/en/cursors.html
  -- https://stackoverflow.com/questions/1745165/looping-over-result-sets-in-mysql
  -- https://mariadb.com/kb/en/mariadb/cursor-overview/
  DECLARE done INT DEFAULT FALSE;
  DECLARE s VARCHAR(1024) DEFAULT '';
  DECLARE cur CURSOR FOR 
          SELECT CONCAT('ALTER TABLE ',TABLE_NAME,' DROP FOREIGN KEY ',CONSTRAINT_NAME,';')
            FROM INFORMATION_SCHEMA.Key_COLUMN_USAGE
           WHERE REFERENCED_TABLE_NAME IS NOT NULL;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

  SET AUTOCOMMIT=0;
  SET FOREIGN_KEY_CHECKS=0;

文档参考：

DECLARE Syntax

DECLARE 只允许在 BEGIN ... END 复合语句中 并且必须在它的开头，在任何其他语句之前。

声明必须遵循一定的顺序。游标声明必须 出现在处理程序声明之前。变量和条件 声明必须出现在游标或处理程序声明之前