Question

我可以看到有一些问题[1，2]已经提出要求，但解决方案并没有包含完整的SQL脚本来执行此任务。我有一种情况，只使用SQL删除所有外键非常有帮助。目前我正试图用存储过程和游标解决这个问题，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

根据Ravinder Reddy的输入，我现在更新了DECLARE之后的BEGIN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，我仍然会收到错误：

  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

我还尝试使用不同的SELECT语句，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来使其工作，以便CONCAT稍后发生。

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SET语句之前定义了DECLARE个语句将这些语句移到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

  仅在 DECLARE 复合语句中允许
BEGIN ... END   并且必须在任何其他陈述之前开始。

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

删除mysql数据库

1 个答案: