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我在我的 MySQL 数据库中使用约束。但是现在,当我尝试删除其他条目具有外键关系的条目时,这让我很头疼。我总是收到这个错误:

Cannot delete or update a parent row: a foreign key constraint fails

我可以向删除语句传递任何参数或任何东西,以便它递归地删除与我要删除的行具有外键关系的所有行吗?

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2 回答 2

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更新:现在已将其制成博客文章:https ://stevettt.blogspot.co.uk/2018/02/how-to-automate-deletion-of-rows-in.html


我编写了一个存储过程,它将递归地从所有外键链接表中删除(无需关闭外键检查或打开级联删除)。该实现有一些复杂性,但可以被视为一个“黑匣子”:只需指定模式(数据库)、表的名称和一个 WHERE 子句来限制要删除的记录,剩下的就交给它了。

演示

Rextester 在线演示:http ://rextester.com/MDMRA15991

SQL

-- ------------------------------------------------------------------------------------
-- USAGE
-- ------------------------------------------------------------------------------------
-- CALL delete_recursive(<schema name>, <table name>, <WHERE clause>, <delete flag>);
-- where:
-- <schema name> is the name of the MySQL schema
-- <table name> is the name of the base table to delete records from
-- <WHERE clase> is a SQL WHERE clause to filter which records that are to be deleted
-- <delete flag> is either TRUE or FALSE: If TRUE, the records *will* be deleted.
--               If FALSE, the SQL will be output without actually deleting anything.
-- Example:
-- CALL delete_recursive('mydb', 'mytable', 'WHERE mypk IN (1, 2, 3)', TRUE);
DROP PROCEDURE IF EXISTS delete_recursive;
DELIMITER //
CREATE PROCEDURE delete_recursive(schema_name VARCHAR(64),
                                  tbl_name VARCHAR(64),
                                  where_clause TEXT,
                                  do_delete BIT)
BEGIN
  DECLARE next_schema_name, next_tbl_name VARCHAR(64);
  DECLARE from_clause, next_where_clause, next_col_names, ref_col_names TEXT;
  DECLARE done INT DEFAULT FALSE;
  DECLARE cursor1 CURSOR FOR
    SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAMES, REF_COLUMN_NAMES FROM temp_kcu;
  DECLARE cursor2 CURSOR FOR
    SELECT table_schema, table_name, where_sql FROM temp_deletes ORDER BY id;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

  -- Set maximum recursion depth
  SET @@SESSION.max_sp_recursion_depth = 255;

  -- Increment current recursion depth since the stored procedure has been entered.
  SET @recursion_depth = IFNULL(@recursion_depth + 1, 0);

  -- Create temporary table for storing the deletes if it doesn't already exist
  IF @recursion_depth = 0 THEN
    DROP TEMPORARY TABLE IF EXISTS temp_deletes;
    CREATE TEMPORARY TABLE temp_deletes (
      id INT NOT NULL AUTO_INCREMENT,
      table_schema VARCHAR(64),
      table_name VARCHAR(64),
      where_sql TEXT,
      Notes TEXT,
      PRIMARY KEY(id)
    );
  END IF;

  -- Construct FROM clause (including the WHERE clause) for this table.
  SET from_clause = 
    CONCAT(' FROM ', schema_name, '.', tbl_name, ' WHERE ', where_clause);

  -- Find out whether there are any foreign keys to this table
  SET @query = CONCAT('SELECT COUNT(*) INTO @count', from_clause);
  PREPARE stmt FROM @query;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt;

  IF @count > 0 THEN
    -- There are foriegn keys to this table so all linked rows must be deleted first:
    -- Firstly, fill a temporary table with the foreign key metadata.
    DROP TEMPORARY TABLE IF EXISTS temp_kcu;
    SET @query = CONCAT(
      'CREATE TEMPORARY TABLE temp_kcu AS ',
      'SELECT TABLE_SCHEMA, TABLE_NAME, ',
      'GROUP_CONCAT(CONCAT(COLUMN_NAME) SEPARATOR '', '') AS COLUMN_NAMES, ', 
      'GROUP_CONCAT(CONCAT(REFERENCED_COLUMN_NAME) SEPARATOR '', '')
        AS REF_COLUMN_NAMES ',
      'FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE ',
      'WHERE REFERENCED_TABLE_SCHEMA = ''', schema_name,
      ''' AND REFERENCED_TABLE_NAME = ''', tbl_name, ''' ',
      'GROUP BY CONSTRAINT_NAME');
    PREPARE stmt FROM @query;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;

    -- Loop through all foreign keys to this table using a cursor.
    OPEN cursor1;
    read_loop: LOOP
      FETCH cursor1 INTO next_schema_name, next_tbl_name, next_col_names,
            ref_col_names;
      IF done THEN
        -- No more rows so exit the loop.
        LEAVE read_loop;
      END IF;

      -- Recursively call the stored procedure to delete linked rows
      -- for this foreign key.
      IF INSTR(next_col_names, ',') = 0 THEN
        SET next_where_clause = CONCAT(
          next_col_names, ' IN (SELECT ', ref_col_names, from_clause, ')');
      ELSE
        SET next_where_clause = CONCAT(
          '(', next_col_names, ') IN (SELECT ', ref_col_names, from_clause, ')');
      END IF;
      CALL delete_recursive(
        next_schema_name, next_tbl_name, next_where_clause, do_delete);
    END LOOP;
    CLOSE cursor1;
  END IF;

  -- Build the DELETE statement
  SET @query = CONCAT(
    'DELETE FROM ', schema_name, '.', tbl_name, ' WHERE ', where_clause);

  -- Get the number of primary key columns
  SET @pk_column_count = (SELECT COUNT(*)
                          FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
                          WHERE TABLE_SCHEMA = schema_name
                            AND TABLE_NAME = tbl_name
                            AND CONSTRAINT_NAME = 'PRIMARY');
  IF @pk_column_count = 0 THEN
    -- No primary key so just output the number of rows to be deleted
    SET @query = CONCAT(
      'SET @notes = CONCAT(''No primary key; number of rows to delete = '',
      (SELECT COUNT(*) FROM ', schema_name, '.', tbl_name, ' WHERE ',
      where_clause, '))');
    PREPARE stmt FROM @query;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
  ELSEIF @pk_column_count = 1 THEN
    -- 1 primary key column.
    -- Output the primary keys of the records to be deleted
    SET @pk_column = (SELECT COLUMN_NAME
                      FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
                      WHERE TABLE_SCHEMA = schema_name
                        AND TABLE_NAME = tbl_name
                        AND CONSTRAINT_NAME = 'PRIMARY');
    SET @pk_column_csv = CONCAT('CONCAT('''''''', ', @pk_column, ', '''''''')');
    SET @query = CONCAT(
      'SET @notes = (SELECT CONCAT(''', @pk_column, ' IN ('', GROUP_CONCAT(',
      @pk_column_csv, ' SEPARATOR '', ''), '')'') FROM ',
      schema_name, '.', tbl_name, ' WHERE ', where_clause, ')');
    PREPARE stmt FROM @query;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
  ELSE
    -- Multiple primary key columns.
    -- Output the primary keys of the records to be deleted.
    SET @pk_columns = (SELECT GROUP_CONCAT(COLUMN_NAME SEPARATOR ', ')
                       FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
                       WHERE TABLE_SCHEMA = schema_name
                         AND TABLE_NAME = tbl_name
                         AND CONSTRAINT_NAME = 'PRIMARY');
    SET @pk_columns_csv = (SELECT CONCAT('CONCAT(''('''''', ', GROUP_CONCAT(COLUMN_NAME
                             SEPARATOR ', '''''', '''''', '), ', '''''')'')')
                           FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
                           WHERE TABLE_SCHEMA = schema_name
                             AND TABLE_NAME = tbl_name
                             AND CONSTRAINT_NAME = 'PRIMARY');      
    SET @query = CONCAT(
     'SET @notes = (SELECT CONCAT(''(', @pk_columns,
     ') IN ('', GROUP_CONCAT(', @pk_columns_csv, ' SEPARATOR '', ''), '')'') FROM ',
      schema_name, '.', tbl_name, ' WHERE ', where_clause, ')');
    PREPARE stmt FROM @query;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
  END IF;

  IF @notes IS NULL THEN
    SET @notes = 'No affected rows.';
  END IF;

  -- Save details of the DELETE statement to be executed
  INSERT INTO temp_deletes (table_schema, table_name, where_sql, Notes)
  VALUES (schema_name, tbl_name, where_clause, @notes);

  IF @recursion_depth = 0 THEN
    -- Output the deletes.
    SELECT CONCAT('DELETE FROM ', schema_name, '.', table_name,
                  ' WHERE ', where_sql) `SQL`,
           Notes
    FROM temp_deletes ORDER BY id;

    IF do_delete THEN
      -- Perform the deletes: Loop through all delete queries using a cursor.
      SET done = FALSE;
      OPEN cursor2;
      read_loop: LOOP
        FETCH cursor2 INTO schema_name, tbl_name, where_clause;
        IF done THEN
          -- No more rows so exit the loop.
          LEAVE read_loop;
        END IF;

        SET @query = CONCAT(
          'DELETE FROM ', schema_name, '.', tbl_name, ' WHERE ', where_clause);

        PREPARE stmt FROM @query;
        EXECUTE stmt;
        DEALLOCATE PREPARE stmt;
      END LOOP;
      CLOSE cursor2;
    END IF;

    -- Tidy up
    DROP TEMPORARY TABLE IF EXISTS temp_deletes;
  END IF;

  -- Decrement current recursion depth since the stored procedure is being exited.
  SET @recursion_depth = @recursion_depth - 1;
END;//
DELIMITER ;

限制

  1. 为正在使用的模式运行存储过程的用户需要CREATE TEMPORARY TABLES权限。
  2. MySQL 仅支持最大递归深度 255,因此如果有大量外键链接(似乎不太可能),此方法将失败。
  3. 当前不支持“循环”/“循环”外键引用(例如,表 A 有一个指向 B 的外键,而表 B 有一个指向 A 的外键)当前不受支持,并且会导致无限循环。
  4. 它不是为在“实时”系统上使用而设计的:由于数据是递归删除的,如果在删除子记录和父记录之间添加了更多数据,以后的删除可能会失败。
于 2018-02-07T13:17:38.307 回答
0

看这个:

以什么顺序处理 ON DELETE CASCADE 约束?

但我认为您可以使用我的研究中的 ON DELETE CASCADE 。如果我错了,我相信社区会告诉我。如果可能的话,我相信你将不得不改变你的桌子。

另请参阅:

无法删除或更新父行:外键约束失败

于 2010-12-10T21:24:28.503 回答