mysql - mySQL：使用条件计算多个表中的唯一键

Question

我有一堆表（'table001'、'table002' 等），其中包含大量行和几列。

列是“id”（键）、“mode”（“ui”或“cmd”）和日期。

我想找出所有表中存在多少个唯一的 'id'，其模式设置为 'ui' 并且其日期小于 30 天前。

这是我当前的查询：

SELECT COUNT(*) FROM
(
    SELECT id FROM table001 WHERE mode="ui" AND date > (NOW() - INTERVAL 30 DAY)
    UNION
    SELECT id FROM table002 WHERE mode="ui" AND date > (NOW() - INTERVAL 30 DAY)
    UNION
    SELECT id FROM table003 WHERE mode="ui" AND date > (NOW() - INTERVAL 30 DAY)
    UNION
    [...etc etc for 30 tables]

) as t

这是这样做的正确方法吗？

标签： mysqlduplicatesunion

Answer 1

如果调用了所有 pk id，id那么您可以运行下面的存储过程，而无需静态键入所有表：

DELIMITER $$
CREATE PROCEDURE eval(IN dynamic_statement TEXT)
BEGIN
      SET @dynamic_statement := dynamic_statement;
      PREPARE prepared_statement FROM @dynamic_statement;
      EXECUTE prepared_statement;
      DEALLOCATE PREPARE prepared_statement;
  END$$
DELIMITER ;





DELIMITER $$
CREATE PROCEDURE sp_unique_id_count_across_all_tables()
BEGIN
    DECLARE var_key_fieldname VARCHAR(64) DEFAULT 'id';
    DECLARE var_tables_count INTEGER UNSIGNED;
    DECLARE var_index INTEGER UNSIGNED DEFAULT 1;
    DECLARE var_tablename_of_index VARCHAR(64);

    DROP TEMPORARY TABLE IF EXISTS tmp_tables_with_id;
    CREATE TEMPORARY TABLE tmp_tables_with_id
    SELECT
    #     *
        (@cnt := @cnt + 1) AS idx,
        TABLE_NAME AS tablename
    FROM information_schema.columns
    CROSS JOIN (SELECT @cnt := 0) A
    WHERE table_schema=SCHEMA()
    AND (COLUMN_NAME COLLATE utf8_unicode_ci) = (var_key_fieldname COLLATE utf8_unicode_ci)
    ;

    SET var_tables_count := (SELECT COUNT(0) FROM tmp_tables_with_id);

    DROP TEMPORARY TABLE IF EXISTS tmp_all_ids;
    CREATE TEMPORARY TABLE tmp_all_ids(
        id INTEGER NOT NULL UNIQUE
    );
    WHILE (var_index <= var_tables_count) DO
        SET var_tablename_of_index := (
            SELECT tablename
            FROM tmp_tables_with_id
            WHERE idx = var_index
            );
        CALL eval(CONCAT('
        INSERT IGNORE INTO tmp_all_ids(id)
        SELECT
            DISTINCT t.', var_key_fieldname, '
        FROM ', var_tablename_of_index,' t
        -- ON DUPLICATE KEY UPDATE id = t.', var_key_fieldname,'
        ;
        '));
        SET var_index := var_index + 1;
    END WHILE;
    SELECT COUNT(0) FROM tmp_all_ids;
END$$
DELIMITER;




DROP PROCEDURE IF EXISTS eval;
DROP PROCEDURE IF EXISTS sp_unique_id_count_across_all_tables;


CALL sp_unique_id_count_across_all_tables();