mysql - 需要优化 SQL 查询 - 执行需要花费大量时间

Question

我们有一个下面的查询，执行大约需要 6-8 秒。 记录总数:522954

(SELECT 
        * 
      FROM
        tbl_insights_copy
      WHERE insightscat = 21 
        AND submitedon >= UNIX_TIMESTAMP(DATE_SUB(NOW(), INTERVAL 30 DAY)) 
      ORDER BY submitedon DESC 
      LIMIT 5) 
      UNION
      (SELECT 
        * 
      FROM
        tbl_insights_copy 
      WHERE insightscat = 22 
        AND submitedon >= UNIX_TIMESTAMP(DATE_SUB(NOW(), INTERVAL 30 DAY)) 
      ORDER BY submitedon DESC 
      LIMIT 5) 
      UNION
      (SELECT 
        * 
      FROM
        tbl_insights_copy 
      WHERE insightscat = 23 
        AND submitedon >= UNIX_TIMESTAMP(DATE_SUB(NOW(), INTERVAL 30 DAY)) 
      ORDER BY submitedon DESC 
      LIMIT 5) 
      UNION
      (SELECT 
        * 
      FROM
        tbl_insights_copy 
      WHERE insightscat = 24 
        AND submitedon >= UNIX_TIMESTAMP(DATE_SUB(NOW(), INTERVAL 30 DAY)) 
      ORDER BY submitedon DESC 
      LIMIT 5)

有人可以帮助优化此查询以减少执行时间。 提前致谢。

Answer 1

您在一个选择和另一个选择之间唯一改变的是 insightscat 列的过滤器值，我不确定这是否是您想要的，但是......

您可以为此尝试使用IN 指令。示例:

SELECT 
        * 
FROM
        tbl_insights_copy 
      WHERE insightscat in (20,21,22,23,24)
        AND submitedon >= UNIX_TIMESTAMP(DATE_SUB(NOW(), INTERVAL 30 DAY)) 
      ORDER BY submitedon DESC