Question

我知道IN，NOT in in mysql查询（不推荐使用）不是性能明智的，但这是我需要实现的。还有其他方法可以更好地实现相同的结果吗？ Loc_table是具有id和name的用户列表，表1和2是两个不同的任务表，如果用户完成该特定表的任务，则我在其中注册其他任务（boolean yes no）。下面的查询工作正常，但速度很慢。任何帮助将不胜感激。

loc = mysql_query("SELECT loc_id, name,
    CASE
    WHEN loc_id IN (SELECT user_id FROM table 1 WHERE done = 0 GROUP BY loc_id) THEN 1 ELSE 0
    END AS active_in_1,
    CASE
    WHEN loc_id IN (SELECT user_id FROM table2 WHERE done = 0 GROUP BY loc_id) THEN 1 ELSE 0
    END AS active_in_2
    FROM loc_table L LEFT JOIN table_2 C ON C.loc_id = L.loc_id LEFT JOIN table_1 A ON A.loc_id = L.loc_id
    WHERE C.done = 0 OR A.done = 0 GROUP BY loc_id ORDER BY name") or die (mysql_error());

Answer 1

您不需要在查询中使用子选择

SELECT loc_id, name,
    CASE
    WHEN A.loc_id is null THEN 0 ELSE 1
    END AS active_in_1,
    CASE
    WHEN c.loc_id is null THEN 0 ELSE 1
    END AS active_in_1        FROM loc_table L LEFT JOIN table_2 C ON C.loc_id = L.loc_id LEFT JOIN table_1 A ON A.loc_id = L.loc_id
    WHERE C.done = 0 OR A.done = 0

的群组功能在哪里

 GROUP BY loc_id ORDER BY name

Answer 2

写好另一个查询我偶然发现了解决方案，它将执行时间从4秒减少到40毫秒

select L.loc_id ,L.name,
CASE
WHEN (SELECT count(*) from table_1 where user_id = L.loc_id and done = 0) > 0 THEN 1 ELSE 0
END as active_in_1,
CASE
WHEN (SELECT count(*) from table_2 where user_id = L.loc_id and done = 0) > 0 THEN 1 ELSE 0
END as active_in_2
FROM loc_table L group by loc_id
HAVING active_in_1 != 0 OR active_in_2 != 0
ORDER BY name;

我如何优化此查询？

2 个答案: