向查询添加OR条件会降低查询速度

Question

我向查询添加了OR条件，查询执行时间从小于0.5秒到达15+秒。在where子句中使用的所有列都被编入索引。想知道如何优化这个查询。

SELECT SQL_NO_CACHE COUNT(DISTINCT wo.id) AS totrows 
FROM wo 

LEFT JOIN wu 
ON wu.id = wo.id 

LEFT JOIN bu 
ON bu.id = wu.id 

LEFT JOIN ub 
ON ub.uid = bu.id 

JOIN u 
ON u.id = wo.created_by 

LEFT JOIN ws 
ON ws.wo_id = wo.id, b 

WHERE (wo.bid = '13' 
AND (wo.created_by IN('2506') OR wo.uid IN('2506')) 
AND wo.status != 5 
AND (wo.uid = '' || wu.uid in ('406', 0) || wo.uid IS NULL) 
AND wo.ut = 0 
AND ((wo.wt = 'unit' AND (wo.archive != 1 OR wo.archive IS NULL)) OR wo.wt = 'common')) OR (ws.uid = 2506) 

删除OR (ws.uid = 2506)使查询速度非常快。

Answer 1

我结束了这样使用SELECT COUNT(*) FROM (Query1 union Query2)。目前看起来不错。

SELECT COUNT(*) AS totrows FROM (
    SELECT SQL_NO_CACHE COUNT(DISTINCT wo.id) AS totrows 
    FROM wo 

    LEFT JOIN wu 
    ON wu.id = wo.id 

    LEFT JOIN bu 
    ON bu.id = wu.id 

    LEFT JOIN ub 
    ON ub.uid = bu.id 

    JOIN u 
    ON u.id = wo.created_by 

    LEFT JOIN ws 
    ON ws.wo_id = wo.id 

    WHERE (wo.bid = '13' 
    AND (wo.created_by IN('2506') OR wo.uid IN('2506')) 
    AND wo.status != 5 
    AND (wo.uid = '' || wu.uid in ('406', 0) || wo.uid IS NULL) 
    AND wo.ut = 0 
    AND ((wo.wt = 'unit' AND (wo.archive != 1 OR wo.archive IS NULL)) OR wo.wt = 'common')) OR (ws.uid = 2506) 

    UNION 

    select DISTINCT wo.id from wo LEFT JOIN ws ON ws.wo_id = wo.id WHERE ws.uid = 2506 

) AS T