与OR子句的SQL查询性能

Question

这个SQL查询需要10秒：

SELECT * FROM A a
JOIN B b on a.idB = b.idB
JOIN C c on b.idC = c.idC
JOIN D d on c.idD = d.idD
JOIN E e  ON((e.perimeterId = a.idA AND e.level = 3) 
          OR (e.perimeterId = b.idB AND e.level = 2) 
          OR (e.perimeterId = c.idC AND e.level = 1)
          OR (e.perimeterId = d.idD AND e.level = 0))

更改或与CASE子句，查询需要3秒：

SELECT * FROM A a
JOIN B b on a.idB = b.idB
JOIN C c on b.idC = c.idC
JOIN D d on c.idD = d.idD
JOIN E e  ON (
               CASE e.level
                    when 3 then a.idA
                    when 2 then b.idB
                    when 1 then c.idC
                    when 0 then d.idD
               END
             ) = e.perimeterId 

如果我执行有独立的OR子句的查询时，查询立即执行全无OR子句：

SELECT * FROM A a
JOIN B b on a.idB = b.idB
JOIN C c on b.idC = c.idC
JOIN D d on c.idD = d.idD
JOIN E e  ON (e.perimeterId = a.idX AND e.level = X) 

如何重写我的查询将立即执行或高性能可能吗？

Answer 1

您只希望从e列，所以我会用exists写：

SELECT e.*
FROM E e
WHERE EXISTS (SELECT 1
              FROM a
              WHERE e.perimeterId = a.idA AND e.level = 3
             ) OR
      EXISTS (SELECT 1
              FROM a JOIN
                   b
                   ON a.idB = b.idB
              WHERE e.perimeterId = b.idA AND e.level = 2
             ) OR
      EXISTS (SELECT 1
              FROM a JOIN
                   b
                   ON a.idB = b.idB JOIN
                   c
                   ON c.idC = b.idC
              WHERE e.perimeterId = c.idA AND e.level = 1
             ) OR
      EXISTS (SELECT 1
              FROM a JOIN
                   b
                   ON a.idB = b.idB JOIN
                   c
                   ON c.idC = b.idC JOIN
                   d
                   ON d.idD = c.idD
              WHERE e.perimeterId = d.idA AND e.level = 0
             );

我不知道该JOINs需要在子查询100％，但我已经离开他们，无论如何。

Answer 2

1）上a.idB，b.idB，b.idC，c.idC，c.idD，d.idD，e.perimeterId，E.LEVEL创建索引

2）试试这个

SELECT * FROM A a
JOIN B b on a.idB = b.idB
JOIN C c on b.idC = c.idC
JOIN D d on c.idD = d.idD
JOIN E e  ON(e.perimeterId = a.idA AND e.level = 3) 
UNION ALL
SELECT * FROM A a
JOIN B b on a.idB = b.idB
JOIN C c on b.idC = c.idC
JOIN D d on c.idD = d.idD
JOIN E e  ON(e.perimeterId = a.idB AND e.level = 2) 
UNION ALL
SELECT * FROM A a
JOIN B b on a.idB = b.idB
JOIN C c on b.idC = c.idC
JOIN D d on c.idD = d.idD
JOIN E e  ON(e.perimeterId = a.idC AND e.level = 1) 
UNION ALL
SELECT * FROM A a
JOIN B b on a.idB = b.idB
JOIN C c on b.idC = c.idC
JOIN D d on c.idD = d.idD
JOIN E e  ON(e.perimeterId = a.idD AND e.level = 0)