使用 2 个键加速连接

Question

我可以加快速度吗？

CREATE TABLE TEST AS 
SELECT t1.Tech, t2.Coloar,t2.Car from Table1 t1 
INNER JOIN Table2 t2 on (t1.ID = t2.ID AND t1.IT = t2.IT AND t1.LIFI = t2.LIFI) OR (t1.RA = t2.RA) 
where...

如果我用

创建 table

(t1.ID = t2.ID AND t1.IT = t2.IT AND t1.LIFI = t2.LIFI)

或者用这个键

(t1.RA = t2.RA)

这需要几秒钟，但两者加起来只需要几分钟，而且我有更多更大的 table 要创建，有时我需要 LEFT JOIN 这个密钥对，比如

CREATE TABLE...
INNER JOIN...
LEFT JOIN on (t1.ID = t2.ID AND t1.IT = t2.IT AND t1.LIFI = t2.LIFI) OR (t1.RA = t2.RA)

Answer 1

试试这个

CREATE TABLE TEST AS 
select t1.Tech, t2.Coloar,t2.Car
From Table1  t1
left join Table2 t2 on (case when t1.RA = t2.RA then 1 when t1.ID = t2.ID AND t1.IT = t2.IT AND t1.LIFI = t2.LIFI then 1 else 0 end = 1)

Answer 2

从 ON 子句中删除 OR：

CREATE TABLE TEST AS 
    SELECT t1.Tech,
           COALESCE(t2.Color, tt2.Color),
           COLAESCE(t2.Car, tt2.Car)
    FROM Table1 t1 LEFT JOIN
         Table2 t2 
         ON t1.ID = t2.ID AND t1.IT = t2.IT AND t1.LIFI = t2.LIFI LEFT JOIN
         Table2 tt2
         ON t1.RA = tt2.RA AND t2.ID IS NULL
     WHERE (t2.ID IS NOT NULL OR tt2.ID IS NOT NULL) AND
           ...

这应该能够为两个连接利用适当的索引。

使用 2 个键加速连接

Speed up a join with 2 keys

sql

postgresql

join

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