Question

我有以下3张桌子。

 PROP_MASTER
--------------------
    BORO
    BLOCK
    LOT
    COL1
    COL2
    COL3

    TABLE2
-------------
    BORO
    BLOCK
    LOT
    COL4

    TABLE3
-------------
    BORO
    BLOCK
    LOT
    COL5

在一个查询中我想得到

Boro
Block
Lot
COL1
COL2
COL3
COL4 
COL5

但是，如果两个表2中的同一个BORO，BLOCK和LOT不存在记录，则COL4应该返回0，如果表3中不存在记录，则COL5应该为零。

我如何加入这3个表。

Select B.BORO,B.BLOCK,B.LOT,B.COL1,B.COL2,B.COL3
FROM PROP_MASTER B, TABLE2 T2, TABLE3 T3
WHERE B.BORO=T2.BORO AND B.BORO=T3.BORO AND
B.BLOCK=T2.BLOCK AND B.BLOCK=T3.BLOCK AND
B.LOT=T3.LOT AND B.LOT=T3.LOT

Answer 1

我认为您最好的方法是根据共同的属性（BORO，BLOCK和LOT）将LEFT JOIN Table2和Table3放入您的PROP_MASTER，然后使用COALESCE：

SELECT
    PROP_MASTER.BORO,
    PROP_MASTER.BLOCK,
    PROP_MASTER.LOT,
    PROP_MASTER.COL1,
    PROP_MASTER.COL2,
    PROP_MASTER.COL3,
    COALESCE(TABLE2.COL4, 0) AS COL4,
    COALESCE(TABLE3.COL5, 0) AS COL5
FROM PROP_MASTER
    LEFT JOIN TABLE2 ON
        TABLE2.BORO = PROP_MASTER.BORO
        AND TABLE2.BLOCK = PROP_MASTER.BLOCK
        AND TABLE2.LOT = PROP_MASTER.LOT
    LEFT JOIN TABLE3 ON
        TABLE3.BORO = PROP_MASTER.BORO
        AND TABLE3.BLOCK = PROP_MASTER.BLOCK
        AND TABLE3.LOT = PROP_MASTER.LOT

Answer 2

参加工会

select col from PROP_MASTER
union
select col from TABLE2
union
select col from TABLE3

Answer 3

您可以使用此

Select B.BORO,B.BLOCK,B.LOT,B.COL1,B.COL2,B.COL3,T2.COL4,T3.COL5
FROM PROP_MASTER B  
LEFT join  TABLE2 T2 ON B.BORO=T2.BORO  AND B.BLOCK=T2.BLOCK AND B.LOT=T2.LOT
LEFT join  TABLE3 T3 ON B.BORO=T3.BORO  AND B.BLOCK=T3.BLOCK AND B.LOT=T3.LOT
WHERE 
(T2.BORO IS NULL and T2.BLOCK IS NULL and T2.LOT IS NULL) OR 
(T3.BORO IS NULL and T3.BLOCK IS NULL and T3.LOT IS NULL)

连接3个表，如果在2个表中的任何一个表中均未找到值，则为列返回0

3 个答案: