在 SQL 中，主表应与多列的查找表匹配

Question

主表应该与给定列的查找表匹配，如果它不匹配并且查找表有任何空值，那么它应该与空值匹配（这里 null = 任何值）

场景

CREATE TABLE dbo.MAIN_TABLE (
NAMEID VARCHAR(50) NOT NULL,
COL1 VARCHAR(50) NULL,
COL2 VARCHAR(50) NULL,
COL3 VARCHAR(50) NULL,
COL4 VARCHAR(50) NULL,
CONSTRAINT PK_MAIN_TABLE PRIMARY KEY (NAMEID)
)

CREATE TABLE dbo.LOOKUP_TABLE (
COL1 VARCHAR(50) NULL,
COL2 VARCHAR(50) NULL,
COL3 VARCHAR(50) NULL,
COL4 VARCHAR(50) NULL,
RES_COL VARCHAR(50) NOT NULL
)

TRUNCATE TABLE dbo.LOOKUP_TABLE
INSERT INTO dbo.LOOKUP_TABLE VALUES('AA','BB', 'CC', NULL, 'Rule1')
INSERT INTO dbo.LOOKUP_TABLE VALUES('AA','BB', NULL, NULL, 'Rule2')
INSERT INTO dbo.LOOKUP_TABLE VALUES('AA',NULL, NULL, NULL, 'Rule3')
INSERT INTO dbo.LOOKUP_TABLE VALUES(NULL,NULL, NULL, NULL, 'Rule4')

TRUNCATE TABLE dbo.MAIN_TABLE
INSERT INTO dbo.MAIN_TABLE VALUES('NameId1','AA','BB', 'CC', 'DD' )
INSERT INTO dbo.MAIN_TABLE VALUES('NameId2','AA','BB', 'CC', NULL )
INSERT INTO dbo.MAIN_TABLE VALUES('NameId3','AA','BB', NULL, NULL )
INSERT INTO dbo.MAIN_TABLE VALUES('NameId4','AA', NULL, NULL, NULL )

INSERT INTO dbo.MAIN_TABLE VALUES('NameId5',NULL,'BB', 'CC', 'DD' )
INSERT INTO dbo.MAIN_TABLE VALUES('NameId6',NULL,NULL, 'CC', 'DD' )

预期结果

NAMEID  |  RES_COL
-----------------
NameId1 | Rule1
NameId2 | Rule1
NameId3 | Rule2
NameId4 | Rule3
NameId5 | Rule4
NameId6 | Rule4

我尝试了类似下面的查询，但它返回的重复行包含所有其他值

SELECT MN.NAMEID, MAP.RES_COL  FROM MAIN_TABLE MN
CROSS APPLY
(
  SELECT * FROM LOOKUP_TABLE LKP
  WHERE  
   ( CHECKSUM(MN.COL1) = CHECKSUM(LKP.COL1) OR LKP.COL1 IS NULL )
  AND
   ( CHECKSUM(MN.COL2) = CHECKSUM(LKP.COL2) OR LKP.COL2 IS NULL)
  AND
   ( CHECKSUM(MN.COL3) = CHECKSUM(LKP.COL3) OR LKP.COL3 IS NULL)
  AND
   ( CHECKSUM(MN.COL4) = CHECKSUM(LKP.COL4) OR LKP.COL4 IS NULL )
) MAP

ORDER BY MN.NAMEID ASC

Answer 1

由于 NULL = 匹配任何规则，您会获得多个匹配项。所以对于任何名称，Rule4 肯定会匹配，因为它对于所有列都是 NULL

如果您只想要最佳匹配，请使用 TOP 1 和 ORDER BY

SELECT  *
FROM    dbo.MAIN_TABLE m
        OUTER APPLY
        (
            SELECT  TOP 1 *
            FROM    dbo.LOOKUP_TABLE l
            WHERE   (l.COL1 = m.COL1 OR l.COL1 IS NULL)
            AND     (l.COL2 = m.COL2 OR l.COL2 IS NULL)
            AND     (l.COL3 = m.COL3 OR l.COL3 IS NULL)
            AND     (l.COL4 = m.COL4 OR l.COL4 IS NULL)
            ORDER BY 
                CASE WHEN l.COL1 IS NOT NULL THEN 1 ELSE 2 END
            +   CASE WHEN l.COL2 IS NOT NULL THEN 1 ELSE 2 END
            +   CASE WHEN l.COL3 IS NOT NULL THEN 1 ELSE 2 END
            +   CASE WHEN l.COL4 IS NOT NULL THEN 1 ELSE 2 END
        ) l

您使用 CHECKSUM() 而不是简单相等的 = 的任何特殊原因？