MS SQL Server的COALESCE函数

MS SQL Server的COALESCE函数是从一系列表达式中返回第一个NOT NULL的值。

检查[B],[Q],[S],[T],[U]的值：

检查顺序[B]->[Q]->[S]->[T]->[U]，只要一遇上NOT NULL时，即刻返回。

IF OBJECT_ID('tempdb.dbo.#Part_summary') IS NOT NULL DROP TABLE #Part_summary

CREATE TABLE #Part_summary (    
    [Item] NVARCHAR(40),
    [B]DECIMAL(18,2),
    [Q]DECIMAL(18,2),
    [S]DECIMAL(18,2),
    [T]DECIMAL(18,2),
    [U]DECIMAL(18,2)
)

INSERT INTO #Part_summary ([Item],[B],[Q],[S],[T],[U])
VALUES ('098-SSSS1-WS0098-5526',NULl,NULl,500.00,NULl,NULl),
       ('54F-ART43-6545NN-2514',NULl,NULl,934.39,NULl,NULl),
       ('872-RTDE3-Q459PW-2323',NULl,346.43,NULl,452.44,NULl),
       ('B78-F1H2Y-5456UD-2530',234.22,NULl,NULl,115.06,NULl),
       ('I32-GG443-QT0098-0001',NULl,NULl,423.65,NULl,NULl),
       ('I38-AA321-WS0098-0506',470.87,NULl,NULl,NULl,345.41),
       ('K38-12321-5456UD-3493',200.28,NULl,NULl,398.55,NULl),
       ('PO0-7G7G7-JJY098-0077',NULl,871.33,543.00,NULl,NULl),
       ('RVC-43ASE-H43QWW-9753',NULl,564.96,NULl,NULl,555.19),
       ('X3C-SDEWE-3ER808-8764',NULl,607.88,NULl,NULl,NULl)

SELECT [Item],[B],[Q],[S],[T],[U]  FROM #Part_summary

SELECT [Item],COALESCE([B],[Q],[S],[T],[U]) AS [result] FROM #Part_summary

再列一个例子：

IF OBJECT_ID('tempdb.dbo.#Part_summary') IS NOT NULL DROP TABLE #Part_summary

CREATE TABLE #Part_summary (    
    [Item] NVARCHAR(40),
    [B]DECIMAL(18,2),
    [Q]DECIMAL(18,2),
    [S]DECIMAL(18,2),
    [T]DECIMAL(18,2),
    [U]DECIMAL(18,2)
)

INSERT INTO #Part_summary ([Item],[B],[Q],[S],[T],[U])
VALUES ('54F-ART43-6545NN-2514',NULl,NULl,NULl,NULl,934.39),
       ('872-RTDE3-Q459PW-2323',NULl,NULl,NULl,452.44,NULl),
       ('B78-F1H2Y-5456UD-2530',NULl,NULl,115.06,NULl,NULl),
       ('I32-GG443-QT0098-0001',NULl,607.88,NULl,NULl,NULl),
       ('I38-AA321-WS0098-0506',470.87,NULl,NULl,NULl,NULl)

SELECT [Item],[B],[Q],[S],[T],[U]  FROM #Part_summary

SELECT [Item],COALESCE([B],[Q],[S],[T],[U]) AS [result] FROM #Part_summary