Question

查询：

UPDATE empPac
    SET quantityLimit = allocation,
        allocationStart = '"&allocationStart&"',
        nextUpdate = DATEADD(mm, allocationMonths, "&allocationStart&"),
        lastUpdate = GETDATE(),
        quantityIssued = 0,
        quantityShipped = 0
    WHERE allocation IS NOT NULL AND
          allocationMonths <> 0 AND
          (nextUpdate <= DATEADD(mm, "&checkCondition&", GETDATE()) OR
           nextUpdate IS NULL) AND
          empIdent in (select empIdent
                       from employee
                       where custIdent='"&custIdent&"')

我想要做的是向SET quantityLimit = allocation添加一个条件语句，这样我就不想拥有WHERE allocation IS NOT NULL，而是希望它有一个条件语句，例如SET quantityLimit = ((allocation IS NULL) ? 0 : allocation)

Answer 1

您可以使用ISNULL()：

SET quantityLimit = ISNULL(allocation, 0)

其他数据库的等效函数为Oracle NVL()和MySQL IFNULL()和SQLite

如果您想提高代码的可移植性，那么您真正应该使用的是COALESCE()。 COALESCE是SQL-92 standard的一部分，并在RDBMS之间得到广泛支持。

Answer 2

您使用什么数据库？例如，在oracle sql中，您可以编写case when allocation is null then 0 else allocation end或nvl (allocation, 0)或coalesce (allocation, 0)

而case syntax in MSSQL与Oracle中的相同。

Answer 3

这是TSQL（MSSQL）方式：

SET quantityLimit = isnull(allocation,0)

...替代

SET quantityLimit = CASE WHEN allocation is null THEN 0 ELSE allocation END
--This one might be handy if you wanted to check for more than just null values.  Such as:
----...CASE WHEN allocation is null THEN 0 WHEN some_other_value THEN 1 WHEN ... THEN ... ELSE allocation END

SET quantityLimit = coalesce(allocation,0)
--This one gives you the first non-null value it finds, given a list of places to look.  Such as:
----...coalesce(allocation,some_other_field,some_nuther_field,...,0)

在UPDATE中添加条件语句

3 个答案: