Access 中的大小写表达式 [英] Case expressions in Access
问题描述
您可以在 Access 中使用 case
表达式吗?我正在尝试确定 2 列的最大日期,但在以下代码中不断出现语法错误:
案例当 dbo_tbl_property.LASTSERVICEDATE >Contour_dates.[上次 CP12 日期]然后 dbo_tbl_property.LASTSERVICEDATEELSE Contour_dates.[最后 CP12 日期]结束为最大日期
您可以改用 IIF()
函数.
IIF(条件,valueiftrue,valueiffalse)
condition
是您要测试的值.valueiftrue
是条件计算结果为 TRUE 时返回的值.valueiffalse
是条件计算结果为 FALSE 时返回的值.
还有 切换
函数,当你有多个条件测试时更容易使用和理解:
Switch( expr-1, value-1 [, expr-2, value-2 ] ... [, expr-n, value-n ] )
<块引用>
Switch 函数参数列表由成对的表达式和值.表达式从左到右计算,并且与要计算为 True 的第一个表达式关联的值是回.如果零件未正确配对,则会出现运行时错误发生.例如,如果 expr-1 为 True,则 Switch 返回 value-1.如果expr-1 为 False,但 expr-2 为 True,Switch 返回 value-2,依此类推
Switch 在以下情况下返回 Null 值:
没有一个表达式为真.
第一个 True 表达式的对应值为 Null.
注意:Switch 计算所有表达式,即使它只返回其中一个.出于这个原因,你应该注意不良的副作用.例如,如果评估任何表达式导致除以零错误,发生错误.
Can you use case
expressions in Access? I'm trying to determine the max date form 2 columns but keep getting syntax errors in the following code:
CASE
WHEN dbo_tbl_property.LASTSERVICEDATE > Contour_dates.[Last CP12 Date]
THEN dbo_tbl_property.LASTSERVICEDATE
ELSE Contour_dates.[Last CP12 Date]
END AS MaxDate
You can use the IIF()
function instead.
IIF(condition, valueiftrue, valueiffalse)
condition
is the value that you want to test.valueiftrue
is the value that is returned if condition evaluates to TRUE.valueiffalse
is the value that is returned if condition evaluates to FALSE.
There is also the Switch
function which is easier to use and understand when you have multiple conditions to test:
Switch( expr-1, value-1 [, expr-2, value-2 ] … [, expr-n, value-n ] )
The Switch function argument list consists of pairs of expressions and values. The expressions are evaluated from left to right, and the value associated with the first expression to evaluate to True is returned. If the parts aren't properly paired, a run-time error occurs. For example, if expr-1 is True, Switch returns value-1. If expr-1 is False, but expr-2 is True, Switch returns value-2, and so on.
Switch returns a Null value if:
None of the expressions is True.
The first True expression has a corresponding value that is Null.
NOTE: Switch evaluates all of the expressions, even though it returns only one of them. For this reason, you should watch for undesirable side effects. For example, if the evaluation of any expression results in a division by zero error, an error occurs.
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