Tsql 如何在WHERE子句中使用CASE别名?
我试图将“val”放入where子句,但它返回错误:Tsql 如何在WHERE子句中使用CASE别名?,tsql,case,where,clause,Tsql,Case,Where,Clause,我试图将“val”放入where子句,但它返回错误: Select ff.FormID, ff.FieldID, ff.FieldName, ff.Title, ff.DefaultValue, fv.Value, val = case fv.Value when null then cast(ff.DefaultValue as nvarchar) else fv.Value end, ff.DataType from (SELECT FormID,
Select ff.FormID, ff.FieldID, ff.FieldName, ff.Title,
ff.DefaultValue, fv.Value,
val = case fv.Value when null then cast(ff.DefaultValue as nvarchar) else fv.Value end,
ff.DataType from
(SELECT FormID, FieldID, FieldName, Title, DataType, DefaultValue FROM FormFields where FormID = '766A38D8-8058-42C6-AC46-A18C00D3C1DC' and DEL = 0) as ff
left join
(select FormID, FieldID, Value from FormValues where FormID = '766A38D8-8058-42C6-AC46-A18C00D3C1DC' and ItemID = 'FD63CCA2-C95F-4AB4-B84B-A220017027E7' and DEL = 0) as fv
on ff.FormID = fv.FormID and ff.FieldID = fv.FieldID
where val is not null
Msg 207, Level 16, State 1, Line 9
Invalid column name 'val'.
感谢任何帮助:)不允许在where子句(sql server中)中使用别名,因为查询的逻辑执行顺序如下:
SELECT
之前执行子句的位置,这就是为什么您不能引用SELECT
子句中的别名
尝试:
如果要执行此操作,则需要使用子查询并将where子句放置在子查询之外,或者必须在where中重述大小写表达式。除非这是一个子查询并且您正在从中选择,否则您不能在其中引用别名。相反,您可以在where子句中使用val
中的case语句。它可能看起来很凌乱,但它确实起到了作用。请参阅“语句的逻辑处理顺序”<代码>其中
是步骤4。和“因为SELECT子句是步骤8,所以前面的子句不能引用该子句中定义的任何列别名或派生列”
Select ff.FormID, ff.FieldID, ff.FieldName, ff.Title,
ff.DefaultValue, fv.Value,
val = case fv.Value when null then cast(ff.DefaultValue as nvarchar) else fv.Value end,
ff.DataType from
(SELECT FormID, FieldID, FieldName, Title, DataType, DefaultValue FROM FormFields where FormID = '766A38D8-8058-42C6-AC46-A18C00D3C1DC' and DEL = 0) as ff
left join
(select FormID, FieldID, Value from FormValues where FormID = '766A38D8-8058-42C6-AC46-A18C00D3C1DC' and ItemID = 'FD63CCA2-C95F-4AB4-B84B-A220017027E7' and DEL = 0) as fv
on ff.FormID = fv.FormID and ff.FieldID = fv.FieldID
where case fv.Value when null then cast(ff.DefaultValue as nvarchar) else fv.Value end is not null