我有一个知道用逗号分割字符串的函数：
SELECT * FROM dbo.SplitStrings('15,29')
返回
Item
15
29
我还有一个知道用逗号连接字符串的函数：
DECLARE @table AS SmallStrings
INSERT INTO @table VALUES ('a'),('b'),('c')
SELECT dbo.JoinStrings(@table) Joined
返回
Joined
a,b,c
现在我想分割一个字符串，修改每个项目并将它们连接起来。我也可以这样做：
DECLARE @tmp SmallStrings
INSERT INTO @tmp SELECT dbo.DayOfMonthExprToCron2(Item) Item FROM dbo.SplitStrings('15,29')
SELECT dbo.JoinStrings(@tmp) Result
返回
Result
15,L
现在我想知道我是否可以将SELECT dbo.DayOfMonthExprToCron2(Item) Item FROM dbo.SplitStrings('15,29')的结果直接传递给dbo.JoinStrings
我尝试过但失败了 - 我的卑微尝试甚至都没有编译。
天真的人：
SELECT dbo.JoinStrings(SELECT dbo.DayOfMonthExprToCron2(Item) Item FROM dbo.SplitStrings('15,29')) Result
结果
Msg 156, Level 15, State 1, Line 1
Incorrect syntax near the keyword 'SELECT'.
Msg 102, Level 15, State 1, Line 1
Incorrect syntax near ')'.
另一次尝试（使用双括号）：
SELECT dbo.JoinStrings((SELECT dbo.DayOfMonthExprToCron2(Item) Item FROM dbo.SplitStrings('15,29'))) Result
结果
Msg 206, Level 16, State 2, Line 1
Operand type clash: nvarchar is incompatible with SmallStrings
我意识到代码是必需的，所以这就是：
CREATE FUNCTION [dbo].[SplitStrings](@List NVARCHAR(4000))
RETURNS TABLE
WITH SCHEMABINDING
AS
RETURN
(
SELECT Item = y.i.value('(./text())[1]', 'nvarchar(4000)')
FROM (
SELECT x = CONVERT(XML, '<i>' + REPLACE(@List, ',', '</i><i>') + '</i>').query('.')
) AS a
CROSS APPLY x.nodes('i') AS y(i)
);
CREATE FUNCTION [dbo].[JoinStrings](@strings SmallStrings READONLY)
RETURNS NVARCHAR(4000)
AS
BEGIN
DECLARE @res NVARCHAR(32)
SELECT @res = COALESCE(@res + ',', '') + Item
FROM @strings
WHERE Item IS NOT NULL
RETURN @res
END
CREATE TYPE [dbo].[SmallStrings] AS TABLE([Item] [nvarchar](5) NULL)
CREATE FUNCTION [dbo].[DayOfMonthExprToCron2](@dayOfMonthExpr NVARCHAR(32))
RETURNS NVARCHAR(32)
AS
BEGIN
DECLARE @dayOfMonth INT = CAST(@dayOfMonthExpr AS INT)
RETURN CASE WHEN @dayOfMonth < 29 THEN @dayOfMonthExpr ELSE 'L' END
END