[SQL] 判斷第一碼為數字或是字母

VFP 中可以利用 ISDIGIT() 來判斷字串最左邊字元是否為數字，ISALPHA() 來判斷字串最左邊字元是否為英文字母，SQL Server內可以透過 LIKE 來達成。

CREATE FUNCTION [dbo].[ISDIGIT]
(
   @string as nvarchar(250)
)
RETURNS bit
AS
  BEGIN
    DECLARE @true bit
  
    IF @string LIKE '[0-9]%'
       SET @true = 1
    ELSE
       SET @true = 0
 
    RETURN @true
  END

CREATE FUNCTION [dbo].[ISALPHA]
(
   @string as nvarchar(250)
)
RETURNS bit
AS
  BEGIN
    DECLARE @true bit
 
    IF @string LIKE '[A-Z]%' -- 不區分大小寫
       SET @true = 1
    ELSE
       SET @true = 0
  
    RETURN @true
  END

SELECT Val,
    '數字判斷' = CASE WHEN dbo.ISDIGIT(Val) = 1 THEN '數字' ELSE '' END,
    '字母判斷' = CASE WHEN dbo.ISALPHA(Val) = 1 THEN '字母' ELSE '' END
FROM
     (
       SELECT '123' AS Val
       UNION ALL
       SELECT '456'
       UNION ALL
       SELECT 'ABC'
       UNION ALL
       SELECT 'def' -- 故意小寫
     ) AS T

• 結果

參考資料：
• LIKE in MSDN