比LIKE語句更可變

Question

爲什麼這個工作：

SELECT * FROM Companies WHERE CompanyCode LIKE '%' AND BusinessUnitShortName LIKE 'CO%' 

同時意味着這個不行：

DECLARE @WHERECondition NVARCHAR(200) = '' 
SET @WHERECondition = '''%'' AND BusinessUnitShortName LIKE ''CO%''' 

SELECT * FROM Companies WHERE CompanyCode LIKE @WHERECondition 
SELECT @WHERECondition 

Answer 1

，使這項工作你需要使用動態SQL，如

DECLARE @WHERECondition NVARCHAR(200) = '' 
SET @WHERECondition = '''%'' AND BusinessUnitShortName LIKE ''CO%''' 
declare @sql nvarchar(Max) 

Set @sql='SELECT * FROM Companies WHERE CompanyCode LIKE'+@WHERECondition 

exec sp_executesql @sql 

如果您不使用動態SQL，那麼您需要提供列名，因爲SQL解析器在解析查詢時將查找列，如果找不到則會導致錯誤。

Answer 2

你需要使用動態SQL來實現你想要的。您當前的方法被評價爲是這樣的：

SELECT * 
FROM Companies 
WHERE CompanyCode LIKE '''%'' AND BusinessUnitShortName LIKE ''CO%''' 

你真正想要的是更多這樣的：

DECLARE @sql NVARCHAR(MAX) = '' 
DECLARE @WHERECondition = '''%'' AND BusinessUnitShortName LIKE ''CO%''' 

SET @sql = 'SELECT * FROM Companies WHERE CompanyCode LIKE ' + @WHERECondition 
EXEC(@sql); 

這將evalute到：

SELECT * FROM Companies WHERE CompanyCode LIKE '%' AND BusinessUnitShortName LIKE 'CO%'