比LIKE语句更可变

Question

为什么这个工作：

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

同时意味着这个不行：

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

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

Answer 1

，使这项工作你需要使用动态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 

如果您不使用动态SQL，那么您需要提供列名，因为SQL解析器在解析查询时将查找列，如果找不到则会导致错误。

Answer 2

你需要使用动态SQL来实现你想要的。您当前的方法被评价为是这样的：

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

你真正想要的是更多这样的：

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

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

这将evalute到：

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