sql查询的未知执行时间行为

案例1:

SELECT Column1, 
       Cloumn2, 
       Cloumn3 
  FROM TableName
 WHERE Column3 In (SELECT COL3 
                     FROM #TempTable)

案例2:

DECLARE @valueClo3 varchar(50)
    set @valueClo3   = 'AnyValue'
SELECT Column1, 
       Cloumn2, 
       Cloumn3 
  FROM TableName
 WHERE Column3 In (@valueClo3)

案例1耗时太长(约3分钟),而案例2仅需10秒。 #TempTable 只有一个值 'AnyValue'