sql 语法错误（= 附近的语法不正确）

Question

Hello I am having a problem here. I wanted to read subjectname from a dynamic table name and the save it to a variable. but i am getting an error

DECLARE @retval varchar(200)   
DECLARE @sSQL nvarchar(500);
DECLARE @ParmDefinition nvarchar(500);
DECLARE @academicYear varchar(200) = '20212022';
Declare @subjectId varchar(200) = '202041962';

DECLARE @tablename nvarchar(50)   = 'abc' + CAST(@academicyear As varchar)
DECLARE @CONDITION NVARCHAR(128)
SET @CONDITION = 'WHERE [subjectid] = 202041962'

SELECT @sSQL = N'SELECT @retvalOUT = [subjectname] FROM ' + @tablename + @CONDITION;  
SET @ParmDefinition = N'@retvalOUT varchar OUTPUT';

EXEC sp_executesql @sSQL, @ParmDefinition, @retvalOUT=@retval OUTPUT;

SELECT @retval;

Answer 1

If you actually looked at the value of @sSQL eg by print ing it, you'll note it contains FROM abc20212022WHERE , therefore,

1. you are not delimiting your table names - use quotename()

2. you need a space between your table name and the where

3. you should always specify a length for a varchar value (you don't need to cast a variable when concatenating two strings but you should be consistent with your use of [n]varchar)

4. using concat to concatenate strings is easier and safer