我正在尝试执行下一个查询
DECLARE @ponumber varchar(50)
DECLARE @gcas varchar(50)
SET @ponumber = '3864_ab03963'
SET @gcas = '81332119.'
EXEC(N'SELECT * FROM tCleanOrderTracking_prod
WHERE [PO number] = ' + @ponumber + ' AND [GCAS] = ' + @gcas)
我收到一条错误消息
Msg 102, Level 15, State 1, Line 1
Incorrect syntax near '_ab03963'.
我做错了什么?