SQL-dynamic SQL, connection string and variable issues

 

Now we need to improve the paging storage process, because we have added the date-based get posts, sort by fields, and select sorting methods. In this case, you need to set some variables to receive these values from the application and connect them with the select and where strings.
Code:
Declare @ chengji int, @ SQL varchar (800)
Select @ chengji = 70
Set @ SQL = 'select * from Stu where score = '+ @ chengji
Print @ SQL

But when the problem arises, it always prompts that the varchar value 'select * from Stu where score = 'fails to be converted to the Data Type Int.

If changed:
Declare @ chengji varchar (800), @ SQL varchar (800)
Select @ chengji = 'A'
Set @ SQL = 'select * from Stu where score = ''' + @ chengji + ''''
Print @ SQL
You can.

========================================================== ======================
After verification: The cause and solution are as follows:

Because @ chengji is an integer, the integer cannot be directly connected to the character type with the plus sign (+), and must be converted to the character type before connection.
Try:
Declare @ chengji int, @ SQL varchar (800)
Select @ chengji = 70
Set @ SQL = 'select * from Stu where score = '+ rtrim (@ chengji)
Print @ SQL

Normal
Declare @ chengji int, @ SQL varchar (800)
Select @ chengji = 70
Set @ SQL = 'select * from Stu where score = '+ Cast (@ chengji as varchar (10 ))
Print @ SQL

Normal
Declare @ chengji int, @ SQL varchar (800)
Select @ chengji = 70
Set @ SQL = 'select * from Stu where score = '+ convert (varchar (10), @ chengji)
Print @ SQL
Normal