Microsoft Access - SQL command to add a constraint - sql

Question

I Am new in stackoverflow and whats worst is I am new to Microsoft Access. My homework
Assume the Part table has been created, but there are no integrity constraints. Create the necessary integrity constraint to ensure that the only allowable values for the Class field are AP, HW, and SG. Ensure that the PartNum field is the primary key and that the PartNum field in the OrderLine table is a foreign key that must match the primary key of the Part table.
So I know how to create this by using Microsoft Access by going to the Validation Rule and add validation for AP, HW, and SG. However, I need to also create the query to show how this is done.
My code:
ALTER TABLE Parts
ADD CONSTRAINT classRule
CHECK IN Class(AP, HW, SG)
;
My textbook has an example which is similar to what I just wrote above. When I run this I get a Constraint error. What am I doing wrong? Also, the foreign key and primary key have already been made so I just need to write the sql query to display my result. Any help is appreciated!

Answer 1

The CHECK clause exists but it's not a particularly good idea to use it because it can create issues in you application.
That being said, your constraint should work but there are a couple things:
You should avoid the use of the word Class as a field name. It's not a reserved word per se, but it's a VBA reserved word and while Access let you create that field, you may encounter strange problems elsewhere later.
As Brian said, you need to use single quotes for string literals in your CHECK
You can't create CONTRAINT with CHECK from the SQL Query Editor in Access, you'll get errors on the CHECK part every time you try.
Instead you need to execute the DDL SQL from VBA: just open the VBA (Alt+F11) then type the following in the Immediate Window (Ctrl-G if you don't see it), then press ENTER:
CurrentProject.Connection.Execute "ALTER TABLE Parts ADD CONSTRAINT ClassRule CHECK (Class IN ('AP', 'HW', 'SG'));"
If you don't get an error, then the constraint was properly executed, otherwise, double check that the syntax is correct, field names, parenthesis are properly balanced, and that the Part table is not open.

Answer 2

You probably want:
ALTER TABLE Parts
ADD CONSTRAINT classRule
CHECK (class in ('AP', 'HW', 'SG'));
There is a space between CONSTRAINT and the name
Put conditions within the () after the CHECK keyword
Put literals within single quotes, as this is what differentiates field names from values
Edit
Although the above is valid syntax, from what I'm reading you may not be able to add a check constraint in Access via writing out the SQL, at least not in the SQL view of query designer.
You can add a check constraint by going to Design View for the table of interest, then on the row representing the column of interest, type the following on the line for "Validation Rule":
in ('AP', 'HW', 'SG')
http://www.databaseskill.com/1942875/
"Note The check constraint statement can only be executed through the Jet OLE DB provider and ADO; it will return an error message if used though the Access SQL View user interface."
Above quote is from the URL I just provided.