Beginning SQL

Chapter 4
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Finally, you do the same thing for the Attendance table, beginning with the NOT NULL constraint:
ALTER TABLE Attendance
ALTER COLUMN LocationId int NOT NULL;
ALTER TABLE Attendance
ALTER COLUMN MemberId int NOT NULL;
Again, for Oracle or MySQL, change the code to the following:
ALTER TABLE Attendance
MODIFY LocationId int NOT NULL;
ALTER TABLE Attendance
MODIFY MemberId int NOT NULL;
Then you add the PRIMARY KEY constraint:
ALTER TABLE Attendance
ADD CONSTRAINT attendance_pk PRIMARY KEY (LocationId, MemberId);
Your next objective in improving the database is to prevent columns containing NULL values where
necessary. Good practice is to add the NOT NULL constraint when creating the table. For example, if
the FilmName column contains no value, it makes the whole record rather pointless, as the name is so
essential. On the other hand, having a missing rating is not as much of a problem. Begin by adding a NOT
NULL constraint to the FilmName column. In MS Access or SQL Server, use the following code:
ALTER TABLE Films
ALTER COLUMN FilmName varchar(100) NOT NULL;
In Oracle or MySQL, type this statement:
ALTER TABLE Films
MODIFY FilmName varchar(100) NOT NULL;
Finally, in IBM DB2, use the following SQL:
CREATE TABLE TempFilms
(
FilmId integer NOT NULL,
FilmName varchar(100),
YearReleased integer,
PlotSummary varchar(2000),
AvailableOnDVD char(1),
Rating integer,
CategoryId integer
);
INSERT INTO TempFilms
SELECT * FROM Films;
DROP TABLE Films;
CREATE TABLE Films