Question

If I want to create a gender field in my table, how do I make sure that my database doesn’t accept any value apart from “M” or “F” ?

 $sqlCommand = "CREATE TABLE members (
             id int(11) NOT NULL auto_increment,
             ... 
             ...
             ...
             ...
             gender
             )";

Thank you

Answer 1

No triggers, no enums or other deamonic activities.

You can use a FOREIGN KEY to a reference table with just 2 rows:

CREATE TABLE Gender_Ref 
(   gender CHAR(1) NOT NULL,
    PRIMARY KEY (gender)
) ENGINE = InnoDB ;

INSERT INTO Gender_Ref (gender)
    VALUES
        ('F'), ('M')  ;

CREATE TABLE members 
(   id int(11) NOT NULL auto_increment,
     ... 
     ...
    gender CHAR(1) NOT NULL,
    PRIMARY KEY (id),
    FOREIGN KEY gender
        REFERENCES Gender_Ref (gender)
) ENGINE = InnoDB ;

It’s also good advice to “lock” the reference table so the applications code has only read access. (That’s usually good for most reference tables, and if you have an Admin application, you can of course give it write access as well to the reference tables).