I am a new user trying to learn mysql (using InnoDB tables, mysql version 3.23.54) and to create a useful database for a project I am working on. In trying to understand how to use foreign keys effectively, I studied examples at http://sqlzoo.net - "A Gentle Introduction to SQL"
I am trying to understand why some columns which refer to other tables are defined as foreign keys and why others are not. Basically, what is the difference between a column which refers to another table but is not explicitly a "foreign key" and one which is? I would be grateful if anyone could help me to understand this distinction. From one of the sample databases, here is a create table statement which includes both types: CREATE TABLE order_line ( order_ref INTEGER NOT NULL REFERENCES dress_order ,line_no INTEGER NOT NULL ,ol_style INTEGER REFERENCES garment ,ol_size INTEGER NOT NULL ,ol_material INTEGER REFERENCES material ,PRIMARY KEY (order_ref, line_no) ,FOREIGN KEY (ol_style, ol_size) REFERENCES quantities ); I already discovered that in order for me to make this work, I had to insert a line creating indexes: INDEX (ol_style, ol_size), before the foreign key definition and that I had to explicitly identify the columns in the referenced table for the foreign keys to be created: FOREIGN KEY (ol_style, ol_size) REFERENCES quantities (style_q, size_q) Thanks very much for any help. sorry if I'm asking in the wrong place... RB -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
