Sams Teach Yourself SQL in 10 Minutes

Using Joins and Join Conditions

Before I wrap up our two lesson discussion on joins, I think it is worthwhile to summarize some key points regarding joins and their use:

• Pay careful attention to the type of join being used. More often than not, you'll want an inner join, but there are often valid uses for outer joins, too.

• Check your DBMSs documentation for the exact join syntax it supports. (Most DBMSs use one of the forms of syntax described in these two lessons.)

• Make sure you use the correct join condition (regardless of the syntax being used), or you'll return incorrect data.

• Make sure you always provide a join condition, or you'll end up with the Cartesian Product.

• You may include multiple tables in a join and even have different join types ...