In a three-way join, the sql-expression consists of two conditions: one relates the first table to the second table and the other relates the second table to the third table.

A query-expression is one or more table-expressions. Multiple table expressions are linked by set operators. The following figure illustrates the relationship between table-expressions and ...

SQL is a convenient way to manage and query your data, but badly written queries can tie up your database. Here are seven common SQL traps and how to avoid them.