An SQL join clause combines columns from one or more tables in a relational database . It creates a set that can be saved as a table or used as it is. A JOIN is a means for combining columns from one (self-table) or more tables by using values common to each. ANSI -standard SQL specifies five types of JOIN : INNER , LEFT OUTER , RIGHT OUTER , FULL OUTER and CROSS . As a special case, a table (base table, view , or joined table) can JOIN to itself in a self-join .