SQL joins are used to combine data from two or more tables based on a common column.

The most common type of join is an inner join, which returns only the rows that have matching values in both tables.

Other types of joins include left join, right join, and full outer join,etc.

To perform a join, you use the JOIN keyword followed by the name of the table you want to join with.

You can also join more than two tables together by chaining multiple JOIN statements together.

When joining tables, it's important to use aliases to distinguish between the columns from each table.

Joining tables can also slow down query performance, especially if the tables are very large or the join conditions are complex.

When using a left join or right join, it's important to handle NULL values in the resulting table.