Condition (SQL)
# Condition (SQL)

A relational database management system uses SQL conditions or expressions in WHERE clauses and in HAVING clauses to SELECT subsets of data.

## Types of condition

* Many conditions compare values for (for example) equality, inequality or similarity.
* The EXISTS condition uses the SQL standard keyword EXISTS to determine whether rows exist in a subquery result.

## Examples

To SELECT one row of data from a table called tab with a primary key column (pk) set to 100 — use the condition pk = 100:

To identify whether a table tab has rows of data with a duplicated column dk — use the condition having count(*) > 1:

