SQL Select Top

Using the SQL TOP keyword in a SELECT statement is equivalent to the LIMIT clause and differs only slightly – in its availability and functionality. Both are used to truncate the results of a query and return only a specified number of rows from its execution.

There is no SELECT TOP statement in some SQL databases, for example, both MySQL and PostgreSQL do not have it but can equivalently use LIMIT instead. Conversely, Microsoft SQL Server has the TOP keyword which is used instead of a LIMIT clause. Some other database types, for example Amazon Redshift, have both.

For a SQL database type, a query using a SELECT TOP statement has a nearly equivalent syntax to modifying query behavior with LIMIT. The two queries below would return the same result, one using TOP and the other LIMIT:

SELECT * FROM employees LIMIT 10;
SELECT TOP 10 * FROM employees;

One major difference of note is that TOP can be used together with the PERCENT keyword in order to retrieve a percentage of rows in a table, as opposed to specifying a number of rows.

We could retrieve the top 10 percent of data from the employees table using the below, even if we do not know the size of the table:

SELECT TOP 10 PERCENT * FROM employees;

Performing the equivalent in a SQL distribution without the TOP and PERCENT keywords would require calculating the number of rows in the table.