WITH keyword

Name one or several sub-queries to be used within the main query.

This clause makes it easy to simplify large or complex statements which involve sub-queries, particularly when such sub-queries are used several times.

Syntax

Where:

• subQueryName is the alias for the sub-query
• subQuery is a SQL query (e.g SELECT * FROM table)
• mainQuery is the main SQL query which involves the subQuery using its alias.

Examples

Single alias

WITH first_10_users AS (SELECT * FROM users limit 10)

SELECT user_name FROM first_10_users;

Using recursively

WITH first_10_users AS (SELECT * FROM users limit 10),

first_5_users AS (SELECT * FROM first_10_users limit 5)

SELECT user_name FROM first_5_users;

Flag whether individual trips are longer or shorter than average

WITH avg_distance AS (SELECT avg(trip_distance) average FROM trips)

SELECT pickup_datetime, trips.trip_distance > avg_distance.average longer_than_average

FROM trips CROSS JOIN avg_distance;