WITH keyword

Supports Common Table Expressions (CTEs), e.i., naming one or several sub-queries to be used with a SELECT, INSERT, or UPDATE query.

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

Syntax

Where:

• alias is the name given to the sub-query for ease of reusing
• subQuery is a SQL query (e.g SELECT * FROM table)

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;

Update with a sub-query

WITH up AS (
    SELECT symbol, spread, ts
    FROM temp_spreads
    WHERE timestamp between '2022-01-02' and '2022-01-03'
)
UPDATE spreads s
SET spread = up.spread
FROM up
WHERE up.ts = s.ts AND s.symbol = up.symbol;

Insert with a sub-query

WITH up AS (
    SELECT symbol, spread, ts
    FROM temp_spreads
    WHERE timestamp between '2022-01-02' and '2022-01-03'
)
INSERT INTO spreads
SELECT * FROM up;