WITH Clause - Common table expressions in Bigquery
You can easily create CTEs (temp tables that live for the session duration) in Bigquery by using query names. The query names in a WITH clause (see WITH Clause) act like names of temporary tables that you can reference anywhere in the FROM clause. In the example below, subQ1 and subQ2 are with_query_names
subQ1 AS (SELECT * FROM Roster WHERE SchoolID = 52),
subQ2 AS (SELECT SchoolID FROM subQ1)
SELECT DISTINCT * FROM subQ2;
NOTE: The WITH clause hides any permanent tables with the same name for the duration of the query, unless you qualify the table name, e.g. dataset.Roster or project.dataset.Roster
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