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WITH 语句 #

Batch Streaming

WITH provides a way to write auxiliary statements for use in a larger query. These statements, which are often referred to as Common Table Expression (CTE), can be thought of as defining temporary views that exist just for one query.

The syntax of WITH statement is:

WITH <with_item_definition> [ , ... ]
SELECT ... FROM ...;

<with_item_defintion>:
    with_item_name (column_name[, ...n]) AS ( <select_query> )

The following example defines a common table expression orders_with_total and use it in a GROUP BY query.

WITH orders_with_total AS (
    SELECT order_id, price + tax AS total
    FROM Orders
)
SELECT order_id, SUM(total)
FROM orders_with_total
GROUP BY order_id;