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Common Table Expression (CTE)
Common Table Expression (CTE)
Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Description

A common table expression (CTE) defines a temporary result set that a user can reference possibly multiple times within the scope of a SQL statement. A CTE is used mainly in a SELECT statement.

Syntax

WITH common_table_expression [ , ... ]

While common_table_expression is defined as

expression_name [ ( column_name [ , ... ] ) ] [ AS ] ( query )

Parameters

  • expression_name

    Specifies a name for the common table expression.

  • query

    A SELECT statement.

Examples

-- CTE with multiple column aliases
WITH t(x, y) AS (SELECT 1, 2)
SELECT * FROM t WHERE x = 1 AND y = 2;
+---+---+
|  x|  y|
+---+---+
|  1|  2|
+---+---+

-- CTE in CTE definition
WITH t AS (
    WITH t2 AS (SELECT 1)
    SELECT * FROM t2
)
SELECT * FROM t;
+---+
|  1|
+---+
|  1|
+---+

-- CTE in subquery
SELECT max(c) FROM (
    WITH t(c) AS (SELECT 1)
    SELECT * FROM t
);
+------+
|max(c)|
+------+
|     1|
+------+

-- CTE in subquery expression
SELECT (
    WITH t AS (SELECT 1)
    SELECT * FROM t
);
+----------------+
|scalarsubquery()|
+----------------+
|               1|
+----------------+

-- CTE in CREATE VIEW statement
CREATE VIEW v AS
    WITH t(a, b, c, d) AS (SELECT 1, 2, 3, 4)
    SELECT * FROM t;
SELECT * FROM v;
+---+---+---+---+
|  a|  b|  c|  d|
+---+---+---+---+
|  1|  2|  3|  4|
+---+---+---+---+

WITH
    t AS (SELECT 1),
    t2 AS (
        WITH t AS (SELECT 2)
        SELECT * FROM t
    )
SELECT * FROM t2;
+---+
|  2|
+---+
|  2|
+---+

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