a75dc80a76
### What changes were proposed in this pull request? Remove the unneeded embedded inline HTML markup by using the basic markdown syntax. Please see #28414 ### Why are the changes needed? Make the doc cleaner and easily editable by MD editors. ### Does this PR introduce _any_ user-facing change? No ### How was this patch tested? Manually build and check Closes #28451 from huaxingao/html_cleanup. Authored-by: Huaxin Gao <huaxing@us.ibm.com> Signed-off-by: Sean Owen <srowen@gmail.com>
2.8 KiB
2.8 KiB
layout | title | displayTitle | license |
---|---|---|---|
global | 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
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|
+---+---+---+---+
-- If name conflict is detected in nested CTE, then AnalysisException is thrown by default.
-- SET spark.sql.legacy.ctePrecedencePolicy = CORRECTED (which is recommended),
-- inner CTE definitions take precedence over outer definitions.
SET spark.sql.legacy.ctePrecedencePolicy = CORRECTED;
WITH
t AS (SELECT 1),
t2 AS (
WITH t AS (SELECT 2)
SELECT * FROM t
)
SELECT * FROM t2;
+---+
| 2|
+---+
| 2|
+---+