### 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>
125 lines
2.8 KiB
Markdown
125 lines
2.8 KiB
Markdown
---
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layout: global
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title: Common Table Expression (CTE)
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displayTitle: Common Table Expression (CTE)
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license: |
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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---
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### Description
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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.
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### Syntax
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```sql
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WITH common_table_expression [ , ... ]
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```
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While `common_table_expression` is defined as
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```sql
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expression_name [ ( column_name [ , ... ] ) ] [ AS ] ( query )
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```
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### Parameters
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* **expression_name**
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Specifies a name for the common table expression.
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* **query**
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A [SELECT statement](sql-ref-syntax-qry-select.html).
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### Examples
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```sql
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-- CTE with multiple column aliases
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WITH t(x, y) AS (SELECT 1, 2)
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SELECT * FROM t WHERE x = 1 AND y = 2;
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+---+---+
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| x| y|
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+---+---+
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| 1| 2|
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+---+---+
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-- CTE in CTE definition
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WITH t AS (
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WITH t2 AS (SELECT 1)
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SELECT * FROM t2
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)
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SELECT * FROM t;
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+---+
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| 1|
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+---+
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| 1|
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+---+
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-- CTE in subquery
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SELECT max(c) FROM (
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WITH t(c) AS (SELECT 1)
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SELECT * FROM t
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);
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+------+
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|max(c)|
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+------+
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| 1|
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+------+
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-- CTE in subquery expression
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SELECT (
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WITH t AS (SELECT 1)
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SELECT * FROM t
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);
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+----------------+
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|scalarsubquery()|
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+----------------+
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| 1|
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+----------------+
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-- CTE in CREATE VIEW statement
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CREATE VIEW v AS
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WITH t(a, b, c, d) AS (SELECT 1, 2, 3, 4)
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SELECT * FROM t;
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SELECT * FROM v;
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+---+---+---+---+
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| a| b| c| d|
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+---+---+---+---+
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| 1| 2| 3| 4|
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+---+---+---+---+
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-- If name conflict is detected in nested CTE, then AnalysisException is thrown by default.
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-- SET spark.sql.legacy.ctePrecedencePolicy = CORRECTED (which is recommended),
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-- inner CTE definitions take precedence over outer definitions.
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SET spark.sql.legacy.ctePrecedencePolicy = CORRECTED;
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WITH
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t AS (SELECT 1),
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t2 AS (
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WITH t AS (SELECT 2)
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SELECT * FROM t
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)
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SELECT * FROM t2;
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+---+
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| 2|
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+---+
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| 2|
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+---+
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```
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### Related Statements
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* [SELECT](sql-ref-syntax-qry-select.html)
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