[SPARK-31428][SQL][DOCS] Document Common Table Expression in SQL Reference
### What changes were proposed in this pull request? Document Common Table Expression in SQL Reference ### Why are the changes needed? Make SQL Reference complete ### Does this PR introduce any user-facing change? Yes <img width="1050" alt="Screen Shot 2020-04-13 at 12 06 35 AM" src="https://user-images.githubusercontent.com/13592258/79100257-f61def00-7d1a-11ea-8402-17017059232e.png"> <img width="1050" alt="Screen Shot 2020-04-13 at 12 07 09 AM" src="https://user-images.githubusercontent.com/13592258/79100260-f7e7b280-7d1a-11ea-9408-058c0851f0b6.png"> <img width="1050" alt="Screen Shot 2020-04-13 at 12 07 35 AM" src="https://user-images.githubusercontent.com/13592258/79100262-fa4a0c80-7d1a-11ea-8862-eb1d8960296b.png"> Also link to Select page <img width="1045" alt="Screen Shot 2020-04-12 at 4 14 30 PM" src="https://user-images.githubusercontent.com/13592258/79082246-217fea00-7cd9-11ea-8d96-1a69769d1e19.png"> ### How was this patch tested? Manually build and check Closes #28196 from huaxingao/cte. Authored-by: Huaxin Gao <huaxing@us.ibm.com> Signed-off-by: Takeshi Yamamuro <yamamuro@apache.org>
This commit is contained in:
Huaxin Gao
Takeshi Yamamuro
parent
0d4e4df061
commit
92c1b24617
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@ -166,6 +166,8 @@
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url: sql-ref-syntax-qry-select-tvf.html
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- text: Inline Table
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url: sql-ref-syntax-qry-select-inline-table.html
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- text: Common Table Expression
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url: sql-ref-syntax-qry-select-cte.html
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- text: EXPLAIN
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url: sql-ref-syntax-qry-explain.html
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- text: Auxiliary Statements
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@ -19,4 +19,111 @@ license: |
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limitations under the License.
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---
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**This page is under construction**
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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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{% highlight sql %}
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WITH common_table_expression [ , ... ]
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{% endhighlight %}
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While `common_table_expression` is defined as
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{% highlight sql %}
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expression_name [ ( column_name [ , ... ] ) ] [ AS ] ( [ common_table_expression ] query )
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{% endhighlight %}
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### Parameters
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<dl>
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<dt><code><em>expression_name</em></code></dt>
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<dd>
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Specifies a name for the common table expression.
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</dd>
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</dl>
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<dl>
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<dt><code><em>query</em></code></dt>
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<dd>
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A <a href="sql-ref-syntax-qry-select.html">SELECT</a> statement.
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</dd>
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</dl>
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### Examples
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{% highlight 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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{% endhighlight %}
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### Related Statements
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* [SELECT](sql-ref-syntax-qry-select.html)
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@ -53,7 +53,7 @@ SELECT [ hints , ... ] [ ALL | DISTINCT ] { named_expression [ , ... ] }
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<dl>
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<dt><code><em>with_query</em></code></dt>
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<dd>
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Specifies the common table expressions (CTEs) before the main query block.
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Specifies the <a href="sql-ref-syntax-qry-select-cte.html">common table expressions (CTEs)</a> before the main query block.
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These table expressions are allowed to be referenced later in the FROM clause. This is useful to abstract
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out repeated subquery blocks in the FROM clause and improves readability of the query.
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</dd>
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@ -159,3 +159,4 @@ SELECT [ hints , ... ] [ ALL | DISTINCT ] { named_expression [ , ... ] }
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* [TABLESAMPLE](sql-ref-syntax-qry-sampling.html)
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* [JOIN](sql-ref-syntax-qry-select-join.html)
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* [SET Operators](sql-ref-syntax-qry-select-setops.html)
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* [Common Table Expression](sql-ref-syntax-qry-select-cte.html)
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