Details
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Task
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Status: In Review (View Workflow)
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Critical
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Resolution: Unresolved
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None
Description
In MariaDB for table value constructors, the column names are taken from the value of the first set of results
MariaDB [test]> values (3,4),(5,6);
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+---+---+
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| 3 | 4 |
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+---+---+
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| 3 | 4 |
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| 5 | 6 |
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+---+---+
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2 rows in set (0.002 sec)
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There is no mechanism to assign them names. The SQL standard tells us that the column name(s) for a table value expression is "implementation dependent".
PostgreSQL can (re)assign column names in the derived table name syntax element.
rex=# select * from (values (3,4),(5,6)) as foo(Col1, Col2);
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col1 | col2
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------+------
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3 | 4
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5 | 6
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(2 rows)
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rex=# select * from (select concat(col1, col2) from (values (3,4)) as foo(col1,col2)) as foo2 (a);
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a
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----
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34
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(1 row)
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This is similar to the syntax used in the specification of a CTE, i.e.
MariaDB [test]> WITH cte(a,b) as (values (3,4),(5,6) ) select * from cte ;
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+---+---+
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| a | b |
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+---+---+
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| 3 | 4 |
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| 5 | 6 |
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+---+---+
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2 rows in set (0.005 sec)
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The SQL (2016) Foundation document, (starting at page 406) describes this syntax for the <table primary> syntax element.
Note the option of this being <derived table> <correlation or recognition>
where <derived table> translates into '(' <query expression> ')'.
<table primary> ::=
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<table or query name>
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[ <query system time period specification> ]
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[ <correlation or recognition> ]
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| <derived table> <correlation or recognition>
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| <lateral derived table> <correlation or recognition>
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| <collection derived table> <correlation or recognition>
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| <table function derived table> <correlation or recognition>
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| <PTF derived table> [ <correlation or recognition> ]
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| <only spec> [ <correlation or recognition> ]
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| <data change delta table> [ <correlation or recognition> ]
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| <JSON table> <correlation or recognition>
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| <JSON table primitive> <correlation name>
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| <parenthesized joined table>
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<correlation or recognition> ::=
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[ AS ] <correlation name>
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[ <parenthesized derived column list> ]
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<parenthesized derived column list> ::=
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<left paren> <derived column list> <right paren>
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<derived column list> ::=
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<column name list>
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<column name list> ::=
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<column name> [ { <comma> <column name> }... ]
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The MDEV covers the implementation of this for MariaDB.
Attachments
Issue Links
- relates to
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MDEV-34506 2nd execution name resolution problem with pushdown into unions
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- In Review
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