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64 lines
1.8 KiB
Plaintext
64 lines
1.8 KiB
Plaintext
-----------------
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MERGE statement
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-----------------
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Function:
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Read data from the source and INSERT or UPDATE in the target table depending on a
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condition.
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Author:
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Adriano dos Santos Fernandes <adrianosf@uol.com.br>
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Format:
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<merge statement> ::=
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MERGE
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INTO <table or view> [ [AS] <correlation name> ]
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USING <table or view or derived table> [ [AS] <correlation name> ]
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ON <condition>
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<merge when>...
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<returning clause>
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<merge when> ::=
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<merge when matched> |
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<merge when not matched>
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<merge when matched> ::=
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WHEN MATCHED [ AND <condition> ] THEN
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{ UPDATE SET <assignment list> | DELETE }
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<merge when not matched> ::=
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WHEN NOT MATCHED [ AND <condition> ] THEN
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INSERT [ <left paren> <column list> <right paren> ]
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VALUES <left paren> <value list> <right paren>
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Syntax rules:
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1. At least one of <merge when matched> or <merge when not matched> should be specified.
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Scope:
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DSQL, PSQL
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Examples:
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1.
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MERGE
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INTO customers c
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USING (SELECT * FROM customers_delta WHERE id > 10) cd
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ON (c.id = cd.id)
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WHEN MATCHED THEN
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UPDATE SET
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name = cd.name
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WHEN NOT MATCHED THEN
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INSERT (id, name)
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VALUES (cd.id, cd.name)
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Notes:
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A right join is made between INTO and USING tables using the condition.
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UPDATE is called when a record exist in the left table (INTO), otherwise
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INSERT is called.
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As soon it's decided if the source matched or not a record in the target, the set of the
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corresponding (WHEN MATCHED / WHEN NOT MATCHED) statements is evaluated in the order specified,
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to check their optional conditions. The first statement which has its condition evaluated to true
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is the one which will be executed, and the subsequent ones will be ignored.
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If no record is returned in the join, INSERT is not called.
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