MERGE

Примечание

Ниже приведена оригинальная документация Trino. Скоро мы ее переведем на русский язык и дополним полезными примерами.

Синтаксис

MERGE INTO target_table [ [ AS ]  target_alias ]
USING { source_table | query } [ [ AS ] source_alias ]
ON search_condition
when_clause [...]

where when_clause is one of

WHEN MATCHED [ AND condition ]
    THEN DELETE

WHEN MATCHED [ AND condition ]
    THEN UPDATE SET ( column = expression [, ...] )

WHEN NOT MATCHED [ AND condition ]
    THEN INSERT [ column_list ] VALUES (expression, ...)

Описание

Conditionally update and/or delete rows of a table and/or insert new rows into a table.

MERGE supports an arbitrary number of WHEN clauses with different MATCHED conditions, executing the DELETE, UPDATE or INSERT operation in the first WHEN clause selected by the MATCHED state and the match condition.

For each source row, the WHEN clauses are processed in order. Only the first first matching WHEN clause is executed and subsequent clauses are ignored. A MERGE_TARGET_ROW_MULTIPLE_MATCHES exception is raised when a single target table row matches more than one source row.

If a source row is not matched by any WHEN clause and there is no WHEN NOT MATCHED clause, the source row is ignored.

In WHEN clauses with UPDATE operations, the column value expressions can depend on any field of the target or the source. In the NOT MATCHED case, the INSERT expressions can depend on any field of the source.

Примеры

Delete all customers mentioned in the source table:

MERGE INTO accounts t USING monthly_accounts_update s
    ON t.customer = s.customer
    WHEN MATCHED
        THEN DELETE

For matching customer rows, increment the purchases, and if there is no match, insert the row from the source table:

MERGE INTO accounts t USING monthly_accounts_update s
    ON (t.customer = s.customer)
    WHEN MATCHED
        THEN UPDATE SET purchases = s.purchases + t.purchases
    WHEN NOT MATCHED
        THEN INSERT (customer, purchases, address)
              VALUES(s.customer, s.purchases, s.address)

MERGE into the target table from the source table, deleting any matching target row for which the source address is Centreville. For all other matching rows, add the source purchases and set the address to the source address, if there is no match in the target table, insert the source table row:

MERGE INTO accounts t USING monthly_accounts_update s
    ON (t.customer = s.customer)
    WHEN MATCHED AND s.address = 'Centreville'
        THEN DELETE
    WHEN MATCHED
        THEN UPDATE
            SET purchases = s.purchases + t.purchases, address = s.address
    WHEN NOT MATCHED
        THEN INSERT (customer, purchases, address)
              VALUES(s.customer, s.purchases, s.address)

Limitations

Any connector can be used as a source table for a MERGE statement. Only connectors which support the MERGE statement can be the target of a merge operation. See the connector documentation for more information.