Update and Insert Filters

Each WHEN MATCHED and WHEN NOT MATCHED clause in a MERGE statement can optionally specify an update filter and insert filter, respectively:

WHEN MATCHED AND update-filter THEN UPDATE …

WHEN NOT MATCHED AND insert-filter THEN INSERT …

Vertica also supports Oracle syntax for specifying update and insert filters:

WHEN MATCHED THEN UPDATE SET column-updates WHERE update-filter

WHEN NOT MATCHED THEN INSERT column-values WHERE insert-filter

Each filter can specify multiple conditions. Vertica handles the filters as follows:

• An update filter is applied to the set of matching rows in the target table that are returned by the MERGE join. For each row where the update filter evaluates to true, Vertica updates the specified columns.
• An insert filter is applied to the set of source table rows that are excluded from the MERGE join. For each row where the insert filter evaluates to true, Vertica adds a new row to the target table with the specified values.

For example, given the following data in tables t11 and t22:

=> SELECT * from t11 ORDER BY pk;
 pk | col1 | col2 | SKIP_ME_FLAG
----+------+------+--------------
  1 |    2 |    3 | t
  2 |    3 |    4 | t
  3 |    4 |    5 | f
  4 |      |    6 | f
  5 |    6 |    7 | t
  6 |      |    8 | f
  7 |    8 |      | t
(7 rows)

=> SELECT * FROM t22 ORDER BY pk;
 pk | col1 | col2
----+------+------
  1 |    2 |    4
  2 |    4 |    8
  3 |    6 |
  4 |    8 |   16
(4 rows)

You can merge data from table t11 into table t22 with the following MERGE statement, which includes update and insert filters:

=> MERGE INTO t22 USING t11 ON ( t11.pk=t22.pk )
   WHEN MATCHED 
       AND t11.SKIP_ME_FLAG=FALSE AND (
         COALESCE (t22.col1<>t11.col1, (t22.col1 is null)<>(t11.col1 is null))
       ) 
   THEN UPDATE SET col1=t11.col1, col2=t11.col2
   WHEN NOT MATCHED
      AND t11.SKIP_ME_FLAG=FALSE 
   THEN INSERT (pk, col1, col2) VALUES (t11.pk, t11.col1, t11.col2);
 OUTPUT
--------
      3
(1 row)

=> SELECT * FROM t22 ORDER BY pk;
 pk | col1 | col2
----+------+------
  1 |    2 |    4
  2 |    4 |    8
  3 |    4 |    5
  4 |      |    6
  6 |      |    8
(5 rows)

Vertica uses the update and insert filters as follows:

• Evaluates all matching rows against the update filter conditions. Vertica updates each row where the following two conditions both evaluate to true:
  • Source column t11.SKIP_ME_FLAG is set to false.
  • The COALESCE function evaluates to true.
• Evaluates all non-matching rows in the source table against the insert filter. For each row where column t11.SKIP_ME_FLAG is set to false, Vertica inserts a new row in the target table.