ignore_row_on_dupkey_index tips

Oracle Database Tips by Donald BurlesonJanuary 1, 2015

Oracle 11g now has a feature to silently allow insert SQL to accept duplicates with the ignore_row_on_dupkey_index hint. When ignore_row_on_dupkey_index hint is used in a SQL insert on a table with a unique key index, all duplicates will be silently ignored, rather than causing the traditional error, ORA-00001 unique constraint violated.

The Oracle docs note that the ignore_row_on_dupkey_index are unlike any other hints because they have an effect on the semantics of the SQL statement, actually changing the functionality of the DML statament:

The change_dupkey_error_index, ignore_row_on_dupkey_index, and retry_on_row_change hints are unlike other hints in that they have a semantic effect.

The general philosophy explained in "Hints" does not apply for these three hints.

The ignore_row_on_dupkey_index hint is also unique because unlike a regular hint (hints are embedded inside comments), you will get an error. In traditional SQL hints, hints with syntax, semantic or resource errors will cause the hint to be ignored.

However, this hint will cause an ORA-38912 error if you don't pass the correct arguments. Note that the ignore_row_on_dupkey_index hint requires two arguments, the table name and index name. If the index name is omitted, the ORA-38912 error is thrown:

insert /*+ ignore_row_on_dupkey_index(unique_cust) */
into
unique_cust
(select * from non_unique_cust);

ORA-38912: An index must be specified in the index hint

Cause: Index specification was missing in an ignore_row_on_dupkey_index or change_dupkey_error_index hint.

Action: In the hint, specify a unique index that exists on the table.

Functionally, the ignore_row_on_dupkey_index hint is somewhat similar to the SQL merge statement because it ignores duplicates on insert.

Examples of using the ignore_row_on_dupkey_index hint

Here is an example of using this hint to load a unique table from a non-unique table, while preventing aborts due to duplicate values:

insert /*+ ignore_row_on_dupkey_index(unique_cust, unique_cust_pk_idx) */
into
unique_cust
(select * from non_unique_cust);

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