Re: Duplicate key error

On 11/11/24 07:40, yudhi s wrote:

> We have a merge query as below for a partition table which is range
> partitioned on a truncated date column 'part_date'. And the only
> unique key in this table is a composite primary key on (id,
> part_date). And this merge queries ON condition is based on one of the
> columns i.e ID which is the leading column of the PK.So it means it
> will ensure no duplication happens for ID values, but still we are
> seeing "duplicate key" error. So what is the possible reason here or
> are we encountering any buggy behaviour here?
>
> WITH source_data (col1, col2, col3.....col29) AS (VALUES ($1,
> $2::date, $3::timestamptz, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13,
> $14, $15, $16, $17, $18, $19, $20, $21, $22, $23, $24, $25, $26,
> $27::timestamptz, $28, $29::timestamptz)) MERGE INTO cpod.TAB1 AS
> target USING source_data AS source ON target.ID = source.ID WHEN
> MATCHED THEN UPDATE SET ....) WHEN NOT MATCHED THEN INSERT (...)
> VALUES (....);
>
> Error:
> ERROR: duplicate key value violates unique constraint "TAB1_pkey"
> Detail: Key (ID, part_date)=(XXXXXXXXX, 2024-11-04) already exists.

You have to use the whole composite unique key (including part_date)
when matching against source_data .

If you had uniqueness on "ID" and then added "part_name" to the key,
you'd still had uniqueness.

BUT, reversely, if you have uniqueness on the pair (ID, part_date) there
is no guaranteed uniqueness on ID alone, hence your ERROR.

>
> Regards
> Yudhi
>