How Can I Reset a Postgres Primary Key Sequence Out of Sync with Table Rows?

Resolving PostgreSQL Primary Key Sequence Discrepancies

A primary key sequence misaligned with your table's rows can cause frustrating duplicate key errors. This often happens during data imports or restores where sequence integrity isn't preserved. Here's how to fix it:

1. Find the Highest ID:

Use the MAX() function to identify the largest ID in your table:

<code class="language-sql">SELECT MAX(id) FROM your_table;</code>

2. Get the Sequence's Next Value:

This query shows the sequence's next generated value:

<code class="language-sql">SELECT nextval('your_table_id_seq');</code>

3. Reset the Sequence (If Needed):

If the sequence's next value is smaller than the table's maximum ID, reset the sequence within a transaction to prevent concurrent inserts:

<code class="language-sql">BEGIN;
LOCK TABLE your_table IN EXCLUSIVE MODE;
SELECT setval('your_table_id_seq', (SELECT GREATEST(MAX(your_id), nextval('your_table_id_seq') - 1) FROM your_table));
COMMIT;</code>

Source: Adapted from a Ruby Forum discussion.

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