Fixing Sequences

Updating sequence values from table

Administrative Snippets

Fixing Sequences

Works with PostgreSQL

8.4+

Written in

SQL

Depends on

Nothing

A common problem when copying or recreating a database is that database sequences are not updated just by inserting records in the table that sequence is used in. If you want to make your sequences all start just after whatever values are already there, it's possible to do that for most common configurations like this:

SELECT 
    'SELECT SETVAL(' ||
       quote_literal(quote_ident(sequence_namespace.nspname) || '.' || quote_ident(class_sequence.relname)) ||
       ', COALESCE(MAX(' ||quote_ident(pg_attribute.attname)|| '), 1) ) FROM ' ||
       quote_ident(table_namespace.nspname)|| '.'||quote_ident(class_table.relname)|| ';'
FROM pg_depend 
    INNER JOIN pg_class AS class_sequence
        ON class_sequence.oid = pg_depend.objid 
            AND class_sequence.relkind = 'S'
    INNER JOIN pg_class AS class_table
        ON class_table.oid = pg_depend.refobjid
    INNER JOIN pg_attribute 
        ON pg_attribute.attrelid = class_table.oid
            AND pg_depend.refobjsubid = pg_attribute.attnum
    INNER JOIN pg_namespace as table_namespace
        ON table_namespace.oid = class_table.relnamespace
    INNER JOIN pg_namespace AS sequence_namespace
        ON sequence_namespace.oid = class_sequence.relnamespace
ORDER BY sequence_namespace.nspname, class_sequence.relname;

Usage would typically work like this:

• Save this to a file, say 'reset.sql'
• Run the file and save its output in a way that doesn't include the usual headers, then run that output. Example:

psql -Atq -f reset.sql -o temp
psql -f temp
rm temp

There are a few limitations to this snippet of code you need to be aware of:

• It only works on sequences that are owned by a table. If your sequences are not owned, run the following script first:

Fixing sequence ownership

This script changes sequences with OWNED BY to the table and column they're referenced from. NB! Sequences that are referenced by multiple tables or columns are ignored.

(Parts of query shamelessly stolen from OmniTI's Tasty Treats repository by Robert Treat)

select 'ALTER SEQUENCE '|| quote_ident(min(schema_name)) ||'.'|| quote_ident(min(seq_name))
       ||' OWNED BY '|| quote_ident(min(table_name)) ||'.'|| quote_ident(min(column_name)) ||';'
from (
    select 
        n.nspname as schema_name,
        c.relname as table_name,
        a.attname as column_name,
        substring(d.adsrc from E'^nextval\\(''([^'']*)''(?:::text|::regclass)?\\)') as seq_name 
    from pg_class c 
    join pg_attribute a on (c.oid=a.attrelid) 
    join pg_attrdef d on (a.attrelid=d.adrelid and a.attnum=d.adnum) 
    join pg_namespace n on (c.relnamespace=n.oid)
    where has_schema_privilege(n.oid,'USAGE')
      and n.nspname not like 'pg!_%' escape '!'
      and has_table_privilege(c.oid,'SELECT')
      and (not a.attisdropped)
      and d.adsrc ~ '^nextval'
) seq
group by seq_name having count(*)=1;

---

This snippet finds orphaned sequences that aren't owned by any column. It can be helpful to run this, to double-check that the above query did its job right.

select ns.nspname as schema_name, seq.relname as seq_name
from pg_class as seq
join pg_namespace ns on (seq.relnamespace=ns.oid)
where seq.relkind = 'S'
  and not exists (select * from pg_depend where objid=seq.oid and deptype='a' and classid = 'pg_class'::regclass)
order by seq.relname;