List all sequences in a Postgres db 8.1 with SQL

Question

I\'m converting a db from postgres to mysql.

Since i cannot find a tool that does the trick itself, i\'m going to convert all postgres sequences to autoincrement id

Answer 1

I know this post is pretty old, but I found the solution by CMS to be very useful as I was looking for an automated way to link a sequence to the table AND column, and wanted to share. The use of pg_depend catalog table was the key. I expanded what was done to:

WITH fq_objects AS (SELECT c.oid,n.nspname || '.' ||c.relname AS fqname ,
                           c.relkind, c.relname AS relation
                    FROM pg_class c JOIN pg_namespace n ON n.oid = c.relnamespace ),

     sequences AS (SELECT oid,fqname FROM fq_objects WHERE relkind = 'S'),
     tables    AS (SELECT oid, fqname FROM fq_objects WHERE relkind = 'r' )
SELECT
       s.fqname AS sequence,
       '->' as depends,
       t.fqname AS table,
       a.attname AS column
FROM
     pg_depend d JOIN sequences s ON s.oid = d.objid
                 JOIN tables t ON t.oid = d.refobjid
                 JOIN pg_attribute a ON a.attrelid = d.refobjid and a.attnum = d.refobjsubid
WHERE
     d.deptype = 'a' ;

This version adds column to the list of fields returned. With both the table name and the column name in hand, a call to pg_set_serial_sequence makes it easy to ensure that all sequences in the database are set correctly. For example:

CREATE OR REPLACE FUNCTION public.reset_sequence(tablename text, columnname text)
 RETURNS void
 LANGUAGE plpgsql
AS $function$
DECLARE
    _sql VARCHAR := '';
BEGIN
    _sql := $$SELECT setval( pg_get_serial_sequence('$$ || tablename || $$', '$$ || columnname || $$'), (SELECT COALESCE(MAX($$ || columnname || $$),1) FROM $$ || tablename || $$), true)$$;
    EXECUTE _sql;
END;
$function$;

Hope this helps someone with resetting sequences!

Answer 2

Assuming exec() function declared in this post https://stackoverflow.com/a/46721603/653539 , sequences together with their last values can be fetched using single query:

select s.sequence_schema, s.sequence_name,
  (select * from exec('select last_value from ' || s.sequence_schema || '.' || s.sequence_name) as e(lv bigint)) last_value
from information_schema.sequences s

Answer 3

This function shows the last_value of each sequence.

It outputs a 2 columns table that says the sequence name plus it's last generated value.

drop function if exists public.show_sequence_stats();
CREATE OR REPLACE FUNCTION public.show_sequence_stats()
    RETURNS TABLE(tablename text, last_value bigint) 
    LANGUAGE 'plpgsql'
    COST 100
    VOLATILE 
    ROWS 1000
AS $BODY$
declare r refcursor; rec record; dynamic_query varchar;
        BEGIN
            dynamic_query='select tablename,last_value from (';
            open r for execute 'select nspname,relname from pg_class c join pg_namespace n on c.relnamespace=n.oid where relkind = ''S'' order by nspname'; 
            fetch next from r into rec;
            while found 
            loop
                dynamic_query=dynamic_query || 'select '''|| rec.nspname || '.' || rec.relname ||''' "tablename",last_value from ' || rec.nspname || '.' || rec.relname || ' union all ';
                fetch next from r into rec; 
            end loop;
            close r; 
            dynamic_query=rtrim(dynamic_query,'union all') || ') x order by last_value desc;';
            return query execute dynamic_query;
        END;
$BODY$;

select * from show_sequence_stats();

Answer 4

Partially tested but looks mostly complete.

select *
  from (select n.nspname,c.relname,
               (select substring(pg_catalog.pg_get_expr(d.adbin, d.adrelid) for 128)
                  from pg_catalog.pg_attrdef d
                 where d.adrelid=a.attrelid
                   and d.adnum=a.attnum
                   and a.atthasdef) as def
          from pg_class c, pg_attribute a, pg_namespace n
         where c.relkind='r'
           and c.oid=a.attrelid
           and n.oid=c.relnamespace
           and a.atthasdef
           and a.atttypid=20) x
 where x.def ~ '^nextval'
 order by nspname,relname;

Credit where credit is due... it's partly reverse engineered from the SQL logged from a \d on a known table that had a sequence. I'm sure it could be cleaner too, but hey, performance wasn't a concern.

Answer 5

The relationship between automatically generated sequences ( such as those created for SERIAL columns ) and the parent table is modelled by the sequence owner attribute.

You can modify this relationship using the OWNED BY clause of the ALTER SEQUENCE commmand

e.g. ALTER SEQUENCE foo_id OWNED by foo_schema.foo_table

to set it to be linked to the table foo_table

or ALTER SEQUENCE foo_id OWNED by NONE

to break the connection between the sequence and any table

The information about this relationship is stored in the pg_depend catalogue table.

the joining relationship is the link between pg_depend.objid -> pg_class.oid WHERE relkind = 'S' - which links the sequence to the join record and then pg_depend.refobjid -> pg_class.oid WHERE relkind = 'r' , which links the join record to the owning relation ( table )

This query returns all the sequence -> table dependencies in a database. The where clause filters it to only include auto generated relationships, which restricts it to only display sequences created by SERIAL typed columns.

WITH fq_objects AS (SELECT c.oid,n.nspname || '.' ||c.relname AS fqname , 
                           c.relkind, c.relname AS relation 
                    FROM pg_class c JOIN pg_namespace n ON n.oid = c.relnamespace ),

     sequences AS (SELECT oid,fqname FROM fq_objects WHERE relkind = 'S'),  
     tables    AS (SELECT oid, fqname FROM fq_objects WHERE relkind = 'r' )  
SELECT
       s.fqname AS sequence, 
       '->' as depends, 
       t.fqname AS table 
FROM 
     pg_depend d JOIN sequences s ON s.oid = d.objid  
                 JOIN tables t ON t.oid = d.refobjid  
WHERE 
     d.deptype = 'a' ;

Answer 6

sequence info : max value

SELECT * FROM information_schema.sequences;

sequence info : last value

SELECT * FROM <sequence_name>