Advertisement
Advertisement


How do you find the row count for all your tables in Postgres


Question

I'm looking for a way to find the row count for all my tables in Postgres. I know I can do this one table at a time with:

SELECT count(*) FROM table_name;

but I'd like to see the row count for all the tables and then order by that to get an idea of how big all my tables are.

2018/03/07
1
402
3/7/2018 10:48:07 AM

Accepted Answer

There's three ways to get this sort of count, each with their own tradeoffs.

If you want a true count, you have to execute the SELECT statement like the one you used against each table. This is because PostgreSQL keeps row visibility information in the row itself, not anywhere else, so any accurate count can only be relative to some transaction. You're getting a count of what that transaction sees at the point in time when it executes. You could automate this to run against every table in the database, but you probably don't need that level of accuracy or want to wait that long.

The second approach notes that the statistics collector tracks roughly how many rows are "live" (not deleted or obsoleted by later updates) at any time. This value can be off by a bit under heavy activity, but is generally a good estimate:

SELECT schemaname,relname,n_live_tup 
  FROM pg_stat_user_tables 
  ORDER BY n_live_tup DESC;

That can also show you how many rows are dead, which is itself an interesting number to monitor.

The third way is to note that the system ANALYZE command, which is executed by the autovacuum process regularly as of PostgreSQL 8.3 to update table statistics, also computes a row estimate. You can grab that one like this:

SELECT 
  nspname AS schemaname,relname,reltuples
FROM pg_class C
LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
WHERE 
  nspname NOT IN ('pg_catalog', 'information_schema') AND
  relkind='r' 
ORDER BY reltuples DESC;

Which of these queries is better to use is hard to say. Normally I make that decision based on whether there's more useful information I also want to use inside of pg_class or inside of pg_stat_user_tables. For basic counting purposes just to see how big things are in general, either should be accurate enough.

2010/04/10
600
4/10/2010 12:26:26 AM

Here is a solution that does not require functions to get an accurate count for each table:

select table_schema, 
       table_name, 
       (xpath('/row/cnt/text()', xml_count))[1]::text::int as row_count
from (
  select table_name, table_schema, 
         query_to_xml(format('select count(*) as cnt from %I.%I', table_schema, table_name), false, true, '') as xml_count
  from information_schema.tables
  where table_schema = 'public' --<< change here for the schema you want
) t

query_to_xml will run the passed SQL query and return an XML with the result (the row count for that table). The outer xpath() will then extract the count information from that xml and convert it to a number

The derived table is not really necessary, but makes the xpath() a bit easier to understand - otherwise the whole query_to_xml() would need to be passed to the xpath() function.


To get estimates, see Greg Smith's answer.

To get exact counts, the other answers so far are plagued with some issues, some of them serious (see below). Here's a version that's hopefully better:

CREATE FUNCTION rowcount_all(schema_name text default 'public')
  RETURNS table(table_name text, cnt bigint) as
$$
declare
 table_name text;
begin
  for table_name in SELECT c.relname FROM pg_class c
    JOIN pg_namespace s ON (c.relnamespace=s.oid)
    WHERE c.relkind = 'r' AND s.nspname=schema_name
  LOOP
    RETURN QUERY EXECUTE format('select cast(%L as text),count(*) from %I.%I',
       table_name, schema_name, table_name);
  END LOOP;
end
$$ language plpgsql;

It takes a schema name as parameter, or public if no parameter is given.

To work with a specific list of schemas or a list coming from a query without modifying the function, it can be called from within a query like this:

WITH rc(schema_name,tbl) AS (
  select s.n,rowcount_all(s.n) from (values ('schema1'),('schema2')) as s(n)
)
SELECT schema_name,(tbl).* FROM rc;

This produces a 3-columns output with the schema, the table and the rows count.

Now here are some issues in the other answers that this function avoids:

  • Table and schema names shouldn't be injected into executable SQL without being quoted, either with quote_ident or with the more modern format() function with its %I format string. Otherwise some malicious person may name their table tablename;DROP TABLE other_table which is perfectly valid as a table name.

  • Even without the SQL injection and funny characters problems, table name may exist in variants differing by case. If a table is named ABCD and another one abcd, the SELECT count(*) FROM... must use a quoted name otherwise it will skip ABCD and count abcd twice. The %I of format does this automatically.

  • information_schema.tables lists custom composite types in addition to tables, even when table_type is 'BASE TABLE' (!). As a consequence, we can't iterate oninformation_schema.tables, otherwise we risk having select count(*) from name_of_composite_type and that would fail. OTOH pg_class where relkind='r' should always work fine.

  • The type of COUNT() is bigint, not int. Tables with more than 2.15 billion rows may exist (running a count(*) on them is a bad idea, though).

  • A permanent type need not to be created for a function to return a resultset with several columns. RETURNS TABLE(definition...) is a better alternative.

2017/05/23

If you don't mind potentially stale data, you can access the same statistics used by the query optimizer.

Something like:

SELECT relname, n_tup_ins - n_tup_del as rowcount FROM pg_stat_all_tables;
2010/04/07

The hacky, practical answer for people trying to evaluate which Heroku plan they need and can't wait for heroku's slow row counter to refresh:

Basically you want to run \dt in psql, copy the results to your favorite text editor (it will look like this:

 public | auth_group                     | table | axrsosvelhutvw
 public | auth_group_permissions         | table | axrsosvelhutvw
 public | auth_permission                | table | axrsosvelhutvw
 public | auth_user                      | table | axrsosvelhutvw
 public | auth_user_groups               | table | axrsosvelhutvw
 public | auth_user_user_permissions     | table | axrsosvelhutvw
 public | background_task                | table | axrsosvelhutvw
 public | django_admin_log               | table | axrsosvelhutvw
 public | django_content_type            | table | axrsosvelhutvw
 public | django_migrations              | table | axrsosvelhutvw
 public | django_session                 | table | axrsosvelhutvw
 public | exercises_assignment           | table | axrsosvelhutvw

), then run a regex search and replace like this:

^[^|]*\|\s+([^|]*?)\s+\| table \|.*$

to:

select '\1', count(*) from \1 union/g

which will yield you something very similar to this:

select 'auth_group', count(*) from auth_group union
select 'auth_group_permissions', count(*) from auth_group_permissions union
select 'auth_permission', count(*) from auth_permission union
select 'auth_user', count(*) from auth_user union
select 'auth_user_groups', count(*) from auth_user_groups union
select 'auth_user_user_permissions', count(*) from auth_user_user_permissions union
select 'background_task', count(*) from background_task union
select 'django_admin_log', count(*) from django_admin_log union
select 'django_content_type', count(*) from django_content_type union
select 'django_migrations', count(*) from django_migrations union
select 'django_session', count(*) from django_session
;

(You'll need to remove the last union and add the semicolon at the end manually)

Run it in psql and you're done.

            ?column?            | count
--------------------------------+-------
 auth_group_permissions         |     0
 auth_user_user_permissions     |     0
 django_session                 |  1306
 django_content_type            |    17
 auth_user_groups               |   162
 django_admin_log               |  9106
 django_migrations              |    19
[..]
2019/06/30

Not sure if an answer in bash is acceptable to you, but FWIW...

PGCOMMAND=" psql -h localhost -U fred -d mydb -At -c \"
            SELECT   table_name
            FROM     information_schema.tables
            WHERE    table_type='BASE TABLE'
            AND      table_schema='public'
            \""
TABLENAMES=$(export PGPASSWORD=test; eval "$PGCOMMAND")

for TABLENAME in $TABLENAMES; do
    PGCOMMAND=" psql -h localhost -U fred -d mydb -At -c \"
                SELECT   '$TABLENAME',
                         count(*) 
                FROM     $TABLENAME
                \""
    eval "$PGCOMMAND"
done
2011/04/20

Source: https://stackoverflow.com/questions/2596670
Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Email: [email protected]