1. 技术文章
  2. How do you find the row count for all your tables in Postgres

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

由 淺唱寂寞╮ 提交于 2020-01-06 07:14:35

问题


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.


回答1:


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.




回答2:


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.




回答3:


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.




回答4:


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;



回答5:


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
[..]



回答6:


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



回答7:


I usually don't rely on statistics, especially in PostgreSQL.

SELECT table_name, dsql2('select count(*) from '||table_name) as rownum
FROM information_schema.tables
WHERE table_type='BASE TABLE'
    AND table_schema='livescreen'
ORDER BY 2 DESC;

CREATE OR REPLACE FUNCTION dsql2(i_text text)
  RETURNS int AS
$BODY$
Declare
  v_val int;
BEGIN
  execute i_text into v_val;
  return v_val;
END; 
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;



回答8:


I don't remember the URL from where I collected this. But hope this should help you:

CREATE TYPE table_count AS (table_name TEXT, num_rows INTEGER); 

CREATE OR REPLACE FUNCTION count_em_all () RETURNS SETOF table_count  AS '
DECLARE 
    the_count RECORD; 
    t_name RECORD; 
    r table_count%ROWTYPE; 

BEGIN
    FOR t_name IN 
        SELECT 
            c.relname
        FROM
            pg_catalog.pg_class c LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
        WHERE 
            c.relkind = ''r''
            AND n.nspname = ''public'' 
        ORDER BY 1 
        LOOP
            FOR the_count IN EXECUTE ''SELECT COUNT(*) AS "count" FROM '' || t_name.relname 
            LOOP 
            END LOOP; 

            r.table_name := t_name.relname; 
            r.num_rows := the_count.count; 
            RETURN NEXT r; 
        END LOOP; 
        RETURN; 
END;
' LANGUAGE plpgsql;

Executing select count_em_all(); should get you row count of all your tables.




回答9:


I made a small variation to include all tables, also for non-public tables.

CREATE TYPE table_count AS (table_schema TEXT,table_name TEXT, num_rows INTEGER); 

CREATE OR REPLACE FUNCTION count_em_all () RETURNS SETOF table_count  AS '
DECLARE 
    the_count RECORD; 
    t_name RECORD; 
    r table_count%ROWTYPE; 

BEGIN
    FOR t_name IN 
        SELECT table_schema,table_name
        FROM information_schema.tables
        where table_schema !=''pg_catalog''
          and table_schema !=''information_schema''
        ORDER BY 1,2
        LOOP
            FOR the_count IN EXECUTE ''SELECT COUNT(*) AS "count" FROM '' || t_name.table_schema||''.''||t_name.table_name
            LOOP 
            END LOOP; 

            r.table_schema := t_name.table_schema;
            r.table_name := t_name.table_name; 
            r.num_rows := the_count.count; 
            RETURN NEXT r; 
        END LOOP; 
        RETURN; 
END;
' LANGUAGE plpgsql;

use select count_em_all(); to call it.

Hope you find this usefull. Paul




回答10:


Simple Two Steps:
(Note : No need to change anything - just copy paste)
1. create function

create function 
cnt_rows(schema text, tablename text) returns integer
as
$body$
declare
  result integer;
  query varchar;
begin
  query := 'SELECT count(1) FROM ' || schema || '.' || tablename;
  execute query into result;
  return result;
end;
$body$
language plpgsql;

2. Run this query to get rows count for all the tables

select sum(cnt_rows) as total_no_of_rows from (select 
  cnt_rows(table_schema, table_name)
from information_schema.tables
where 
  table_schema not in ('pg_catalog', 'information_schema') 
  and table_type='BASE TABLE') as subq;

or

To get rows counts tablewise

select
  table_schema,
  table_name, 
  cnt_rows(table_schema, table_name)
from information_schema.tables
where 
  table_schema not in ('pg_catalog', 'information_schema') 
  and table_type='BASE TABLE'
order by 3 desc;



回答11:


I like Daniel Vérité's answer. But when you can't use a CREATE statement you can either use a bash solution or, if you're a windows user, a powershell one:

# You don't need this if you have pgpass.conf
$env:PGPASSWORD = "userpass"

# Get table list
$tables = & 'C:\Program Files\PostgreSQL\9.4\bin\psql.exe' -U user -w -d dbname -At -c "select table_name from information_schema.tables where table_type='BASE TABLE' AND table_schema='schema1'"

foreach ($table in $tables) {
    & 'C:\path_to_postresql\bin\psql.exe' -U root -w -d dbname -At -c "select '$table', count(*) from $table"
}



回答12:


This worked for me

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




回答13:


I wanted the total from all tables + a list of tables with their counts. A little like a performance chart of where most time was spent

WITH results AS ( 
  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'
     GROUP BY schemaname, relname, reltuples
)

SELECT * FROM results
UNION
SELECT 'all' AS schemaname, 'all' AS relname, SUM(reltuples) AS "reltuples" FROM results

ORDER BY reltuples DESC

You could of course put a LIMIT clause on the results in this version too so that you get the largest n offenders as well as a total.

One thing that should be noted about this is that you need to let it sit for a while after bulk imports. I tested this by just adding 5000 rows to a database across several tables using real import data. It showed 1800 records for about a minute (probably a configurable window)

This is based from https://stackoverflow.com/a/2611745/1548557 work, so thank you and recognition to that for the query to use within the CTE



来源：https://stackoverflow.com/questions/49263515/create-cursor-for-dynamic-table-search-postgresql

标签
postgresql
count
database-table
易学教程内所有资源均来自网络或用户发布的内容，如有违反法律规定的内容欢迎反馈！
该文章没有解决你所遇到的问题?点击提问,说说你的问题,让更多的人一起探讨吧!