Get the Size of Multiple Tables in One Query POSTGRES?

问题

Following on from this prior question about relation sizes:

This query:

query = "CREATE TEMPORARY TABLE query_out AS SELECT * FROM users WHERE is_admin = false"
ActiveRecord::Base.connection.execute(query)

will generate a temporary table and insert all the records from this query i.e

SELECT * FROM users WHERE is_admin = false

then

ActiveRecord::Base.connection.execute("SELECT pg_size_pretty(pg_relation_size('query_out'))")

I am only getting the the size of one table.

What doI need to do so that I can the size of multiple tables in one single query?

Any help would be appreciated.

Thanks

It will give the size of that temporary table.

回答1:

Following select query will returns all the table and its size's

SELECT
   relname as mytable,
   pg_size_pretty(pg_relation_size(relid)) As size
   FROM pg_catalog.pg_statio_user_tables ORDER BY pg_total_relation_size(relid) DESC;

Create a VIEW with this select

CREATE VIEW vTableAndSize AS 
SELECT
   relname as mytable,
   pg_size_pretty(pg_relation_size(relid)) As size
   FROM pg_catalog.pg_statio_user_tables ORDER BY pg_total_relation_size(relid) DESC;

and now you can query on this view to get the size like this

SELECT mytable,size 
       FROM vTableAndSize WHERE mytable in ('table1','table2')

As per OP's Comment

CREATE VIEW vTableAndSize_1 as 
SELECT
   relname as mytable,
   (pg_relation_size(relid)) As size
   FROM pg_catalog.pg_statio_user_tables ORDER BY pg_total_relation_size(relid) DESC;

and get the size sum of multiple columns using

/* Get sum of specific tables */
SELECT pg_size_pretty(sum(size)) tablesizesum 
       FROM vTableAndSize_1 WHERE mytable in ('table1','table2')

/* Get sum of all tables */
SELECT pg_size_pretty(sum(size)) tablesizesum 
       FROM vTableAndSize_1

Create vTableAndSize_1 in your PostgreSQL database and query like below in your front end(am not familiar with Ruby)

ActiveRecord::Base.connection.execute("SELECT pg_size_pretty(sum(size)) FROM vTableAndSize_1 
WHERE mytable in ('table1','table2')")

来源：https://stackoverflow.com/questions/27054654/get-the-size-of-multiple-tables-in-one-query-postgres

标签

postgresql

ruby-on-rails-4

ruby-2.0