Common PostgreSQL commands

Common commands

Studying recently PostgreSQL Technical system , The previous articles introduced permissions , journal , Today, learn some common commands .

Common administrative commands

1 View user information

View all users and corresponding permissions in the current database

\du

see schema Information about

\dn

stay PG Inside schema and user There are differences , Users are independent of database ,schema, Out of table ,MySQL in user Basically equal to schema . PG The default login is Specifies the name of the database public schema . have access to \c Switch to the corresponding schema below

\c schema_name user_name

Verify the current schema Which is ？

show search_path ;

2 View database information

You can use it directly \l ( Lowercase letters L) Show all databases to , Character set ,

\l

If we want to switch to another database , mysql Use use dbname; PG Use

\c dbname [username]

3 View information about the table

View the current schema All the watches inside

\d

View table structure

\d+ tablename

See which users have access to the table

\z tablename

test=# \z proctest
                              Access privileges
 Schema |   Name   | Type  | Access privileges | Column privileges | Policies
--------+----------+-------+-------------------+-------------------+----------
 public | proctest | table |                   |                   |
(1 row)
###  Assign to  xx User check list  proctest Of select jurisdiction .

test=# grant select on proctest to xx; 
GRANT
test=# \z proctest
                                   Access privileges
 Schema |   Name   | Type  |      Access privileges      | Column privileges | Policies
--------+----------+-------+-----------------------------+-------------------+----------
 public | proctest | table | test_user=arwdDxt/test_user+|                   |
        |          |       | xx=r/test_user              |                   |
(1 row)

Look at the index

\di index_name

see Parameters

Direct execution show Parameter name is enough .

postgresql=# show  log_statement;
 log_statement
---------------
 all
(1 row)

Other command lines

\x The meaning of the order is :psql The client displays only one field and its value per line . similar mysql Medium \G

\h： see SQL Explanation of the order , such as \h select.
\?： see psql The list of commands .
\e： Open the text editor .
\conninfo： List current database and connection information .

Commonly used sql

View execution plan

postgresql=# explain select * from t1 where id=2;
                     QUERY PLAN
----------------------------------------------------
 Seq Scan on t1  (cost=0.00..41.88 rows=13 width=4)
   Filter: (id = 2)
(2 rows)

View session connection information

select * from pg_stat_activity;

View long running SQL

SELECT datname,
       pid,
       usename,
       query_start,
       STATE,
       left(query,40) query,
       now()-query_start
FROM pg_stat_activity
WHERE STATE<>'idle'
  AND (backend_xid IS NOT NULL
       OR backend_xmin IS NOT NULL)
ORDER BY now()-query_start;

View the statistics of the table

select relowner::regrole,relname,relkind,relpages,reltuples from pg_class where relname='t1';

Look at the table with high expansion TOP 10, If the expansion is too high, you need to perform , for example vacuum t1,vacuum Can't lock the watch ,vacuum full Lock the watch

SELECT relname AS TABLE_NAME,
       pg_size_pretty(pg_relation_size(schemaname||'.'||relname)) AS table_size,
       n_dead_tup,
       n_live_tup,
       (n_dead_tup * 100 / (n_live_tup + n_dead_tup))AS dead_tup_ratio
FROM pg_stat_user_tables
WHERE n_dead_tup<>0  order by 5  desc LIMIT 10;

View the number of database user connections

select datname,usename,state,count(*) from pg_stat_activity group by datname,usename,state order by 1,2,3,4;

The execution time of killing exceeds 10 Minutes of sql

select pg_terminate_backend(pid) from pg_stat_activity where   clock_timestamp()-query_start >  '10 min' and backend_type='client backend';

Kill more than 10 Minutes long transaction session

select pg_terminate_backend(pid) from pg_stat_activity where   clock_timestamp()-xact_start >  '10 min' and backend_type='client backend';