SQL

PSQL get version

psql -h <IP/DNS> -U <user> -d <database> -c 'SELECT VERSION()'

PSQL test connection

Install packages postgresql-client-common and postgresql-client-10

psql -h <host> -p <port> -U <username> -d <database> -c '\c'

Database size

SELECT pg_size_pretty( pg_database_size('<database>') );

Table sizes

select table_name, pg_size_pretty( pg_relation_size(quote_ident(table_name)) )
from information_schema.tables
where table_schema = 'public'
order by pg_relation_size(quote_ident(table_name)) desc;

Mysql change user password

mysql -u username-p
use mysql;
update user set password=PASSWORD('your_new_password') where User='username';
flush privileges;
quit

Postgres automatically fit records to the width of the screen(add to ~/.psqlrc to start psql with it every time)

\x auto

Postgres query from bash

psql -U <username> -d <database> -c "select * from ppl;"

Mssql list all tables

select * from sys.all_objects where type = 'U'

Oracle list all users

select username from dba_users