Potsgresql: handy commands

PostgreSQL handy commands

-- Viewing current PostgreSQL queries
-- source: http://chrismiles.info/systemsadmin/databases/articles/viewing-current-postgresql-queries/
SELECT datname,pid,query,query_start FROM pg_stat_activity ORDER BY query_start ASC;

-- top-like view of current queries, grouped by how many of the same query are running at that instant and the usernames belonging to each connection.
SELECT count(*) as cnt, usename, current_query FROM pg_stat_activity GROUP BY usename,current_query ORDER BY cnt DESC;

-- List databases creation dates
SELECT (pg_stat_file('base/'||oid ||'/PG_VERSION')).modification, datname FROM pg_database ORDER BY modification;
SELECT (pg_stat_file('base/'||oid ||'/PG_VERSION')).modification, datname FROM pg_database ORDER BY datname;

-- List tables in a particular schema
\dt schemaname.*

-- Change postgres password
  $ sudo -u postgres psql postgres
  postgres=# \password postgres

-- Export a table to a csv file
COPY tablename TO '/tmp/filename.csv' HEADER CSV; 

-- Import a csv file with null values integer
COPY public."tablename" FROM '/path/file.csv' USING DELIMITERS ',' csv NULL AS '';

-- Drop all tables
SELECT 'DROP table IF EXISTS "' || tablename || '" CASCADE;' 
FROM pg_tables
WHERE schemaname = 'public';
--------------------------------------
-- drop table if exists "tab1" cascade;
-- drop table if exists "tab2" cascade;
-- (2 rows)

-- Modify owner (getest)
SELECT format(
  'ALTER TABLE %I.%I.%I OWNER TO %I;',
  table_catalog,
  table_schema,
  table_name,
  current_user  -- or another just put it in quotes
)
FROM information_schema.tables
WHERE table_schema = 'mySchema';
In psql, you can run them by following it immediately with \gexec

-- Modify owner on all tables
for tbl in `psql -Upostgres -hlocalhost -qAt -c "select tablename from pg_tables where schemaname = 'public';" YOUR_DB` ; do psql -Upostgres -hlocalhost -c "alter table $tbl owner to NEW_OWNER" YOUR_DB ; done

-- Modify owner on all sequences
for tbl in `psql -Upostgres -hlocalhost -qAt -c "select sequence_name from information_schema.sequences where sequence_schema = 'public';" YOUR_DB` ; do  psql -Upostgres -hlocalhost -c "alter table $tbl owner to NEW_OWNER" YOUR_DB ; done

-- zie https://gist.github.com/gingerlime/2482969 - change_db_owner.sh

-- Listing the number of records in all postgresql tables 
(source: http://linfiniti.com/2011/06/listing-the-number-of-records-in-all-postgresql-tables)
$ for TABLE in $(psql foo-test -c "\dt" | awk '{print $3}')
do 
psql foo-test -c "select '$TABLE', count(*) from $TABLE;" | grep -A1 "\-\-\-\-" | tail -1
done

-- change owner
REASSIGN OWNED BY old_role [, ...] TO new_role

# create read-only user
# source: https://blog.ed.gs/2016/01/12/add-read-only-postgres-user/
psql databasehere
CREATE USER moodle_readonly WITH ENCRYPTED PASSWORD 'blablablapasswordhere';
GRANT CONNECT ON DATABASE moodle TO moodle_readonly;
GRANT USAGE ON SCHEMA public TO moodle_readonly;
GRANT SELECT ON ALL SEQUENCES IN SCHEMA public TO moodle_readonly;
GRANT SELECT ON ALL TABLES IN SCHEMA public to moodle_readonly;
ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO moodle_readonly;