Tutorials

Postgres useful commands

Posted on 30-Jul-2018

Here are some examples of commands to use with postgres and the equivalent to MySQL:

SHOW TABLES

  • CLI: \d
  • SQL: SELECT tablename FROM informationschema.tables WHERE table_schema = 'public';

SHOW DATABASES

  • CLI: \l
  • SQL: SELECT datname FROM pg_database;

SHOW COLUMNS

  • CLI: \d table
  • SQL: SELECT columnname FROM informationschema.columns WHERE table_name ='table';

DESCRIBE TABLE

  • CLI: \d+ table
  • SQL: SELECT columnname FROM informationschema.columns WHERE table_name ='table';

CREATE DATABASE

CREATE DATABASE dbName;

CREATE TABLE (with auto numbering integer id)

CREATE TABLE tableName (
 id serial PRIMARY KEY,
 name varchar(50) UNIQUE NOT NULL,
 dateCreated timestamp DEFAULT current_timestamp
);

Add a primary key

ALTER TABLE tableName ADD PRIMARY KEY (id);

Create an INDEX

CREATE UNIQUE INDEX indexName ON tableName (columnNames);

Backup a database (command line)

pg_dump dbName > dbName.sql

Backup all databases (command line)

pg_dumpall > pgbackup.sql

Run a SQL script (command line)

psql -f script.sql databaseName

Search using a regular expression

SELECT column FROM table WHERE column ~ 'foo.*';

The first N records

SELECT columns FROM table LIMIT 10;

Pagination

SELECT cols FROM table LIMIT 10 OFFSET 30;

Prepared Statements

PREPARE preparedInsert (int, varchar) AS
  INSERT INTO tableName (intColumn, charColumn) VALUES ($1, $2);
EXECUTE preparedInsert (1,'a');
EXECUTE preparedInsert (2,'b');
DEALLOCATE preparedInsert;

Create a Function

CREATE OR REPLACE FUNCTION month (timestamp) RETURNS integer 
 AS 'SELECT date_part(''month'', $1)::integer;'
LANGUAGE 'sql';

Table Maintenance

VACUUM ANALYZE table;

Reindex a database, table or index

REINDEX DATABASE dbName;

Show query plan

EXPLAIN SELECT * FROM table;

Explain analyze

EXPLAIN ANALYZE
SELECT *
FROM table

Import from a file

COPY destTable FROM '/tmp/somefile';

Show all runtime parameters

SHOW ALL;

Grant all permissions to a user

GRANT ALL PRIVILEGES ON table TO username;

Perform a transaction

BEGIN TRANSACTION 
 UPDATE accounts SET balance += 50 WHERE id = 1;
COMMIT;

Get all columns and rows from a table

SELECT * FROM table;

Add a new row

INSERT INTO table (column1,column2)
VALUES (1, 'one');

Update a row

UPDATE table SET foo = 'bar' WHERE id = 1;

Delete a row

DELETE FROM table WHERE id = 1;

List tables owners

SELECT * FROM pg_tables 
WHERE schemaname = 'my_name';

Change table owner

ALTER TABLE schema_name.table_name OWNER TO username_or_role;