PostgreSQL – Cheat Sheet

30 Jun, 2021
PostgreSQL is a powerful, open-source object-relational database system that aimed to help developers build applications, administrators to protect data integrity and build fault-tolerant environments. It supports advanced data types and performance optimization features, like Ms-SQL Server and Oracle.
Open Source DBMS
Supports ACID properties
Diverse indexing techniques
Log-based and trigger-based replication SSL
Support for JSON
Supports geographic objects
Object-oriented and ANSI-SQL 2008 compatible
The following table list all the data types available in PostgreSQL:
PostgreSQL Data Types
Numeric Data types: smallint, integer, bigint, decimal, numeric, real, serial.
Character Data types: varchar(n), text, char(n).
Date/Time Data types: timestamp, date, time, interval.
Monetary Data type: money.
Binary Data type: bytea (supports hex and escape format).
Boolean Data type: boolean.
Geometric Data types: point, line, box, path, polygon, circle, lseg.
JSON Data types: string, number, boolean, null.
Enumerated Data types: enum.
UUID Data type: uuid (stores Universally Unique Identifiers).
Network Address types: cidr, inet, macaddr.
Pseudo types: any, anyelement, anyarray, anyenum, anyrange, internal, record, trigger, event_trigger.
BitString types: bit(n), bit varying(n).
Range Data types: int4range, int8range, numrange, tsrange (timestamp range), daterange.
pg_lsn type: pg_lsn (stores Log Sequence Number).
An operator manipulates individual data items and returns a result. These are the reserved words used in WHERE clause to perform operations.
Operators
To install PostgreSQL, run the following command:
sudo apt install postgresql

OR

sudo apt install postgresql postgresql-contrib
The postgresql-contrib will add some additional utilities and functionalities.
After installation, switch over to the Postgres account:
sudo -i -u postgres
Now, you can access the Postgres prompt using psql command.
The CREATE DATABASE command is used to create the database.
Syntax:
CREATE DATABASE database_name;
Example:
Create Database
Now, to store the data, we need the table. The CREATE TABLE statement is used to create the table.
Syntax:
CREATE TABLE table_name
(column_1 data_type,
column_2 data_type,
...
column_n data_type);
Example: 
Create table
The INSERT command is used to insert the new record (row) into the table.
Syntax: 
INSERT INTO table_name (column_1, column_2 ,...)
VALUES(value_1, value_2, ...);
Example:  
Insert into table
The SELECT statement is used to fetch the data from a database table, which returns the data in the form of a result table.
Syntax: 
SELECT  
column_1, column_2, .. column_n
FROM
table_name;
Example:
Select command
Note: We can fetch all the fields of the table using an asterisk(*) sign.
The WHERE clause is used to filter results returned by the SELECT statement.
Syntax:
SELECT column_name
FROM 
table_name 
WHERE condition;
Example:
Where clause
The LIMIT clause is used to get a subset of rows generated by a query. It is an optional clause of the SELECT statement. OFFSET n skips ‘n’ rows before beginning to return rows.
Syntax:
SELECT * 
FROM table_name 
LIMIT n;
Example:
Limit & Offset
The structure of an existing table can be modified using the ALTER TABLE statement. PostgreSQL supports the various actions to perform with ALTER TABLE as listed below:
Add a column to an existing table
ALTER TABLE table_name ADD COLUMN new_column_name TYPE;
Drop a column from an existing table
ALTER TABLE table_name DROP COLUMN column_name;
Rename a column from an existing table
ALTER TABLE table_name RENAME COLUMN column_name TO new_column_name;
Rename a column from an existing table
ALTER TABLE table_name ALTER COLUMN column_name [SET DEFAULT value | DROP DEFAULT];
Change NOT NULL constraint
ALTER TABLE table_name ALTER COLUMN column_name [SET NOT NULL| DROP NOT NULL];
Add CHECK constraints to a column
ALTER TABLE table_name ADD CHECK expression;
Add a constraint
ALTER TABLE table_name ADD CONSTRAINT constraint_name constraint_definition;
Rename an existing table
ALTER TABLE table_name RENAME TO new_table_name;
The UPDATE statement is used to update or modify existing data in the table.
Syntax:
UPDATE table_name
SET column_1 = value_1,
   column_2 = value_2, ...
WHERE
   condition_1 AND condition_2;
Example:
Update
The DELETE statement is used to delete the row(s) from the table.
Syntax:
DELETE FROM table_name
WHERE condition;
Example:
Delete
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PostgreSQL
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PostgreSQL - LIMIT with OFFSET clause
PostgreSQL - REPLACE Function
PostgreSQL - DROP INDEX
PostgreSQL - INSERT
PostgreSQL - TIME Data Type
PostgreSQL - ROW_NUMBER Function
PostgreSQL - SELECT
PostgreSQL - CREATE SCHEMA
PostgreSQL - EXISTS Operator
PostgreSQL - LEFT JOIN