PostgreSQL - Day 2

• Tue, Jun 7, 2022
• One-minute read

Learn PostgreSQL - Day 2

Keep learning PostgreSQL by Learn PostgreSQL Tutorial - Full Course for Beginners.

7. How to Create Database

• get help with help
• list databases \l
• create database

  CREATE DATABASE test;
  

• tip: using UPPERCASE syntax for SQL commands can increase readablility

8. How to Connect to Database

1. connection with psql

psql -h localhost -p 5432 -U <username> <database_name>

2. in psql, call \c command to connect database

9. A Very Dangerous Command

DROP DATABASE [name];

This command will delete all the data in the database and itself.

10. Creating Tables Without Constraints

CREATE TABLE table_name (
	<column name> <data type> [constrains]
)

• check tables in database \d

• check description of table \d <table name>

all data types supported by Postgres

https://www.postgresql.org/docs/current/datatype.html

11. Creating Tables with Constraints

Specify constraints to avoid inserting an incomplete entry.

• NOT NULL
• PRIMARY KEY

There is a person_id_seq sequence. This sequence is for BIGSERIAL remembering the current value.

\dt to show table only

12. How to insert records into tables

1. use INSERT INTO command
2. specify the columns we want to insert.
3. Set values by an array of values matching the columns

You don’t have to manage the value of auto-incremental columns.

• What does 0 1 means? It’s oid and count, spec
  • oid is a deprecate feature.