Postgresql Cheat Sheet

PostgreSQL commands

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PostgreSQL Cheat Sheet

Each table is made up of rows and columns. If you think of a table as a grid, the column go from left to right across the grid and each entry of data is listed down as a row.

ALLOFMYOTHERARTICLES bryanguner.medium.com

Each row in a relational is uniquely identified by a primary key. This can be by one or more sets of column values. In most scenarios it is a single column, such as employeeID.

Every relational table has one primary key. Its purpose is to uniquely identify each row in the database. No two rows can have the same primary key value. The practical result of this is that you can select every single row by just knowing its primary key.

SQL Server UNIQUE constraints allow you to ensure that the data stored in a column, or a group of columns, is unique among the rows in a table.

Although both UNIQUE and PRIMARY KEY constraints enforce the uniqueness of data, you should use the UNIQUE constraint instead of PRIMARY KEY constraint when you want to enforce the uniqueness of a column, or a group of columns, that are not the primary key columns.

Different from PRIMARY KEY constraints, UNIQUE constraints allow NULL. Moreover, UNIQUE constraints treat the NULL as a regular value, therefore, it only allows one NULL per column.

Create a new role:

CREATE ROLE role_name;

Create a new role with a username and password: