When we create a table in this way:

CREATE TABLE people (
  age INTEGER,
  name TEXT
);

SQL freely accepts empty values as records:

INSERT INTO people VALUES (null, null);

This might be a problem, because now we have a row with null values:

To solve this, we can declare constraints on our table columns. NOT NULL prevents null values:

DROP TABLE people;

CREATE TABLE people (
  age INTEGER NOT NULL,
  name TEXT NOT NULL
);

If we try to execute this query again:

INSERT INTO people VALUES (null, null);

We’d get an error, like this:

This is an example of the DBMS setting boundaries on the data we insert.

Very helpful for keeping the data clean.

Lessons in this unit:

0:	Introduction
1:	Using TablePlus
2:	Create a Postgres database
3:	Create a new table
4:	Add data to a table
5:	Query data with SELECT
6:	Delete data from the database
7:	Update data with UPDATE
8:	▶︎ Null constraints
9:	Unique and primary keys
10:	Updating a table structure
11:	Joins
12:	SQL Views
13:	SQL, copy data from one table to another