not-null constraint in Postgresql

A not-null constraint makes sure that a column must have some values and a value is not left as null. Drop the previously created tools table and create the tools table again using this constraint using the following example:

warehouse_db=# CREATE TABLE tools ( tool_id INTEGER NOT NULL, tool_name TEXT, tool_class NUMERIC ); 

The preceding query will create a table with a not-null constraint on the tool_id column. We can apply the not-null constraint on as many columns as we can. Consider the following example:

warehouse_db=# CREATE TABLE tools ( tool_id INTEGER NOT NULL, tool_name TEXT NOT NULL, tool_class NUMERIC ); 

The preceding query will create the tools table with not-null constraints on tool_id and tool_name.

In the next article, we'll discuss Exclusion constraints in postgresql.