# SQL, Handling empty cells

> Learn how to handle null and empty cells in a SQL database, and how to prevent them by adding the NOT NULL constraint to your table columns.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2020-03-29 | Topics: [Database](https://flaviocopes.com/tags/database/) | Canonical: https://flaviocopes.com/sql-null/

When we create a table in this way:

```sql
CREATE TABLE people (
  age INT,
  name CHAR(20)
);
```

SQL freely accepts empty values as records:

```sql
INSERT INTO people VALUES (null, null);
```

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

```
 age |  name  
-----+--------
  37 | Flavio
   8 | Roger
     | 
```

To solve this, we can declare constrains on our table rows. `NOT NULL` prevents null values:

```sql
CREATE TABLE people (
  age INT NOT NULL,
  name CHAR(20) NOT NULL
);
```

If we try to execute this query again:

```sql
INSERT INTO people VALUES (null, null);
```

We'd get an error, like this:

```
ERROR:  null value in column "age" violates not-null constraint
DETAIL:  Failing row contains (null, null).
```

> Note that an empty string is a valid non-null value.