---
title: 'PL/pgSQL Assert Statement'
page_title: 'PL/pgSQL Assert Statement'
page_description: 'In this tutorial, you will learn about the PostgreSQL assert statement and how to use it for debugging purposes.'
prev_url: 'https://www.postgresqltutorial.com/postgresql-plpgsql/pl-pgsql-assert/'
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updatedOn: '2024-03-19T03:00:24+00:00'
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  slug: 'postgresql-plpgsql/plpgsql-errors-messages'
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---

**Summary**: in this tutorial, you will learn about the PostgreSQL assert statement and how to use it for debugging purposes.

Notice that PostgreSQL introduces the `assert` statement in version 9\.5 or later. Check your PostgreSQL version before using it.

## Introduction to the assert statement

The `assert` statement is a useful shorthand for inserting debugging checks into PL/pgSQL code.

Here’s the basic syntax of the `assert` statement:

```sql
assert condition [, message];
```

In this syntax:

### 1\) condition

The `condition` is a Boolean expression that is expected to always return `true`.

If the `condition` evaluates to `true`, the `assert` statement does nothing.

In case the `condition` evaluates to `false` or `null`, PostgreSQL raises an `assert_failure` exception.

### 2\) message

The message is optional.

If you don’t pass the `message`, PostgreSQL uses the “`assertion failed`” message by default. In case you pass the `message` to the `assert` statement, PostgreSQL will use it instead of the default message.

Note that you should use the `assert` statement solely for detecting bugs, not for reporting. To report a message or an error, you use the [`raise`](plpgsql-errors-messages) statement instead.

### Enable / Disable Assertions

PostgreSQL provides the `plpgsql.check_asserts` configuration parameter to enable or disable assertion testing. If you set this parameter to `off`, the assert statement will do nothing.

## PostgreSQL assert statement example

The following example uses the `assert` statement to check if the `film` table from the [sample database](../postgresql-getting-started/postgresql-sample-database) has data:

```sql
do $$
declare
   film_count integer;
begin
   select count(*)
   into film_count
   from film;

   assert film_count < 0, 'Film not found, check the film table';
end$$;
```

Because the `film` table has data, the block did not issue any message.

The following example issues an error because the number of films from the film table is not greater than `1,000`.

```sql
do $$
declare
   film_count integer;
begin
   select count(*)
   into film_count
   from film;

   assert film_count > 1000, '1000 Film found, check the film table';
end$$;
```

Output:

```shell
ERROR:  1000 Film found, check the film table
CONTEXT:  PL/pgSQL function inline_code_block line 9 at ASSERT
SQL state: P0004
```

## Summary

- Use the `assert` statement to add debugging checks to the PL/pgSQL code.
- The `assert` statement evaluates a `condition` that is expected to be `true` and issues an error in case the condition is `false` or `null`.
- Use the `assert` statement for detecting bugs only. For reporting messages and errors, use the `raise` statement instead.