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# PL/pgSQL Assert Statement

**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`](https://neon.com/postgresql/postgresql-plpgsql/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:

```plsql
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`.

```plsql
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:

```
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.

---

## Related docs (PostgreSQL PL/pgSQL)

- [Introduction](https://neon.com/postgresql/postgresql-plpgsql/introduction-to-postgresql-stored-procedures)
- [Block Structure](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-block-structure)
- [Variables](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-variables)
- [Constants](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-constants)
- [IF-ELSE Statements](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-if-else-statements)
- [CASE Statement](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-case-statement)
- [Loop Statements](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-loop-statements)
- [FOR Loop](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-for-loop)
- [WHILE Loop](https://neon.com/postgresql/postgresql-plpgsql/pl-pgsql-while-loop)
- [EXIT Statement](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-exit)
- [CONTINUE Statement](https://neon.com/postgresql/postgresql-plpgsql/pl-pgsql-continue)
- [Cursor](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-cursor)
- [Function Parameters](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-function-parameters)
- [Function Overloading](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-function-overloading)
- [Function Returns Table](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-function-returns-a-table)
- [Returns SETOF](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-returns-setof)
- [Record Types](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-record-types)
- [Row Types](https://neon.com/postgresql/postgresql-plpgsql/pl-pgsql-row-types)
- [Error Messages](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-errors-messages)
- [Exception Handling](https://neon.com/postgresql/postgresql-plpgsql/postgresql-exception)
- [CREATE FUNCTION](https://neon.com/postgresql/postgresql-plpgsql/postgresql-create-function)
- [CREATE PROCEDURE](https://neon.com/postgresql/postgresql-plpgsql/postgresql-create-procedure)
- [DROP FUNCTION](https://neon.com/postgresql/postgresql-plpgsql/postgresql-drop-function)
- [DROP PROCEDURE](https://neon.com/postgresql/postgresql-plpgsql/postgresql-drop-procedure)
- [Stored Procedure with INOUT Parameters](https://neon.com/postgresql/postgresql-plpgsql/postgresql-stored-procedure-with-inout-parameters)
- [Introduction to Stored Procedures](https://neon.com/postgresql/postgresql-plpgsql/introduction-to-postgresql-stored-procedures)
- [SELECT INTO](https://neon.com/postgresql/postgresql-plpgsql/pl-pgsql-select-into)
- [Dollar-Quoted String Constants](https://neon.com/postgresql/postgresql-plpgsql/dollar-quoted-string-constants)