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# PL/pgSQL IF Statement

**Summary**: in this tutorial, you will learn how to use the PL/pgSQL `if` statements to execute a command based on a specific condition.

## Introduction to PL/pgSQL IF Statement

The `if` statement allows you to execute one or more statements based on a condition. PL/pgSQL provides you with three forms of the `if` statements:

1. `if then`
2. `if then else`
3. `if then elsif`

### 1) PL/pgSQL if-then statement

The following illustrates the simplest form of the `if` statement:

```plsql
if condition then
   statements;
end if;
```

The `if` statement executes `statements` when a `condition` is true. If the `condition` evaluates to `false`, the control is passed to the next statement after the `end if` .

The `condition` is a boolean expression that evaluates to `true` or `false`.

The `statements` can be one or more statements that you want to execute when the `condition` is true. It may contain other `if` statements.

When you place an `if` statement is within another `if` statement, you'll have a nested-if statement.

The following flowchart illustrates the simple `if` statement.

[![PL/pgSQL if statement](https://neon.com/postgresqltutorial/plpgsql-if-statement.png)](https://neon.com/postgresqltutorial/plpgsql-if-statement.png)The following example uses an `if` statement to check if a query returns any rows:

```plsql
do $$
declare
  selected_film film%rowtype;
  input_film_id film.film_id%type = 0;
begin

  select * from film
  into selected_film
  where film_id = input_film_id;

  if not found then
     raise notice'The film % could not be found',
	    input_film_id;
  end if;
end $$;
```

Output:

```
NOTICE:  The film 0 could not be found

```

In this example, we select a film by a specific film id (`0`).

The `found` is a global variable that is available in PL/pgSQL. The [`select into`](https://neon.com/postgresql/postgresql-plpgsql/pl-pgsql-select-into/) statement sets the `found` variable if a row is assigned or `false` if no row is returned.

We use the `if` statement to check if the film with id (0) exists and raise a notice if it does not.

```plsql
if not found then
   raise notice'The film % could not be found', input_film_id;
end if;
```

If you change the value of the `input_film_id` variable to some value that exists in the film table like 100, you will not see any message.

### 2) PL/pgSQL if-then-else statement

The `if...then...else` statement executes the statements in the `if` branch if the `condition` evaluates to true; otherwise, it executes the statements in the `else` branch.

Here's the syntax of the `if...then...else` statement:

```plsql
if condition then
  statements;
else
  alternative-statements;
end if;
```

The following flowchart illustrates the `if else` statement.

![PL/pgSQL if else statement](https://neon.com/postgresqltutorial/plpgsql-if-else-statement.png)
The following example uses an if…then…else statement to display a message showing that a film with a specific id exists or not:

```plsql
do $$
declare
  selected_film film%rowtype;
  input_film_id film.film_id%type := 100;
begin

  select * from film
  into selected_film
  where film_id = input_film_id;

  if not found then
     raise notice 'The film % could not be found',
	    input_film_id;
  else
     raise notice 'The film title is %', selected_film.title;
  end if;
end $$;
```

Output:

```
NOTICE:  The film title is Brooklyn Desert
```

In this example, because the film id 100 exists in the film table the `found` variable is true. Therefore, the statement in the `else` branch is executed.

### 3) PL/pgSQL if-then-elsif Statement

Unlike the `if` and `if...then...else` statements that evaluate only one condition, the `if then elsif` statement allows you to evaluate multiple conditions. and execute one or more statements when a condition is true.

Here's the syntax of the `if...then...elsif` statement:

```plsql
if condition_1 then
  statement_1;
elsif condition_2 then
  statement_2
...
elsif condition_n then
  statement_n;
else
  else-statement;
end if;
```

In this syntax, if the `condition_1` is `true` then the `if...then...elsif` statement executes the `statement_1` and stops evaluating the other conditions such as `condition_2`, `condition_3`, and so on.

If all conditions are evaluated to `false`, the `if...then...elsif` executes the statements in the `else` branch.

The following flowchart illustrates the `if then elsif` statement:

![PL/pgSQL if ELSif else Statement](https://neon.com/postgresqltutorial/if-elsif-else-statement.png)
Let's look at the following example:

```plsql
do $$
declare
   v_film film%rowtype;
   len_description varchar(100);
begin

  select * from film
  into v_film
  where film_id = 100;

  if not found then
     raise notice 'Film not found';
  else
      if v_film.length >0 and v_film.length <= 50 then
		 len_description := 'Short';
	  elsif v_film.length > 50 and v_film.length < 120 then
		 len_description := 'Medium';
	  elsif v_film.length > 120 then
		 len_description := 'Long';
	  else
		 len_description := 'N/A';
	  end if;

	  raise notice 'The % film is %.',
	     v_film.title,
	     len_description;
  end if;
end $$;
```

Output:

```
NOTICE:  The Brooklyn Desert film is Long.
```

How it works:

- First, select the film with id 100. If the film does not exist, raise a notice that the film is not found.
- Second, use the `if...then....elsif` statement to assign a description to a film based on the length of the film.

## Summary

- Use the `if..then` statement to execute one or more statements when a condition is `true`.
- Use the `if...then...else` statement to execute statements when a condition is `true` and execute other statements when the condition is `false`.
- Use the `if...then...elsif` statement to evaluate multiple conditions and execute statements when the corresponding condition is `true`.

---

## 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)
- [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)
- [ASSERT Statement](https://neon.com/postgresql/postgresql-plpgsql/pl-pgsql-assert)
- [Dollar-Quoted String Constants](https://neon.com/postgresql/postgresql-plpgsql/dollar-quoted-string-constants)