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# PL/pgSQL Block Structure

**Summary**: in this tutorial, you will learn about the block structure of PL/pgSQL and how to write and execute your first PL/pgSQL block.

## Introduction to PL/pgSQL Block Structure

PL/pgSQL is a block-structured language. Here's the syntax of a block in PL/pgSQL:

```sql
[ <<label>> ]
[ declare
    declarations ]
begin
    statements;
	...
end [ label ];
```

Each block has two sections:

- Declaration
- Body

The declaration section is optional whereas the body section is required.

A block may have an optional `label` that is located at the beginning and end of the block. A block ends with a semicolon (`;`) after the `end` keyword.

Typically, you use the block label when you want to specify it in the [`EXIT`](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-exit) statement of the block body or to qualify the names of [variables](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-variables) declared in the block.

The declaration section is where you [declare all variables](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-variables) used within the body section. Each statement in the declaration section is terminated with a semicolon (`;`).

The syntax for declaring a variable is as follows:

```plsql
variable_name type = initial_value;
```

For example, the following declares a variable called `counter` with the type `int` and has an initial value of zero:

```plsql
counter int = 0;
```

Sometimes, you'll see the := operator instead of = operator. They have the same meaning:

```plsql
counter int := 0;
```

The initial value is optional. For example, you can declare a variable called `max` with the type `int` like this:

```plsql
max int;
```

Please note that you'll learn about variables in more detail in the upcoming [variable tutorial](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-variables).

The body section is where you place the code. Each statement in the body section is terminated with a semicolon (;).

## PL/pgSQL block structure example

The following example illustrates a simple block. Because the block has no name, it is called an anonymous block.

```plsql
do $$
<<first_block>>
declare
  film_count integer := 0;
begin
   -- get the number of films
   select count(*)
   into film_count
   from film;

   -- display a message
   raise notice 'The number of films is %', film_count;
end first_block $$;
```

Output:

```
NOTICE:  The number of films is 1000
DO
```

To execute a block from pgAdmin, you click the **Execute** button as shown in the following picture:

![](https://neon.com/postgresqltutorial/plpgSQL-block-Structure.png)Notice that the `DO` statement does not belong to the block. It is used to execute an anonymous block. PostgreSQL introduced the `DO` statement since version 9.0.

The anonymous block has to be surrounded by single quotes like this:

```plsql
'<<first_block>>
declare
  film_count integer := 0;
begin
   -- get the number of films
   select count(*)
   into film_count
   from film;
   -- display a message
   raise notice ''The number of films is %'', film_count;
end first_block';
```

However, we use the [dollar-quoted string constant syntax](https://neon.com/postgresql/postgresql-plpgsql/dollar-quoted-string-constants) to make it more readable.

In the declaration section, we declare a [variable](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-variables) `film_count` and initialize its value to zero.

```plsql
film_count integer = 0;
```

Inside the body section, we use a [`select into`](https://neon.com/postgresql/postgresql-plpgsql/pl-pgsql-select-into/) statement with the [`count()`](../postgresql-aggregate-functions/postgresql-count-function) function to retrieve the number of films from the `film` table and assign it to the `film_count` variable:

```sql
select count(*)
into film_count
from film;
```

After that, we show a message using [`raise notice`](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-errors-messages) statement:

```sql
raise notice 'The number of films is %', film_count;
```

The `%` is a placeholder that is replaced by the content of the `film_count` variable.

Note that the `first_block` label is just for demonstration purposes. It does nothing in this example.

## PL/pgSQL Subblocks

PL/pgSQL allows you to place a block inside the body of another block.

The block nested inside another block is called a **subblock**. The enclosing block, which contains the subblock, is often referred to as the outer block.

The following picture illustrates an outer block and subblocks:

![plpgsql block structure](https://neon.com/postgresqltutorial/plpgsql-block-structure.png)
Typically, you divide a large block into smaller, more logical subblocks. The following example illustrates how to use a subblock inside a block:

```plsql
do
$$
<<outer>>
declare
   x int = 0;
begin
   x = x + 1;
   <<inner>>
   declare
       y int = 2;
   begin
   	   y = y + x;
	   raise notice 'x=% y=%', x, y;
   end inner;
end outer;
$$
```

Output:

```
NOTICE:  x=1 y=3
DO
```

In this example, the anonymous block (outer) has a subblock (inner).

In the outer block:

- Declare a variable x and initialize its value to zero.
- Increase the value of x by one in the body.

In the inner block (subblock or nested block):

- Declare a variable y and initialize its value to zero.
- Increase the value of y by x.
- Display the values of the variables x and y using the raise notice.

## Summary

- PL/pgSQL is a blocked-structure language that organizes a program into blocks.
- A block contains two parts: declaration and body. The declaration part is optional whereas the body part is mandatory.
- Blocks can be nested. A nested block is a block placed inside the body of another block.

---

## Related docs (PostgreSQL PL/pgSQL)

- [Introduction](https://neon.com/postgresql/postgresql-plpgsql/introduction-to-postgresql-stored-procedures)
- [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)
- [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)