DECLARE

MySQL

Example

DECLARE @MyVar int;
SET @MyVar = 5;
SELECT @MyVar AS 'Value';

Output

| Value |
|-------|
| 5     |

Explanation

In the given example, a declaration of an integer variable @MyVar is made, and it is set to 5. The SELECT statement is then used to display the value of @MyVar.

PostgreSQL

# Example

```sql
DECLARE @animal VARCHAR(20);
SET @animal = 'Lion';
SELECT @animal as Animal;

Output

Animal
Lion

Explanation

In the example code, a variable named ‘@animal’ is declared with the type of ‘VARCHAR(20)’. Then, the variable ‘@animal’ is set to hold the value as ‘Lion’. Finally, the data stored in ‘@animal’ is selected and returned, which will give us the output of ‘Lion’.

SQL Server

Example

DECLARE @FirstName nvarchar(50);
SET @FirstName = 'John';
SELECT @FirstName AS 'First Name';

Output

First Name
----------
John

Explanation

In the provided SQL Server example, the DECLARE keyword is used to create a variable named @FirstName of type nvarchar(50). The SET keyword is then used to assign the value ‘John’ to the @FirstName variable. Finally, the SELECT statement is used to display the value of @FirstName.

Oracle

Example

DECLARE
   Value_1 NUMBER;
BEGIN
   Value_1 := 10;
   DBMS_OUTPUT.PUT_LINE ('The value of Variable Number is ' || Value_1);
END;

Output

The value of Variable Number is 10

Explanation

In the above SQL script, a variable ‘Value_1’ of type NUMBER is declared. Subsequently, a value of 10 is assigned to this variable. Finally, the value of the variable is output using the DBMS_OUTPUT.PUT_LINE command. This output is displayed under the shell.