#   
## What is SQL?

**Structured Query Language (SQL)** is a language that is used to access and manipulate databases. With the help of SQL queries, we can store data in the database in an accessible form, easily retrieve it, and update it whenever needed. 
Some basic and common SQL commands are `INSERT`, `SELECT`, `UPDATE`, `DELETE`, `WHERE`, etc.

Similarly to functions that we make so that code can be used again, we have **stored procedures** in SQL.

#   
## Stored procedures

In SQL, a **stored procedure** is a prepared SQL code that developers can save so that the code can be easily reused later.


If we have SQL code that needs to be used many times, we can store it as stored procedures and call it whenever necessary. We can also pass parameters to the stored procedures, just like in functions, to make it more customizable.

## Syntax


CREATE PROCEDURE SQL_procedure_name
AS
SQL_statements
GO;

The code above shows us how to create a stored procedure. To create a stored procedure, you can use the `CREATE PROCEDURE` statement followed by the stored procedure name. Then, after the `AS` statement, we write all the SQL queries/code that needs to be reused and conclude the stored procedure with the `GO` statement. Below is the code to call/execute the stored procedure.

#    
## Example
Consider the following database named *information*. 


CREATE TABLE information (
 -- <Variable name> <Variable type>
 Name 	varchar(255),
 Age 		varchar(255),
 Gender 		varchar(255),
 City 		varchar(255)
);

INSERT INTO

 information 
 
 (Name, Age, Gender , City) 
 VALUES
 -- <Variable values>
 ('George','20', 'Male', 'London'),
 ('Emma','22', 'Female', 'Manchester'),
 ('Harry','15', 'Male', 'Cambridge'),
 ('Ava','17', 'Female', 'Manchester'),
 ('Olivia','25', 'Female', 'Manchester'),
 ('Thomas','33', 'Male', 'Cambridge');

SELECT * FROM information

Now, let's create a stored procedure with the code to select all entries from the database above.

CREATE PROCEDURE show_info
AS
BEGIN
    SELECT 
        Name, 
        Gender
    FROM 
        information
END;

#    
## Parameters in stored procedures

As mentioned earlier, we can also pass parameters in stored procedures. 

Consider an example of a stored procedure with a single parameter.

CREATE PROCEDURE showFemale @gender nvarchar(30)
AS
SELECT * FROM information WHERE Gender= @gender
GO;

The output of the code above will be as follows. 

| Name | Age | Gender | City |
| - | - | - | - |
| Emma | 22 | Female |Manchester |
| Ava | 17 | Female| Manchester |
| Olivia | 25 | Female | Manchester |

We can also create stored procedures with multiple parameters, as shown below.


CREATE PROCEDURE filter @gender nvarchar(30) @age nvarchar(10)
AS
SELECT * FROM information WHERE Gender= @gender AND Age >= @age
GO;

The code above will display all the male entries with an age greater than or equal to 22.

What are stored procedures in SQL?

Stored procedures are reusable, parameterized SQL codes stored for repeated use to manage databases.

Name	Gender
George	Male
Emma	Female
Harry	Male
Ava	Female
Olivia	Female
Thomas	Male

Name	Age	Gender	City
Emma	22	Female	Manchester
Ava	17	Female	Manchester
Olivia	25	Female	Manchester