Introduction To Structured Query Language (SQL)

SQL SQL is a standard language for accessing databases. Our SQL tutorial will teach you how to use SQL to access and manipulate data in: MS Access SQL Server database systems.

What is SQL? SQL stands for Structured Query Language SQL lets you access and manipulate databases SQL is an ANSI (American National Standards Institute) standard

What Can SQL do? SQL can execute queries against a database SQL can retrieve data from a database SQL can insert records in a database SQL can update records in a database SQL can delete records from a database SQL can create new databases SQL can create new tables in a database SQL can create stored procedures in a database SQL can create views in a database SQL can set permissions on tables, procedures, and views

Some of The Most Important SQL Commands SELECT - extracts data from a database UPDATE - updates data in a database DELETE - deletes data from a database INSERT INTO - inserts new data into a database CREATE DATABASE - creates a new database ALTER DATABASE - modifies a database CREATE TABLE - creates a new table ALTER TABLE - modifies a table DROP TABLE - deletes a table CREATE INDEX - creates an index (search key) DROP INDEX - deletes an index

Student

SELECT Statements In this tutorial we will use the well-known sample database (included in MS Access and MS SQL Server). The following SQL statement selects all the records in the table: Statement: SELECT * FROM Table; E.g.: SELECT * FROM Student;

SELECT Statements SELECT column_name,column_name FROM table_name; Select id, Firstname, age From Student;

SQL SELECT DISTINCT Statement The SELECT DISTINCT statement is used to return only distinct (different) values. SELECT DISTINCT column_name,column_name FROM table_name;

SQL WHERE Clause The WHERE clause is used to filter records. SELECT * FROM Student WHERE Field_Name ="Text Value"; SELECT * FROM Student WHERE Field_Name =Numeric Value;

Operators in The WHERE Clause Description = Equal <> Not equal. Note: In some versions of SQL this operator may be written as != > Greater than < Less than >= Greater than or equal <= Less than or equal BETWEEN Between an inclusive range LIKE Search for a pattern IN To specify multiple possible values for a column

AND & OR Operators The AND & OR operators are used to filter records based on more than one condition. SELECT * FROM Student WHERE City =Nizwa" AND Age < 30; SELECT * FROM Student WHERE City =Nizwa" OR Age < 30; SELECT * FROM Student WHERE City=Nizwa" AND (lastname= "said" OR firstname="ali");

Operators in The WHERE Clause The BETWEEN operator selects values within a range. The values can be numbers, text, or dates. SELECT column_name(s) FROM table_name WHERE column_name BETWEEN value1 AND value2; Not Between used to NOT Include SELECT Firstname, Lastname, city, age FROM student WHERE city NOT BETWEEN "Muscat" AND "Izki";

IN Operator The IN operator allows you to specify multiple values in a WHERE clause. SELECT column_name(s) FROM table_name WHERE column_name IN (value1,value2,...);

LIKE Operator The LIKE operator is used to search for a specified pattern in a column. SELECT * FROM Student WHERE City LIKE "s*";

ORDER BY Keyword The ORDER BY keyword is used to sort the result-set. SELECT * FROM student ORDER BY city; SELECT * FROM student ORDER BY city ASC /DESC; SELECT * FROM student ORDER BY city, firstname; SELECT * FROM student ORDER BY city ASC, lastname DESC;

INSERT INTO Statement The INSERT INTO statement is used to insert new records in a table. INSERT INTO Student(FirstName, LastName, City, age, Mob) VALUES (‘Nour',Elshaiekh',Halfa',42, 5654566);

UPDATE Statement The UPDATE statement is used to update records in a table. UPDATE Student SET LastName= “Mussab”, City= “Suhar” WHERE FirstName= “Ali”;

Delete Statement The DELETE statement is used to delete records in a table. DELETE FROM Student WHERE FirstName="Ali" AND LastName="Said" ;

SELECT TOP Clause The SELECT TOP clause is used to specify the number of records to return. SELECT TOP 2 * FROM Student;

SELECT TOP Clause SQL statement selects the first ?% of the records from the table: SELECT TOP 20 PERCENT * FROM Student;

SQL JOIN An SQL JOIN clause is used to combine rows from two or more tables, based on a common field between them. SELECT abs.name, Student.FirstName, ab.age FROM student INNER JOIN ab ON ab.Name=student.FirstName;

SQL Aliases SQL aliases are used to give a database table, or a column in a table, a temporary name. Basically aliases are created to make column names more readable. SELECT FirstName AS CEMIS FROM Student;

The SQL UNION Operator The UNION operator is used to combine the result-set of two or more SELECT statements SELECT FirstName FROM Student UNION SELECT FirstName FROM ab; SELECT City FROM Student SELECT FirstName From ab ORDER BY City;