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SQL Basics
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What is SQL?
• SQL stands for Structured Query Language .
• SQL lets you access and manipulate databases .
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What Can SQL do?
• Can execute queries against a database.
• Can retrieve data from a database. • Can insert records in a database.• Can update records in a database.
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What Can SQL do?
• Can delete records from a database.• Can create new databases. • Can create new tables in a database.
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SQL Statements
• Most of the actions you need to perform on a database are done with SQL statements.
• Ex: select all the records in the "Person" table. SELECT * FROM Person
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Keep in Mind That...
• SQL is not case sensitive
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SQL
SQL
Transaction control•Commit •Rollback
DML•Select•Insert•Update•Delete
DDL•Create•Alter•Drop
DCL•Grant•Revoke
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Is used to change structure of databaseIs used to change structure of database Create TableCreate Table Drop TableDrop Table Alter TableAlter Table
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Data Definition Language (DDL)
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Create Table
• The Create table statement is used to create a table in a database and to add constraints .– Constraints:
• NOT NULL • UNIQUE • PRIMARY KEY • FOREIGN KEY • CHECK • DEFAULT
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The data types
• Ex: some popular data types used in creating fields.
Data Type Name INT
DOUBLE
CHAR(n)
VARCHAR(n)
DATE
TIME
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CREATE TABLE person( id int,
name varchar(50) not null,
email varchar(50),
age int default 18,
Dept_ID int,
primary key(id),
check(age>17),
unique(email),
foreign key (Dept_ID) REFERENCES Department(Dept_ID))
Create Table Example
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Drop Table
• Used to remove a relation (base table) and its definition
• The relation can no longer be used in queries, updates, or any other commands since its description no longer exists
• Example:DROP TABLE DEPENDENT;
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Alter Table
• Used to modify the table design like add a column, modify a column or delete a column.
• Examples:ALTER TABLE EMPLOYEE ADD JOB VARCHAR(12)
ALTER TABLE EMPLOYEE MODIFY COLUMN JOB VARCHAR(50)
ALTER TABLE EMPLOYEE DROP COLUMN JOB
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Used to manipulate database dataUsed to manipulate database data
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Data Manipulation Language (DML)
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SELECTSELECTo Extracts data from a database
INSERT INTOINSERT INTOo Inserts new data into a database
UPDATEUPDATEo Updates data in a database
DELETEDELETEo Deletes data from a database
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Data Manipulation Language (DML)
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INSERT INTO Statement
• First form: It doesn't specify the column names where the data will be inserted, only their values.
– The previous form the attribute values should be listed in the same order as the attributes were specified in table.
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INSERT INTO Employee VALUES (4,'Ahmed', ‘Ali', 112233, '1965-01-01 ', '15 Ali fahmy St.Giza‘, ‘M’,1300,223344,10)
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INSERT INTO Statement, (cont.)
• Second form: It specifies both the column names and the values to be inserted
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INSERT INTO Employee (SSN, Lname, fname)
VALUES (5, ‘Ahmed', ‘Ali')
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• To insert a new row into table with identity value, we will not have to specify a value for the identity column (a unique value will be added automatically):
insert into Department values('DP2','56733')
insert into Department(Dname,MGRSSN) values('DP2','56733')
INSERT INTO Statement, (cont.)
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UPDATE Statement
• The UPDATE statement is used to update existing records in a table.
• SQL Syntax– UPDATE table_nameSET column1=value, column2=value2,...WHERE some_column=some_value
• Note: The WHERE clause specifies which record or records that should be updated. If you omit the WHERE clause, all records will be updated!
UPDATE Person SET Address='18 Abaas El 3akaad
St. Nasr City.Cairo', City='Cairo' WHERE Lname=‘Amr' AND Fname='Ali'
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DELETE Statement
• The DELETE statement is used to delete rows in a table.
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delete from Employee
delete from Employee
where Lname='Brown’
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SELECT Statement
• Basic form of the SQL SELECT statement is called a mapping or a SELECT-FROM-WHERE blockSELECT <attribute list>FROM <table list>WHERE <condition>– <attribute list> is a list of attribute names whose
values are to be retrieved by the query– <table list> is a list of the relation names required
to process the query– <condition> is a conditional (Boolean) expression
that identifies the tuples to be retrieved by the query
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Or:
SELECT Statement Examples
SELECT Lname,Fname FROM Person
SELECT Person.Lname, Person.Fname FROM Person
SELECT * FROM Person WHERE City='Sandnes'
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LIKE Operator ExampleSELECT * FROM Person WHERE City LIKE 's%'
SELECT * FROM Person WHERE City LIKE '%s'
SELECT * FROM Person WHERE City LIKE '_andnes'
Used to represent one character
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SQL AND & OR Operators• AND operator displays records when all
conditions are true.
• OR operator displays records when any condition is true.
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SQL AND & OR Operators Example
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IN Operator Example
• Retrieve data of all employees whose social security numbers number is 112233, or 512463.– Query : SELECT * FROM Employee WHERE SSN IN
(112233,512463)
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IN Operator Example
• Retrieve data of all employees whose social security numbers number is not 112233, or 512463.– Query :
SELECT * FROM Employee WHERE SSN not IN (112233,512463)
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The BETWEEN Operator
• The BETWEEN operator is used in a WHERE clause to select a range of data between two values.
• Retrieve the employees with salary between 1000 and 2000 – Query : SELECT * FROM EMPLOYEE WHERE SALARY BETWEEN 1000 AND 2000
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NULLS IN SQL QUERIES
• SQL allows queries that check if a value is NULL.• SQL uses IS or IS NOT to compare Nulls.• Retrieve the names of all employees who do not
have supervisors.– Query :
SELECT FNAME, LNAMEFROM EMPLOYEEWHERE SUPERSSN IS NULL
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DISTINCT Keyword
• The keyword DISTINCT is used to eliminate duplicate tuples in a query result.
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Thank YouThank You