Structure query language, database course

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Structured Query Language
prepare by:Fikirte G
Chapter : 5

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Structure Query Language(SQL) commands
• SQL is a computer language for storing,
manipulating and retrieving data stored in a relational
database.
• SQL is the standard language for Relational Database
System.
• It has statements for data definitions, queries, and
updates
• The main SQL command for data definition is the
CREATE statement,

Why SQL?
• SQL is widely popular because it offers the following
advantages:
✓ Allows users to access data in the relational database management
systems.
✓ Allows users to describe the data.
✓ Allows users to define the data in a database and manipulate that data.
✓ Allows to embed within other languages using SQL modules, libraries
& pre-compilers.
✓ Allows users to create and drop databases and tables.
3

Cont’d
• SQL commands can be divided into the following three
functional groups:-
▪ Data Definition Language (DDL) - used to define the
schema (structure) of the database.
➢ DATABASE
✓ CREATE DATABSE
✓ DROP DATABASE
▪ Table
✓ CREATE TABLE
✓ ALTER TABLE
✓ DROP TABLE
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5
Data Manipulation Language (DML) - used to retrieve and
update data from the database.
SELECT
INSERT
UPDATE
DELETE
Data Control Language (DCL) - used to manipulate the
processing of data.

SQL DATA DEFINITION LANGUEGE (DDL)
• The SQL CREATE DATABASE statement is used to create a new SQL database.
Syntax
The basic syntax of this CREATE DATABASE statement is as follows −
CREATE DATABASE DatabaseName;
Example : CREATE DATABASE Employee
Syntax
The basic syntax of DROP DATABASE statement is as follows
DROP DATABASE DatabaseName;
Example : DROP DATABASE Employee
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Cont’d
• The SQL USE statement is used to select any existing
database in the SQL schema.
Syntax
• The basic syntax of the USE statement is as shown below −
Example USE DatabaseName
USE Employee;
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8
Cont’d
TABLES
Creating a basic table involves naming the table and defining its columns
and each column's data type.
• The SQL CREATE TABLE statement is used to create a new table.
Syntax
• The basic syntax of the CREATE TABLE statement is as follows −
CREATE TABLE table_name( column1 datatype, column2
datatype, column3 datatype, ..... columnN datatype, PRIMARY
KEY( one or more columns ) );

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Example: Define the student table:
CREATE TABLE STUDENT
( SID int,
FNAME varchar(18),gender varchar(18),age int
PRIMARY KEY (SID));
Cont’d

Cont’
➢The SQL DROP TABLE statement is used to remove a
table
Syntax
The basic syntax of this DROP TABLE statement is as follows
DROP TABLE table_name;
Example
DROP TABLE employee
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SQL DATA MANIPULATION LANGUAGE (DML)
⚫ The DML component of SQL is the part that is used to query
and update the tables
⚫ The most commonly used DML statement is the SELECT.
⚫ It combines a range of functionality into one complex
command.
⚫ Insert
⚫ Select
⚫ Update
⚫ Delete

INSERT
• The SQL INSERT INTO Statement is used to add new rows of data
to a table in the database.
Syntax
• There are two basic syntaxes of the INSERT INTO statement which
are shown below.
INSERT INTO TABLE_NAME (column1, column2,
column3,...columnN) VALUES (value1, value2, value3,...valueN);
INSERT INTO TABLE_NAME VALUES
(value1,value2,value3,...valueN);
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Cont’d
Example
• The following statements would create two records
in the employee table.
• INSERT INTO Employee (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (1, ‘Abebe', 32, ‘yeka', 2000.00 );
• INSERT INTO Employee (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (2, ‘Mohamed', 25, ‘Mixico', 3500.00 );
• create a record second syntax as shown below.
• INSERT INTO Employee VALUES (3, ‘Saron', 24,
‘4 kilo', 10000.00 );
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DELETE
• The DELETE statement removes tuples from a
relation.
• It includes a WHERE clause, similar to that used in
an SQL query, to select the tuples to be deleted.
• Tuples are explicitly deleted from only one table at a
time.
syntax
• DELETE FROM table name
WHERE condition
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UPDATE
• The UPDATE statement is used to modify attribute
values of one or more selected tuples.
• As in the DELETE statement, a WHERE clause in the
UPDATE command selects the tuples to be modified from a
single relation
• syntax
UPDATE table name
SET values
WHERE condition
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▪The SQL SELECT statement is used to fetch the data
from a database table which returns this data in the form of
a result table.
▪These result tables are called result-sets.
Syntax
▪The basic syntax of the SELECT statement is as follows:
SELECT column1, column2, column N
FROM table_name;
WHERE <condition>;
.
SELECT
SELECT

Cont’d
where
■ <column 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.
• In SQL, the basic logical comparison operators for
comparing attribute values with one another and with
literal constants are =, <, <=, >, >=, and <>.
17

Cont’d
• If you want to fetch all the fields available in the
field, then you can use the following syntax.
• SELECT * FROM table_name;
• The following code is an example, which would
fetch the ID, Name and Salary fields of the
customers available in CUSTOMERS table.
• SELECT ID, NAME, SALARY FROM
CUSTOMERS;
18

Cont’d
Example
• Find Cid, FName and Salary fields from the
CUSTOMERS table, where the salary is greater
than 2500 −
SELECT Cid, FName, Salary FROM
CUSTOMERS WHERE Salary > 2500;
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GROUP BY
The SQL GROUP BY clause is used in collaboration with the
SELECT statement to arrange identical data into groups.
⚫ The GROUP BY clause is used to specify one or more
fields that are to be used for organizing tuples into groups.
⚫ Rows that have the same value(s) are grouped together.
⚫ The only fields that can be displayed are the ones used for
grouping and ones derived using column functions.
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Cont’d
Syntax
• The basic syntax of a GROUP BY clause is shown in the following
code block.
• The GROUP BY clause must follow the conditions in the WHERE
clause and must precede the ORDER BY clause if one is used.
• SELECT column1, column2
FROM table_name
WHERE [ conditions ]
GROUP BY column1, column2
ORDER BY column1, column2
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Cont’d
• If you want to know the total amount of the
salary on each customer, then the GROUP BY
query would be as follows.
SELECT NAME, SUM(SALARY)
FROM CUSTOMERS
GROUP BY NAME
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ORDER BY clause
• The SQL ORDER BY clause is used to sort the data in ascending or
descending order, based on one or more columns.
• Some databases sort the query results in an ascending order by default.
Syntax
• The basic syntax of the ORDER BY clause is as follows −
SELECT column-list FROM table_name
[WHERE condition]
[ORDER BY column1, column2, .. columnN] [ASC | DESC];
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Cont’d
• The following code block has an example, which would sort
the result in an ascending order by the NAME and the
SALARY −
SELECT * FROM CUSTOMERS
ORDER BY NAME, SALARY;
• The following code block has an example, which would sort
the result in the descending order by NAME.
SELECT * FROM CUSTOMERS
ORDER BY NAME DESC;
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Cont’d
⚫ You can select either ascending or descending sort for each named
column.
Example 1: List the FName and SID of all faculty members arranged
in alphabetical order.
SELECT SID, FNAME
FROM Student
ORDER BY FName;

HAVING Clause
• The HAVING Clause enables you to specify conditions that
filter which group results appear in the results.
• The WHERE clause places conditions on the selected
columns,
• whereas the HAVING clause places conditions on groups
created by the GROUP BY clause.
• The HAVING clause must follow the GROUP BY clause in
a query and must also precede the ORDER BY clause if
used.
26

Cont’d
Syntax
The following code block has the syntax of the SELECT
statement including the HAVING clause −
SELECT column1, column2
FROM table1, table2
WHERE [ conditions ]
GROUP BY column1, column2
HAVING [ conditions ]
ORDER BY column1, column2
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MORE COMPLEX SINGLE TABLE RETRIEVAL
⚫ The WHERE clause can be enhanced to be more selective.
⚫ Operators that can appear in WHERE conditions include:
= ,< ,> ,>= ,<=
IN
BETWEEN...AND...
LIKE
IS NULL
AND, OR, NOT

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COLUMN FUNCTIONS (AGGREGATE FUNCTIONS)
⚫ Aggregate functions allow you to calculate values based upon all
data in an attribute of a table.
⚫ The SQL aggregate functions are: Max, Min, Avg, Sum, Count
etc
⚫ Note:
⚫ AVG and SUM work only with numeric values and both exclude
NULL values from the calculations.
Example 1: How many students are there?
SELECT COUNT(*)
FROM STUDENT;

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MULTIPLE TABLE QUERIES
▪ A JOIN operation is performed when more than one table is
specified in the FROM clause.
▪ You would join two tables if you need information from both.
▪ You must specify the JOIN condition explicitly in SQL.
▪ This includes naming the columns in common and the
comparison operator.
▪ SQL specifies alias names in the FROM clause immediately
following the actual table

Join statement
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▪ A JOIN clause is used to combine rows from two or more tables ,
based on a related column between them.
▪ There are different types of the JOINs in SQL:
▪ INNER JOIN
▪ LEFT (OUTER) JOIN
▪ RIGHT (OUTER) JOIN
▪ FULL (OUTER) JOIN

Inner Join
• INNER JOIN: returns records that have matching
values in both tables
• Syntax
• SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;
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Left Join
• LEFT (OUTER) JOIN: returns all records from the left
table, and the matched records from the right table
• Syntax
FROM table1
LEFT JOIN table2
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RIGHT JOIN
• RIGHT (OUTER) JOIN: returns all records from
the right table, and the matched records from the left
table
• Syntax
FROM table1
RIGHT JOIN table2
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FULL OUTER JOIN
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▪ The FULL OUTER JOIN keyword returns all records when
there is a match in left (table1) or right (table2) table
▪ Syntax
SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table1.column_name = table2.column_name
WHERE condition;

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