Lecture Database management systems Chapter 8 SQL

SQL

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Introduction
 SQL commands can be classified in to three types:
 Data Definition Language commands (DDL)
 Data Manipulation Language commands (DML)
 Data Control Language commands (DCL)

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Domain types
 Numeric:
 int. Integer (a finite subset of the integers that is
machine-dependent).
 smallint.
Small integer (a machine-dependent
subset of the integer domain type).
 numeric(p,d).
Fixed point number, with userspecified precision of p digits, with n digits to the
right of decimal point.
 real, double precision. Floating point and doubleprecision floating point numbers, with machinedependent precision.
 float(n). Floating point number, with user-specified
precision of at least n digits.

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Domain types
 String:
 char(n). Fixed length character string, with
user-specified length n.
 varchar(n).
Variable length character
strings, with user-specified maximum length n
 nvarchar(n). similar to varchar, except it
uses Unicode and therefore doubles the
amount of space required to store the data.
 Text: holds data that is longer than 8,000
characters
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Domain types
 Datetime:
 datetime. store not only a date, but also a
time alongside it.
 smalldatetime.

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Create Table Construct
 An SQL relation is defined using the create table command:

create table r
(A1 D1, A2 D2, ..., An Dn,
(integrity-constraint1),
...,
(integrity-constraintk))
 r is the name of the relation
 each Ai is an attribute name in the schema of relation r
 Di is the data type of values in the domain of attribute Ai

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Create Table Construct
 department (dept_no, dept_name, location)
 Primary key: dept_no
 Candidate key: dept_name

 CREATE TABLE department
(
dept_no char(3) primary key,
dept_name varchar(36) unique not null,
location varchar(20)

)
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Integrity Constraints
 Constraints
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Null
Not null
Unique
Primary key
References (Foreign key)
Check
Default
On delete cascade
On update cascade
On delete set null

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Delete table
 Delete the whole table (include all data) in
database.
 DROP TABLE TableName
 Ex:
 DROP TABLE DEPARTMENT

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Truncate table
 The TRUNCATE TABLE command removes
all the rows from the table. The truncate
table also releases the storage space used
by the table.
 The syntax of TRUNCATE command is:
 TRUNCATE TABLE tablename

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Alias
 Tables listed in the FROM clause can be given an

alternative name
 An alias is created by:
 Typing the name of the table
 Pressing the space bar
 Typing the name of the alias

 One reason for using an alias is simplicity

 A second reason for using an alias is that it is needed
when joining a table to itself, called a self-join.

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Data Manipulation Language


Adding a New Row to the Table

INSERT INTO tablename
VALUES ('value1', 'value2',. . . ,'valuen')



Updating the Data in the Table

UPDATE table name
SET attribute value=new value

WHERE condition;

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Deleting Row from the Table

DELETE FROM table name
WHERE condition;

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INSERT statement
 Adds one or more new rows to a table or
a view.
 Example:
 Insert into department
values('MT','Mathematics','E2')
 Insert into department values(‘CSE',‘Computer
Science & Engineering','E2')
 Insert into employee values
('111111',‘Anna',‘Smith','MT','0122916425')
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UPDATE statement

 Changes existing data in a table or view.
 Example:
update department
set location='H1'
where dept_no=‘CSE'


DELETE statement
 Removes rows from a table or view.
 Example:
Delete from Employee
Where emp_fname='Anna '


SELECT Statement
 Used for queries on single or multiple tables

 SELECT
 List the columns (and expressions) that should be returned from
the query
 FROM
 Indicate the table(s) or view(s) from which data will be obtained
 WHERE
 Indicate the conditions under which a row will be included in the
result
 GROUP BY
 Indicate categorization of results
 HAVING
 Indicate the conditions under which a category (group) will be
included

 ORDER BY
 Sorts the result according to specified criteria


Operators
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Comparison operators (=, <, <=, <>, and so on)
String comparisons (LIKE, NOT LIKE)
Logical operators (AND, OR, NOT)
Ranges (BETWEEN and NOT BETWEEN)
Lists of values (IN and NOT IN)
Unknown Values (IS NULL and IS NOT NULL)
Exists in Subquery (EXISTS and NOT EXISTS)
Use DISTINCT to eliminate duplicates
[ TOP (expression) [PERCENT] [ WITH TIES ] ]

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SELECT statement


The SQL syntax to see all the columns of the table is:
SELECT * FROM table name

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Syntax of SELECTION Operation:
SELECT * FROM table name
WHERE condition;

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Syntax of PROJECTION Operation
SELECT column name1, column name2, Column name N
FROM table name



Syntax for SELECTION and PROJECTION
SELECT column name1, column name 2. .... column nameN
FROM table name
WHERE condition;

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SELECT statement
Maths

- AVG()
- MIN()
- MAX()
- SUM()
- COUNT()
- SQUARE()
- SQRT()
- ROUND()

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String

- ASCII()
- CHAR()
- UPPER()
- LOWER()
- LEN()
- LTRIM()
- RTRIM()
- LEFT()
- RIGHT()

Time

- GETDATE()
DATEPART(YY,getda

te())
- DATEDIFF(X,Y,Z)
DAY(),MONTH(),YE
AR()

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SELECT data


SELECT * FROM DANHMUCSACH

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SELECT data
 SELECT *
FROM DANHMUCSACH
WHERE MANHOM = 'N001'

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SELECT - COUNT
 COUNT (*) Function:

 return the number of rows of the relation.
Command will take NULL values into account.

 COUNT (DISTINCT attribute_name):
 Return the number of Rows of the relation, by
eliminating duplicate values.


SELECT - COUNT
 SELECT COUNT(*) TONGSOSACH
FROM DANHMUCSACH
WHERE MANHOM = 'n001'


MAX, MIN, AVG, and SUM
 MAX Command

SELECT MAX (attribute name)
FROM table name;

 MIN Command

SELECT MIN (attribute name)
FROM table name;

 AVG Command

SELECT AVG (attribute name)
FROM table name;

 SUM Command


SELECT - GROUP BY
 The GROUP BY clause is used to group
rows to compute group-statistics.
 The syntax of GROUP BY command is:
SELECT attribute name, aggregate function
FROM table name
GROUP BY attribute name;