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SQL. STRUCTURED QUERY LANGUAGE. Relationship. E-R-DIAGRAM :. Composite attribute. N. Work for. L NAME. M. location. name. F name. Department. NAME. Multivalued attribute. Entity. ssn. number. 1. No.of employee. Mgr. 1. EMPLOYEE. Key attribute. Employer. - PowerPoint PPT Presentation
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E-R-DIAGRAM :
L NAME
NAME
EMPLOYEE
Super vision
Work for
name
Department
Mgr No.of employee
number
location
Dependent of
dependent Relationship
name
F name
ssn
Composite attribute
Relationship
Multivalued attributeEntity
Key attribute
Derived attribute
Identifying weak relationship
Employer
N 1
1
1
M
N
CONSTRAINTS These are the restriction or condition that are used on the column of the table to preserve the data
correctness .
Constraints type are following :
1. Unique
2. Check
3. Not null
4. Primary key
5. Foreign key
oNot null This ensure that at least some values should be present for an attribute
Can have more than one not null on a table .
Null : Null is neither zero or blank space .
It is used to represent empty .
Ex : Name cannot be left blank/null in table .
Unique :
o It checks for duplicate values a unique .
o A unique column can have multiple null value .
Ex : employee id / mobile / mail id .
Check :
Check is used for enforcing some additional condition with respect to business
Requirement .
Ex : Sal > 3000 , Age >14 .
Primary key :
o It is used for identifying a record uniquely in a table . It is the combination of “ Not null “ and “ Unique” constraints
o You can have only one primary key is allowed per table .
Ex :
Employee id or mobile / mail id can be used as primary key .
Note :….
Candidate key : Eligible to become a primary key
Primary key : Unique and Not null .
Alternate key : Eligible to become a primary key but not chosen as primary key.
when “p k” is created out of more than one column then
it is called as composite primary key.
C k = P k + A k
A k = C k – P k
Foreign key : It is referential integrity constraints which created the relationship
between the table . To create a foreign key in a child table , Master
table should have a primary key on the common column .
composite primary key in master table is used as composite foreign key in child table .Foreign key can take both null and duplicate value .There can be more than one foreign key in
Table .
child table Master tableF.K P.K
RDBMS : Relational database management system2-dimensional architecture
If client is directly connected to database then it is 2-tier
Database management system (DBMS) .
Databaseserverclient
SQL STATEMENT :One language with 5 sub languages : -
1. DQL (Data query language )
2. DML (Data manipulation language)
3. DDL (Data definition language)
4. TCL/DTL (Data transaction language / Transaction control language)
5. DCL (Data control language)
Sub language Action performed
DQL (Data query language)
1. Select
DML (Data manipulation language)
1. Insert2. Update3. Delete
DDL (Data definition language)
1. Create2. Alter3. Drop
4. Rename5. Truncate
DTL (Data transaction language)
1. Commit2. Rollback
3. Save point
DCL (Data control language)
1. Grant2. Revoke
Select (DQL) : Capabilities of SQL SELECT statement :
Projection : selecting column Selection : selecting rows
tab 1 tab 2
Join
Basic select statement :SELECT * |{ [ DISTINCT ] Column / Expression [ alias ]….} |FROM Table ;
Ex : select empno ,ename ,sal from emp ;
ENAME EMPNO SAL
---------- ---------- ----------
SMITH 7369 800
ALLEN 7499 1600
WARD 7521 1250
JONES 7566 2975
MARTIN 7654 1250
BLAKE 7698 2850
CLARK 7782 2450
SCOTT 7788 3000
KING 7839 5000
9 rows selected.
SELECT identifies what column.
FROM identifies which table.
Writing SQL Statement :o SQL Statement are not case sensitive .
o SQL Statement can be one or more lines .
o Keyword can not be abbreviated or split across lines .
o Clauses are usually placed on separate lines .
o / (forward slash) is used in the place of semi colon but if it is in the next line
o SQL also use arithematic operations .
like :
select ename,sal,sal+500
from emp ;
select ename ,sal ,sal *12
from emp ;
Arithmetic expression :Create expression with number and date data by using arithmetic operators .
Question :
Calculate a salary increase of 300 for all employees and display
Both old and new salary ?
Answer :
Operator Description
+ Add
- Subtract
* Multiply
/ Divide
Operator Precedence :
Multiplication and Division take priority before addition and subtraction
Operator of the same priority are evaluated from left to right . Parentheses (Brackets) are used to force prioritized evaluation
and to clarify statements . If we are doing any arithmetic operation with null then it is
always null . If we are adding two column and value of one column is null
then the final value is null .
* , / ,+ , -
The create table statement :
You must have : CREATE TABLE privilege
You specify :
Table name column name ,column data type and column size and constraints .
CREATE TABLE [ schema.] table (column data type [DEFAULT Expression][;……] ) ;
Creating tables
Create table dept 1 ( dept no number (2), dname varchar2 (14), loc varchar2 (13));
Create table emp 1(emp no number (4) primary key,Ename varchar2 (10) not null,Age number (10) check (age > 14),Mobile number (10) unique,Dept no number (2) reference dept (dept no));
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