SQL THOERY SHORT NOTE PART 1
DATA: IS COLLECTION/GROUP OF FACTS LIKE EMPNO,ENAME,SAL
FIGURES: EMPPHOTO,
RESULTS: TOTSAL(SAL+COMM).
DATABASE: STORAGE AREA,COLLECTION,GROUP OF DATA.
AS SOFTWARE.
DBMS: DATABASE MANAGEMENT SYSTEM.
1.INTERFACE: AN EDITOR OR A PLACE TO TYPE THE COMMANDS TO PROCESS DATA.
EX: ORACLE WE HAVE SQLPLUS, EDITOR TO TYPE THE COMMANDS TO PROCESS DATA.
2.QUERY PROCESSOR: A COMPILER TO COMPILE THE COMMAND GIVEN BY THE USER.
SQL: IS NOT CASE SENSITIVE.
EX:
select * from dept;
3.DATABASE: STORAGE AREA OF STORING YOUR TABLES.
4.FILE SYSTEM: THE HARD WHERE THE DATA IS STORED.
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DIFFERENT DATA MODELS: HOW THE DATA STORED IN THE OLD DAYS.
1.HIERARCHY MODEL: IN THIS MODEL THE DATA WAS STORED IN FORM OF FILES.
2.THE FILES COULD HAVE RELATIONSHIP LIKE PARENT AND CHILD.
EX: EVERY EMPLOYEE WILL WORK IN A DEPT.
DEPT:(MASTER/PARENT)
10 AC BDC
EMP:(DETAIL/CHILD).
101 JACK 5000 10
SCANNING OF DATA FROM PARENT TO CHILD FROM TOP TO BOTTOM BECOMES FASTER.
DIS: WE CANNOT HAVE ONE CHILD HAVE MULTIPLE PARAENTS.
MEMBERS:
MID MNAME
101 RAJ
1.MOVIES:
MOVID MOVNAME
1 TITANIC
RENTAL:
MID MOVID ORDATE RET DATE
101 1 12 AUG 15 AUG
2.NETWORK MODEL:
DATA WAS STORED IN FORM OF FILES.
THE RELATIONSHIP WAS STORED IN FORM OF NODES.
WE CAN HAVE ONE CHILD HAVING MORE THAN ONE PARENT.
DIS: VERY COMPLEX. AND IF WE DROP
ONE RELATIONSHIP THEN WE HAVE RECREATE THE ENTIRE MODEL ONCE WHICH IS DIFFICULT.
EX: DBASE,FOXPRO
3.RDBMS(RELATIONAL MODEL):
THE DATA IS NOT STORED IN FORM FILES BUT IN FORM OF TABLES.
IN THE OLD MODELS THE DATA WAS IN FORM OF FILES.
SO IF WE HAVE 100 STRUCTURES THEN WE WILL HAVE 100 FILES IN THE OS.
IN THOSE HOW MANY MAX FILES CAN WE HAVE??SO THE SIZE OF THE DATA BASES THOSE
DAYS WERE VERY SMALL. THEY COULD SUPPORT HARDLY GB OF DB
ADV: WE CAN HAVE BIG STORAGE AREA LIKE TB,PB.
EX: ORACLE,SYBASE,DB2,SQLSERVER,...
NOTE: IN ORACLE WE CAN HAVE ONE SIGLE FILE TO SIZE OF 128TB.
4.ORDBMS: WE CAN CREATE OBJECTS OR WE CAN CREATE INSTANCES.
EMP:
EMPNO ENAME FNO STNO CITY
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CUSTOMER:
CID CNAME FNO STNO CITY
-------------------------------------
ADDRESS
FNO STNO CITY
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EMP:
EMPNO ENAME ADDR ADDRESS
CUSTOMER:
CID CNAME ADDR ADDRESS
NOTE: ORACLE IS ALSO FOLLOWING THIS ORDBMS MODEL.
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RELATIONSHIP:
TABLE: IS A RELATION
RELATION: ASSOCIATION BETWEEN TABLES.
COLUMN: IS AN ATTRIBUTE.
TUPLE: ROW.
CARDINALITY: NUMBER OF ROWS.
DEGREE: NUMBER OF COLUMNS.
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PRIMARY KEY: NOT NULL AND UNIQUE.
FOREIGN KEY: USED TO BUILD RELATIONSHIP WITH THE PK.
ALTERATE KEY: SINCE IN A TABLE WE CAN HAVE ONLY ONE PK, WE CAN MAKE OTHER COLUMNS
AS A INDIRECT PK USING THE ALTERATE KEY(NOT NULL+UNIQUE)
CANDIDATE KEY: NOT NULL AND UNIQUE
1.PK: ONLY ONE PK IN A TABLE.
2.AKEY:
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