SQL Tutorial : DRL / DQL - JOINS

SQL Tutorial : DRL / DQL - JOINS

Let's learn about next topic: JOINS

JOINS:

- FETCHING DATA FROM MULTIPLE TABLES BY COMPARING COLUMNS

BETWEEN THE TABLES

ORACLE JOINS :

 1. EQUI JOIN

 2. NON-EQUI JOIN
 3. SELF JOIN
 4. OUTER JOIN

ANSI SQL JOINS :

 1. CROSS JOIN

 2. NATURAL JOIN

3. USING CLAUSE

 4. ON CLAUSE

 5. LEFT OUTER JOIN

6. RIGHT OUTER JOIN

7. FULL OUTER JOIN

SELECT LAST_NAME,SALARY ,DEPARTMENT_NAME

FROM EMPLOYEES,DEPARTMENTS

 

CARTESIAN PRODUCT :

- CROSS PRODUCT OF TWO TABLES

1.WHEN JOIN CONDITION IS OMITTED

2. WHEN JOIN CONDITION IS INVALID

- SELECT LAST_NAME,SALARY ,DEPARTMENT_NAME

 FROM EMPLOYEES,DEPARTMENTS

WHERE DEPARTMENT_ID =DEPARTMENT_ID

Point to note:
- QUALIFYING IS THE PROCESS OF PREFIXING THE TABLE NAME OR
TABLE ALIASES BEFORE THE COLUMN NAME

1.AVOIDS CONFUSION

2.IMPROVES THE SEARCH