SQL
- 2. Definition Of JOINS :- An SQL join clause combines records from two or more tables in a database. It creates a set that can be saved as a table or used as is. A JOIN is a means for combining fields from two tables by using values common to each.
- 3. Natural Join Self JOIN Equi Join Join S Outer Join
- 4. Natural Join - The NATURAL JOIN is a type of equi-join and is structured in such a way that, columns with same name of associate tables will appear once only. Eg - Select * FROM table1 NATURAL JOIN table2; EquiJoin - SQL EQUI JOIN performs a JOIN against equality or matching column(s) values of the associated tables. An equal sign (=) is used as comparison operator in the where clause to refer equality. Eg - Select column_list FROM table1, table2 WHERE table1.column_name =table2.column_name
- 5. Self Join - SELF JOIN is used to join a table to itself, as if the table were two tables, temporarily renaming at least one table in the SQL statement. Eg - SELECT a.column_name, b.column_name FROM table1 a, table1 b WHERE a.common_filed = b.common_field; Outer Join – Right Outer Join - Left Outer Join
- 6. Right Outer Join - The LEFT JOIN keyword returns all rows from the left table (table_name1), even if there are no matches in the right table (table_name2). Eg - SELECT column_name(s) FROM table_name1 LEFT JOIN table_name2 ON table_name1.column_name=table_name2.column_name Left Outer Join - The RIGHT JOIN keyword returns all the rows from the right table (table_name2), even if there are no matches in the left table (table_name1). Eg -SELECT column_name(s) FROM table_name1 RIGHT JOIN table_name2 ON table_name1.column_name=table_name2.column_name
- 7. A SQL nested query is a SELECT query that is nested inside a SELECT, UPDATE, INSERT, or DELETE SQL query. Here is a simple example of SQL nested query: Eg - SELECT Model FROM Product WHERE ManufacturerID IN (SELECT ManufacturerID FROM Manufacturer WHERE Manufacturer = 'Dell')
- 8. UNIONALL - Combines the results of two SELECT statements into one result set. SELECTCUST_NBR, NAME FROM CUSTOMER WHERE REGION_ID = 5 UNION ALL SELECT C.CUST_NBR, C.NAME FROM CUSTOMER C WHERE C.CUST_NBR IN (SELECT O.CUST_NBR FROM CUST_ORDER O, EMPLOYEE E WHERE O.SALES_EMP_ID = E.EMP_ID AND E.LNAME = 'MARTIN');
- 9. • UNION - Combines the results of two SELECT statements into one result set, and then eliminates any duplicate rows from that result set. Eg - SELECT CUST_NBR, NAME FROM CUSTOMER WHERE REGION_ID = 5 UNION SELECT C.CUST_NBR, C.NAME FROM CUSTOMER C WHERE C.CUST_NBR IN (SELECT O.CUST_NBR FROM CUST_ORDER O, EMPLOYEE E WHERE O.SALES_EMP_ID = E.EMP_ID AND E.LNAME = 'MARTIN');
- 10. MINUS - Takes the result set of one SELECT statement, and removes those rows that are also returned by a second SELECT statement. Eg - SELECT CUST_NBR, NAME FROM CUSTOMER WHERE REGION_ID = 5 MINUS SELECT C.CUST_NBR, C.NAME FROM CUSTOMER C WHERE C.CUST_NBR IN (SELECT O.CUST_NBR FROM CUST_ORDER O, EMPLOYEE E WHERE O.SALES_EMP_ID = E.EMP_ID AND E.LNAME = 'MARTIN');
- 11. INTERSECT - Returns only those rows that are returned by each of two SELECT statements. Eg - SELECT CUST_NBR, NAME FROM CUSTOMER WHERE REGION_ID = 5 INTERSECT SELECT C.CUST_NBR, C.NAME FROM CUSTOMER C WHERE C.CUST_NBR IN (SELECT O.CUST_NBR FROM CUST_ORDER O, EMPLOYEE E WHERE O.SALES_EMP_ID = E.EMP_ID AND E.LNAME = 'MARTIN');