RDBMS Using Oracle. Lecture Week 7 Introduction to Oracle 9i SQL Last Lecture. kamran.munir@gmail.com. Joining Tables

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1 RDBMS Using Oracle Lecture Week 7 Introduction to Oracle 9i SQL Last Lecture Joining Tables Multiple Table Queries Simple Joins Complex Joins Cartesian Joins Outer Joins Multi table Joins Other Multiple Table Queries

2 The tables being joined are listed in the FROM clause. The join is performed in the WHERE clause. Several operators can be used to join tables, such as =, <, >, <>, <=, >=,!=, BETWEEN, LIKE, and NOT; they can all be used to join tables. However, the most common operator is the equal symbol. Simple Joins This most common join is Simple Join that is joining two tables with equality operator, it is an equality join also known as equijoin. EQUIJOIN,, also referred to as an INNER JOIN. The EQUIJOIN joins two tables with a common column in which each is usually the primary key.

3 The syntax for an EQUIJOIN is SELECT TABLE1.COLUMN1, TABLE2.COLUMN2...FROM TABLE1, TABLE2 [, TABLE3 ] WHERE TABLE1.COLUMN_NAME = TABLE2.COLUMN_NAME [AND TABLE1.COLUMN_NAME = TABLE3.COLUMN_NAME ] Example: Select emp.empno, emp.ename, dept.dname from emp,dept Where emp.deptno = dept.deptno Another Example Select emp.*, dept.dname, dept.loc from emp,, dept Where emp.deptno = dept.deptno Remember that the asterisk (*) represents all columns of a table. Cross Join Select * from emp, dept (Provides All Combinations)

4 Complex Joins Apart from specifying joining condition, we can also write some other condition to limit rows selected. Such joins are known as complex joins Select emp.*, dept.dname, dept.loc from emp,, dept Where emp.deptno = dept.deptno and emp.job = MANAGER

5 Joins of Non-Equality NON-EQUIJOIN joins two or more tables based on a specified column value not equaling a specified column value in another table. The syntax for the NON-EQUIJOIN is FROM TABLE1, TABLE2 [, TABLE3 ] WHERE TABLE1.COLUMN_NAME!= TABLE2.COLUMN_NAME [ AND TABLE1.COLUMN_NAME!= TABLE2.COLUMN_NAME ] Non-Equi Join Row count Suppose only 6 rows exist in each table. For every record in table A, there is a corresponding record in table B. Because non-equality is to be tested in the join of the two tables, each row in the first table is paired with all rows from the second table, except for its own corresponding row. This means that each of the 6 rows are paired with 5 unrelated rows in the second table; 6 rows multiplied by 5 rows equals 30 rows total.

6 Natural Join NATURAL JOIN is nearly the same as the EQUIJOIN; however, the NATURAL JOIN differs from the EQUIJOIN by eliminating duplicate columns in the joining columns. There is also no need to specify join condition, This join is based on all columns with the same name and datatype in both tables. Select empno, ename, dname from emp NATURAL JOIN dept; Select * from emp NATURAL JOIN dept;

7 Joins - Explanation When you join two or more tables, a good idea is to precede the field names with the table names. This is not mandatory unless the same field name is found in more than one table. If you precede the field name with a table name, place a period between the two names. For example, tablename.fieldname. You must specify which fields are being joined. If you do not specify which fields are being joined, the result is what is commonly referred to as a "Cartesian join" in which all rows in the first table are joined with all rows in the second table.

8 Outer Joins An OUTER JOIN is used to return all rows that exist in one table, even though corresponding rows do not exist in the joined table. The (+) symbol is used to denote an OUTER JOIN in a query. The (+) is placed at the end of the table name in the WHERE clause. The table with the (+) should be the table that does not have matching rows. In many implementations, the OUTER JOIN is broken down into joins called LEFT OUTER JOIN, RIGHT OUTER JOIN, and FULL OUTER JOIN. The Oracle syntax is Outer Join FROM TABLE1, TABLE2 [, TABLE3 ] WHERE TABLE1.COLUMN_NAME[(+)] = TABLE2.COLUMN_NAME[(+)] [ AND TABLE1.COLUMN_NAME[(+)] = TABLE3.COLUMN_NAME[(+)]] To write a query that performs an outer join of tables A and B and returns all rows form A, apply the outerjoin operator (+) to all columns of B in the join condition. For all rows in A that have no matching rows in B, the query returns NULL values for the columns in B.

9 Outer Join The next example accomplishes the desired output through the use of an OUTER JOIN. Oracle's syntax is used for the OUTER JOIN (right). SELECT P.PROD_DESC, O.QTY FROM PRODUCTS_TBL P, ORDERS_TBL O WHERE P.PROD_ID = O.PROD_ID(+); It will display all records of Products table and only matching records from Orders Table. Right Outer Join SELECT P.PROD_DESC, O.QTY FROM PRODUCTS_TBL P, ORDERS_TBL O WHERE P.PROD_ID (+) = O.PROD_ID; Note: IN KEYWORD RIGHT OUTER JOIN AND LEFT OUTER JOIN The word OUTER Is Optional. SELECT P.PROD_DESC, O.QTY FROM PRODUCTS_TBL P RIGHT OUTER JOIN ORDERS_TBL O on P.PROD_ID = O.PROD_ID; SELECT P.PROD_DESC, O.QTY FROM PRODUCTS_TBL P RIGHT join ORDERS_TBL O USING (PROD_ID( PROD_ID);

10 Left Outer Join SELECT P.PROD_DESC, O.QTY FROM PRODUCTS_TBL P, ORDERS_TBL O WHERE P.PROD_ID = O.PROD_ID(+); SELECT P.PROD_DESC, O.QTY FROM PRODUCTS_TBL P LEFT OUTER JOIN ORDERS_TBL O on P.PROD_ID = O.PROD_ID; SELECT P.PROD_DESC, O.QTY FROM PRODUCTS_TBL P Left join ORDERS_TBL O USING (PROD_ID( PROD_ID);

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13 Self Join Self Joins The 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. The syntax is as follows. The following is an example: SELECT A.LAST_NAME, B.LAST_NAME, A.FIRST_NAME FROM EMPLOYEE_TBL A, EMPLOYEE_TBL B WHERE A.LAST_NAME = B.LAST_NAME; Multi table Joins Joining on Multiple Keys We may have a table that has a primary key that is comprised of more than one column. You may also have a foreign key in a table that consists of more than one column, which references the multiple column primary key.

14 Consider the following Oracle tables that are used here for examples only: SQL> desc prod Name Null? Type SERIAL_NUMBER NOT NULL NUMBER(10) VENDOR_NUMBER NOT NULL NUMBER(10) PRODUCT_NAME NOT NULL VARCHAR2(30) COST NOT NULL NUMBER(8,2) SQL> desc ord Name Null? Type ORD_NO NOT NULL NUMBER(10) PROD_NUMBER NOT NULL NUMBER(10) VENDOR_NUMBER NOT NULL NUMBER(10) QUANTITY NOT NULL NUMBER(5) ORD_DATE NOT NULL DATE The primary key in PROD is the combination of the columns SERIAL_NUMBER and VENDOR_NUMBER. The foreign key in ORD is also the combination of the columns SERIAL_NUMBER and VENDOR_NUMBER. When selecting data from both tables (PROD and ORD), the join operation may appear as follows: SELECT P.PRODUCT_NAME, O.ORD_DATE, O.QUANTITYFROM PROD P, ORD O WHERE P.SERIAL_NUMBER = O.SERIAL_NUMBER AND P.VENDOR_NUMBER = O.VENDOR_NUMBER;

15 Creating VIEWS Improve Security Through Views A view is often referred to as a virtual table allows a user to see a customized selection of one or more tables is stored as an SQL query, which is executed whenever the view is used reflects the current state of the database can be treated as another table (with special restrictions on modifying the data within the view)

16 A view is created using the create view command is displayed using a normal select command can be referred to by a select, insert, update or delete command is dropped using the drop view command 3 create view dept30_emps as view name (select empno, ename, job, mgr from emp where deptno = 30); query select * from dept30_emps; 4

17 emp table dept30_emps view 5 view name create view annual_costs as (select empno, ename, comm, sal*12 from emp); annual_sal query 6

18 emp table annual_costs view 7 All columns produced using expressions such as sal*12 must be given aliases: create view annual_costs as (select empno, ename, comm, sal*12 annual_sal from emp); 8

19 Any other columns may also be given aliases: create view annual_costs as (select empno, ename name, comm commission, sal*12 annual_sal from emp); 9 10

20 All the columns may be given aliases as follows: create view annual_costs (employee, name, commission, annual_sal) as (select empno, ename, comm, sal*12 from emp); 11 12

21 The order by clause may not be used in creating a view as the order of rows of a table or view is not defined. After the view is created, a query can be written to display the view in the required order: select * from annual_costs commission, annual_sal; order by 13 14

22 Views are often used to collect summary data, e.g. create view dept_size (department, no_of_emps) as (select dname, count(empno) from dept, emp Where dept.deptno = emp.deptno (+) group by dname); 15 16

23 A view provides an additional level of security different groups of users have different database privileges a view can be used to control the information the user has access to 21 A view can be used to convert units e.g. to see salary in terms of rather than $, a view can be used to convert the values 24

24 A view can be treated as a table in its own right can be used in a query can be joined to another table or view 27 Modifying data in a view: you cannot use delete on multiple-table views you cannot use insert unless all the non-null columns in the underlying table are included in the view records updated through a multiple-table view must belong to the same underlying table records cannot be inserted or updated through a view which was defined using distinct new columns (e.g. ansal) cannot be updated 29

25 The END Introduction to SQL First 1OHT Course Review Chapter 1 SQL Fundamentals Chapter 2 SQL Plus Overview Chapter 3 Single row functions Chapter 4 Aggregating data and single row functions Chapter 5 Joins and sub queries

26 Chapter 6 Modifying Data (Insert, update, delete) Chapter 7 Managing tables (alter table, constraints) Chapter 8 Working with views Chapter 10 Creating users, granting access to users etc BOOK Introduction to Oracle 9i SQL Book topics covered approx 75% After completing 100% you are ready for OCP first paper