4-1 Copyright  Oracle Corporation, All rights reserved. Displaying Data from Multiple Tables

4-2 Copyright  Oracle Corporation, All rights reserved. Objectives After completing this lesson, you should be able to do the following: Write SELECT statements to access data from more than one table using equality and nonequality joins View data that generally does not meet a join condition by using outer joins Join a table to itself After completing this lesson, you should be able to do the following: Write SELECT statements to access data from more than one table using equality and nonequality joins View data that generally does not meet a join condition by using outer joins Join a table to itself

4-3 Copyright  Oracle Corporation, All rights reserved. EMPNO DEPTNO LOC NEW YORK CHICAGO NEW YORK DALLAS CHICAGO CHICAGO rows selected. EMPNO DEPTNO LOC NEW YORK CHICAGO NEW YORK DALLAS CHICAGO CHICAGO rows selected. Obtaining Data from Multiple Tables EMPDEPT EMPNOENAME...DEPTNO KING BLAKE MILLER DEPTNO DNAME LOC ACCOUNTINGNEW YORK 20RESEARCHDALLAS 30SALESCHICAGO 40OPERATIONSBOSTON

4-4 Copyright  Oracle Corporation, All rights reserved. What Is a Join? Use a join to query data from more than one table. Write the join condition in the WHERE clause. Prefix the column name with the table name when the same column name appears in more than one table. Use a join to query data from more than one table. Write the join condition in the WHERE clause. Prefix the column name with the table name when the same column name appears in more than one table. SELECTtable1.column, table2.column FROMtable1, table2 WHEREtable1.column1 = table2.column2; SELECTtable1.column, table2.column FROMtable1, table2 WHEREtable1.column1 = table2.column2;

4-5 Copyright  Oracle Corporation, All rights reserved. What Is an Equijoin? EMP DEPT EMPNO ENAME DEPTNO KING BLAKE CLARK JONES MARTIN ALLEN TURNER JAMES WARD FORD SMITH rows selected. DEPTNO DNAME LOC ACCOUNTING NEW YORK 30 SALES CHICAGO 10 ACCOUNTINGNEW YORK 20 RESEARCHDALLAS 30 SALES CHICAGO 20 RESEARCHDALLAS rows selected. Primary key Foreign key

4-6 Copyright  Oracle Corporation, All rights reserved. Retrieving Records with Equijoins SQL> SELECT emp.empno, emp.ename, emp.deptno, 2dept.deptno, dept.loc 3 FROM emp, dept 4 WHERE emp.deptno=dept.deptno; EMPNO ENAME DEPTNO DEPTNO LOC KING NEW YORK 7698 BLAKE CHICAGO 7782 CLARK NEW YORK 7566 JONES DALLAS rows selected.

4-7 Copyright  Oracle Corporation, All rights reserved. Using Table Aliases Simplify queries by using table aliases. SQL> SELECT emp.empno, emp.ename, emp.deptno, 2 dept.deptno, dept.loc 3 FROM emp, dept 4 WHERE emp.deptno=dept.deptno; SQL> SELECT e.empno, e.ename, e.deptno, 2 d.deptno, d.loc 3 FROM emp e, dept d 4 WHERE e.deptno=d.deptno;

4-8 Copyright  Oracle Corporation, All rights reserved. Joining More Than Two Tables NAMECUSTID JOCKSPORTS 100 TKB SPORT SHOP 101 VOLLYRITE 102 JUST TENNIS 103 K+T SPORTS 105 SHAPE UP 106 WOMENS SPORTS rows selected. NAMECUSTID JOCKSPORTS 100 TKB SPORT SHOP 101 VOLLYRITE 102 JUST TENNIS 103 K+T SPORTS 105 SHAPE UP 106 WOMENS SPORTS rows selected. CUSTOMER CUSTID ORDID rows selected. CUSTID ORDID rows selected.ORD ORDID ITEMID rows selected. ORDID ITEMID rows selected.ITEM

4-9 Copyright  Oracle Corporation, All rights reserved. Aggregating Data Using Group Functions

4-10 Copyright  Oracle Corporation, All rights reserved. Objectives After completing this lesson, you should be able to do the following: Identify the available group functions Describe the use of group functions Group data using the GROUP BY clause Include or exclude grouped rows by using the HAVING clause After completing this lesson, you should be able to do the following: Identify the available group functions Describe the use of group functions Group data using the GROUP BY clause Include or exclude grouped rows by using the HAVING clause

4-11 Copyright  Oracle Corporation, All rights reserved. What Are Group Functions? Group functions operate on sets of rows to give one result per group. EMP “maximum salary in salary in the EMP table” DEPTNO SAL MAX(SAL)

4-12 Copyright  Oracle Corporation, All rights reserved. Types of Group Functions AVG COUNT MAX MIN STDDEV SUM VARIANCE AVG COUNT MAX MIN STDDEV SUM VARIANCE

4-13 Copyright  Oracle Corporation, All rights reserved. Using Group Functions SELECTcolumn, group_function(column) FROMtable [WHEREcondition] [ORDER BYcolumn];

4-14 Copyright  Oracle Corporation, All rights reserved. Using AVG and SUM Functions AVG(SAL) MAX(SAL) MIN(SAL) SUM(SAL) You can use AVG and SUM for numeric data. SQL> SELECTAVG(sal), MAX(sal), 2MIN(sal), SUM(sal) 3FROMemp 4WHEREjob LIKE 'SALES%';

4-15 Copyright  Oracle Corporation, All rights reserved. Using MIN and MAX Functions You can use MIN and MAX for any datatype. SQL> SELECTMIN(hiredate), MAX(hiredate) 2 FROMemp; MIN(HIRED MAX(HIRED DEC JAN-83

4-16 Copyright  Oracle Corporation, All rights reserved. Using the COUNT Function COUNT(*) SQL> SELECTCOUNT(*) 2 FROMemp 3 WHEREdeptno = 30; COUNT(*) returns the number of rows in a table.

4-17 Copyright  Oracle Corporation, All rights reserved. Group Functions and Null Values Group functions ignore null values in the column. SQL> SELECT AVG(comm) 2 FROM emp; AVG(COMM)

4-18 Copyright  Oracle Corporation, All rights reserved. Creating Groups of Data EMP “average salary in EMP table for each department” DEPTNO SAL DEPTNO AVG(SAL)

4-19 Copyright  Oracle Corporation, All rights reserved. Creating Groups of Data: GROUP BY Clause SELECTcolumn, group_function(column) FROMtable [WHEREcondition] [GROUP BYgroup_by_expression] [ORDER BYcolumn]; Divide rows in a table into smaller groups by using the GROUP BY clause.

4-20 Copyright  Oracle Corporation, All rights reserved. Using the GROUP BY Clause All columns in the SELECT list that are not in group functions must be in the GROUP BY clause. SQL> SELECT deptno, AVG(sal) 2 FROM emp 3 GROUP BY deptno; DEPTNO AVG(SAL)

4-21 Copyright  Oracle Corporation, All rights reserved. Using the GROUP BY Clause The GROUP BY column does not have to be in the SELECT list. SQL> SELECT AVG(sal) 2 FROM emp 3 GROUP BY deptno; AVG(SAL)

4-22 Copyright  Oracle Corporation, All rights reserved. Grouping by More Than One Column EMP “sum salaries in the EMP table for each job, grouped by department” DEPTNO JOB SAL MANAGER PRESIDENT CLERK CLERK CLERK ANALYST MANAGER SALESMAN MANAGER SALESMAN CLERK SALESMAN SALESMAN 1250 JOB SUM(SAL) CLERK 1300 MANAGER 2450 PRESIDENT 5000 ANALYST 6000 CLERK 1900 MANAGER 2975 CLERK 950 MANAGER 2850 SALESMAN 5600 DEPTNO

4-23 Copyright  Oracle Corporation, All rights reserved. Using the GROUP BY Clause on Multiple Columns SQL> SELECT deptno, job, sum(sal) 2 FROM emp 3 GROUP BY deptno, job; DEPTNO JOB SUM(SAL) CLERK MANAGER PRESIDENT ANALYST CLERK rows selected.

4-24 Copyright  Oracle Corporation, All rights reserved. Illegal Queries Using Group Functions Any column or expression in the SELECT list that is not an aggregate function must be in the GROUP BY clause. SQL> SELECTdeptno, COUNT(ename) 2 FROMemp; SQL> SELECTdeptno, COUNT(ename) 2 FROMemp; SELECT deptno, COUNT(ename) * ERROR at line 1: ORA-00937: not a single-group group function SELECT deptno, COUNT(ename) * ERROR at line 1: ORA-00937: not a single-group group function Column missing in the GROUP BY clause

4-25 Copyright  Oracle Corporation, All rights reserved. Illegal Queries Using Group Functions You cannot use the WHERE clause to restrict groups. You use the HAVING clause to restrict groups. You cannot use the WHERE clause to restrict groups. You use the HAVING clause to restrict groups. SQL> SELECT deptno, AVG(sal) 2 FROM emp 3 WHERE AVG(sal) > GROUP BY deptno; SQL> SELECT deptno, AVG(sal) 2 FROM emp 3 WHERE AVG(sal) > GROUP BY deptno; WHERE AVG(sal) > 2000 * ERROR at line 3: ORA-00934: group function is not allowed here WHERE AVG(sal) > 2000 * ERROR at line 3: ORA-00934: group function is not allowed here Cannot use the WHERE clause to restrict groups to restrict groups Cannot use the WHERE clause to restrict groups to restrict groups

4-26 Copyright  Oracle Corporation, All rights reserved. Excluding Group Results “maximum salary per department greater than $2900” EMP DEPTNO SAL DEPTNO MAX(SAL)

4-27 Copyright  Oracle Corporation, All rights reserved. Excluding Group Results: HAVING Clause Use the HAVING clause to restrict groups – Rows are grouped. – The group function is applied. – Groups matching the HAVING clause are displayed. Use the HAVING clause to restrict groups – Rows are grouped. – The group function is applied. – Groups matching the HAVING clause are displayed. SELECTcolumn, group_function FROMtable [WHEREcondition] [GROUP BYgroup_by_expression] [HAVINGgroup_condition] [ORDER BYcolumn];

4-28 Copyright  Oracle Corporation, All rights reserved. Using the HAVING Clause SQL> SELECT deptno, max(sal) 2 FROM emp 3 GROUP BY deptno 4 HAVING max(sal)>2900; DEPTNO MAX(SAL)

4-29 Copyright  Oracle Corporation, All rights reserved. Using the HAVING Clause SQL> SELECT job, SUM(sal) PAYROLL 2 FROM emp 3 WHERE job NOT LIKE 'SALES%' 4 GROUP BY job 5 HAVING SUM(sal)> ORDER BY SUM(sal); JOB PAYROLL ANALYST 6000 MANAGER 8275

4-30 Copyright  Oracle Corporation, All rights reserved. Nesting Group Functions SQL> SELECT max(avg(sal)) 2 FROM emp 3 GROUP BY deptno; MAX(AVG(SAL)) Display the maximum average salary.

4-31 Copyright  Oracle Corporation, All rights reserved. Summary SELECTcolumn, group_function (column) FROMtable [WHEREcondition] [GROUP BYgroup_by_expression] [HAVINGgroup_condition] [ORDER BYcolumn]; Order of evaluation of the clauses: WHERE clause GROUP BY clause HAVING clause Order of evaluation of the clauses: WHERE clause GROUP BY clause HAVING clause

4-32 Copyright  Oracle Corporation, All rights reserved. Sub Queries

4-33 Copyright  Oracle Corporation, All rights reserved. Objectives After completing this lesson, you should be able to do the following: Describe the types of problems that subqueries can solve Define subqueries List the types of subqueries Write single-row and multiple-row subqueries After completing this lesson, you should be able to do the following: Describe the types of problems that subqueries can solve Define subqueries List the types of subqueries Write single-row and multiple-row subqueries

4-34 Copyright  Oracle Corporation, All rights reserved. Using a Subquery to Solve a Problem “Who has a salary greater than Jones’s?” “Which employees have a salary greater than Jones’s salary?” Main Query ? “What is Jones’s salary?” ? Subquery

4-35 Copyright  Oracle Corporation, All rights reserved. Subqueries The subquery (inner query) executes once before the main query. The result of the subquery is used by the main query (outer query). The subquery (inner query) executes once before the main query. The result of the subquery is used by the main query (outer query). SELECTselect_list FROMtable WHEREexpr operator (SELECTselect_list FROMtable);

4-36 Copyright  Oracle Corporation, All rights reserved SQL> SELECT ename 2 FROM emp 3 WHERE sal > 4 (SELECT sal 5 FROM emp 6 WHERE empno=7566); Using a Subquery ENAME KING FORD SCOTT ENAME KING FORD SCOTT

4-37 Copyright  Oracle Corporation, All rights reserved. Guidelines for Using Subqueries Enclose subqueries in parentheses. Place subqueries on the right side of the comparison operator. Do not add an ORDER BY clause to a subquery. Use single-row operators with single- row subqueries. Use multiple-row operators with multiple-row subqueries. Enclose subqueries in parentheses. Place subqueries on the right side of the comparison operator. Do not add an ORDER BY clause to a subquery. Use single-row operators with single- row subqueries. Use multiple-row operators with multiple-row subqueries.

4-38 Copyright  Oracle Corporation, All rights reserved. Types of Subqueries Single-row subquery Main query Subquery returns CLERK Multiple-row subquery CLERKMANAGER Main query Subquery returns Multiple-column subquery CLERK 7900 MANAGER 7698 Main query Subquery returns

4-39 Copyright  Oracle Corporation, All rights reserved. Single-Row Subqueries Return only one row Use single-row comparison operators Return only one row Use single-row comparison operators Operator = > >= < <= <> Meaning Equal to Greater than Greater than or equal to Less than Less than or equal to Not equal to

4-40 Copyright  Oracle Corporation, All rights reserved. Executing Single-Row Subqueries CLERK 1100 ENAME JOB MILLER CLERK ENAME JOB MILLER CLERK SQL> SELECT ename, job 2 FROM emp 3 WHERE job = 4(SELECT job 5 FROM emp 6 WHERE empno = 7369) 7 AND sal > 8(SELECT sal 9FROMemp 10WHEREempno = 7876);

4-41 Copyright  Oracle Corporation, All rights reserved. Using Group Functions in a Subquery 800 ENAME JOB SAL SMITH CLERK 800 ENAME JOB SAL SMITH CLERK 800 SQL> SELECTename, job, sal 2 FROMemp 3 WHEREsal = 4(SELECTMIN(sal) 5FROMemp);

4-42 Copyright  Oracle Corporation, All rights reserved. HAVING Clause with Subqueries The Oracle Server executes subqueries first. The Oracle Server returns results into the main query’s HAVING clause. The Oracle Server executes subqueries first. The Oracle Server returns results into the main query’s HAVING clause. 800 SQL> SELECTdeptno, MIN(sal) 2 FROMemp 3 GROUP BYdeptno 4 HAVINGMIN(sal) > 5(SELECTMIN(sal) 6FROMemp 7WHEREdeptno = 20);

4-43 Copyright  Oracle Corporation, All rights reserved. What Is Wrong with This Statement? ERROR: ORA-01427: single-row subquery returns more than one row no rows selected ERROR: ORA-01427: single-row subquery returns more than one row no rows selected SQL> SELECT empno, ename 2 FROM emp 3 WHERE sal = 4(SELECT MIN(sal) 5FROM emp 6GROUP BY deptno); Single-row operator with multiple-row subquery

4-44 Copyright  Oracle Corporation, All rights reserved. Will This Statement Work? no rows selected Subquery returns no values SQL> SELECT ename, job 2 FROM emp 3 WHERE job = 4(SELECTjob 5FROMemp 6WHEREename='SMYTHE');

4-45 Copyright  Oracle Corporation, All rights reserved. Multiple-Row Subqueries Return more than one row Use multiple-row comparison operators i.e. IN operator Return more than one row Use multiple-row comparison operators i.e. IN operator

4-46 Copyright  Oracle Corporation, All rights reserved. Summary Subqueries are useful when a query is based on unknown values. SELECTselect_list FROMtable WHEREexpr operator (SELECT select_list FROM table);