Copyright  Oracle Corporation, All rights reserved. 5 Aggregating Data Using Group Functions

5-2 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

5-3 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)

5-4 Copyright  Oracle Corporation, All rights reserved. Types of Group Functions AVG COUNT MAX MIN STDDEV SUM VARIANCE AVG COUNT MAX MIN STDDEV SUM VARIANCE

5-5 Copyright  Oracle Corporation, All rights reserved. Using Group Functions SELECTcolumn, group_function(column) FROMtable [WHEREcondition] [ORDER BYcolumn];

5-6 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%';

5-7 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

5-8 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.

5-9 Copyright  Oracle Corporation, All rights reserved. Using the COUNT Function COUNT(expr) returns the number of nonnull rows. SQL> SELECTCOUNT(comm) 2 FROMemp 3 WHEREdeptno = 30; COUNT(COMM)

5-10 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)

5-11 Copyright  Oracle Corporation, All rights reserved. Using the NVL Function with Group Functions The NVL function forces group functions to include null values. SQL> SELECT AVG(NVL(comm,0)) 2 FROM emp; AVG(NVL(COMM,0))

5-12 Copyright  Oracle Corporation, All rights reserved. Creating Groups of Data EMP “average salary in EMP table for each department” DEPTNO SAL DEPTNO AVG(SAL)

5-13 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.

5-14 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)

5-15 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)

5-16 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

5-17 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.

5-18 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

5-19 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

5-20 Copyright  Oracle Corporation, All rights reserved. Excluding Group Results “maximum salary per department greater than $2900” EMP DEPTNO SAL DEPTNO MAX(SAL)

5-21 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];

5-22 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)

5-23 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

5-24 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.

5-25 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

5-26 Copyright  Oracle Corporation, All rights reserved. Practice Overview Showing different queries that use group functions Grouping by rows to achieve more than one result Excluding groups by using the HAVING clause Showing different queries that use group functions Grouping by rows to achieve more than one result Excluding groups by using the HAVING clause

5-27 Copyright  Oracle Corporation, All rights reserved.

5-28 Copyright  Oracle Corporation, All rights reserved.

5-29 Copyright  Oracle Corporation, All rights reserved.

5-30 Copyright  Oracle Corporation, All rights reserved.