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Combining aggregate and non-aggregate values in SQL using Joins and Over clause

Prerequisite – Aggregate functions in SQL, Joins in SQL
Aggregate functions perform a calculation on a set of values and return a single value. Now, consider an employee table EMP and a department table DEPT with following structure:


Table – EMPLOYEE TABLE

Name Null Type
EMPNO NOT NULL NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7, 2)
COMM NUMBER(7, 2)
DEPTNO NUMBER(2)


Table – DEPARTMENT TABLE

Name Null Type
DEPTNO NUMBER(2)
DNAME VARCHAR2(14)
LOC VARCHAR2(13)



And the following results are needed:

  1. DISPLAY NAME, SAL, JOB OF EMP ALONG WITH MAX, MIN, AVG, TOTAL SAL OF THE EMPS DOING THE SAME JOB.
  2. DISPLAY DEPTNAME WITH NUMBER OF EMP WORKING IN IT.

The aggregated values can’t be directly used with non-aggregated values to obtain a result. Thus one can use the following concepts:

  • Using Joins –
    1. Create a sub-table containing the result of aggregated values.
    2. Using Join, use the results from the sub-table to display them with non-aggregated values.

    Solutions for the problem 1 using JOIN:

    SELECT ENAME, SAL, EMP.JOB, 
                SUBTABLE.MAXSAL, SUBTABLE.MINSAL, 
                SUBTABLE.AVGSAL, SUBTABLE.SUMSAL
    FROM EMP
    INNER JOIN
            (SELECT JOB, MAX(SAL) MAXSAL, MIN(SAL) 
                    MINSAL, AVG(SAL) AVGSAL, SUM(SAL) SUMSAL 
             FROM EMP 
              GROUP BY JOB) SUBTABLE
                      ON EMP.JOB = SUBTABLE.JOB; 

    Output for sample data:

    Ename Sal Job MaxSal MinSal AvgSal SumSal
    SCOTT 3300 ANALYST 3300 1925 2841.67 8525
    HENRY 1925 ANALYST 3300 1925 2841.67 8525
    FORD 3300 ANALYST 3300 1925 2841.67 8525
    SMITH 3300 CLERK 3300 1045 1746.25 6985
    MILLER 1430 CLERK 3300 1045 1746.25 6985

  • Using ‘Over’ clause –
    1. OVER CLAUSE ALONG WITH PARTION BY IS USED TO BRAKE UP DATA INTO PARTITIONS.
    2. THE SPECIFIED FUNCTION OPERATES FOR EACH PARTITION.

    Solutions for the problem 2 using OVER Clause:

    SELECT DISTINCT(DNAME),
    COUNT(ENAME) OVER (PARTITION BY EMP.DEPTNO) EMP
    FROM EMP
    RIGHT OUTER JOIN DEPT
    ON EMP.DEPTNO=DEPT.DEPTNO
    ORDER BY EMP DESC; 

    Dname Emp
    SALES 6
    RESEARCH 5
    ACCOUNTING 3
    OPERATIONS 0
    OTHERS 0



This article is attributed to GeeksforGeeks.org

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