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- 1. Copyright OracleCorporation, 1997. All rights reserved. 5 Subqueries
- 2. 5-2 Copyright Oracle Corporation, 1997. All rights reserved. Objectives At the end of this lesson, you should be able to: • Describe the types of problems that subqueries can solve • Define subqueries • List the types of subqueries • Write single-row and multiple-row subqueries
- 3. 5-3 Copyright Oracle Corporation, 1997. 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. 5-4 Copyright Oracle Corporation, 1997. 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). SELECT select_list FROM table WHERE expr operator (SELECT select_list FROM table);
- 5. 5-5 Copyright Oracle Corporation, 1997. All rights reserved. 2975 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
- 6. 5-6 Copyright Oracle Corporation, 1997. 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.
- 7. 5-7 Copyright Oracle Corporation, 1997. All rights reserved. Types of Subqueries • Single-row subquery Main query Subquery returns CLERK • Multiple-row subquery CLERK MANAGER Main query Subquery returns • Multiple-column subquery CLERK 7900 MANAGER 7698 Main query Subquery returns
- 8. 5-8 Copyright Oracle Corporation, 1997. All rights reserved. Single-Row Subqueries • 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
- 9. 5-9 Copyright Oracle Corporation, 1997. All rights reserved. Executing Single-Row Subqueries CLERK 1100 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 9 FROM emp 10 WHERE empno = 7876);
- 10. 5-10 Copyright Oracle Corporation, 1997. All rights reserved. Using Group Functions in a Subquery 800 ENAME JOB SAL ---------- --------- --------- SMITH CLERK 800 SQL> SELECT ename, job, sal 2 FROM emp 3 WHERE sal = 4 (SELECT MIN(sal) 5 FROM emp);
- 11. 5-11 Copyright Oracle Corporation, 1997. All rights reserved. HAVING Clause with Subqueries • The Oracle10 Server executes subqueries first. • The Oracle10 Server returns results into the main query’s HAVING clause. 800 SQL> SELECT deptno, MIN(sal) 2 FROM emp 3 GROUP BY deptno 4 HAVING MIN(sal) > 5 (SELECT MIN(sal) 6 FROM emp 7 WHERE deptno = 20);
- 12. 5-12 Copyright Oracle Corporation, 1997. All rights reserved. What Is Wrong with This Statement? 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) 5 FROM emp 6 GROUP BY deptno);
- 13. 5-13 Copyright Oracle Corporation, 1997. All rights reserved. Will This Statement Work? no rows selected SQL> SELECT ename, job 2 FROM emp 3 WHERE job = 4 (SELECT job 5 FROM emp 6 WHERE ename='SMYTHE');
- 14. 5-14 Copyright Oracle Corporation, 1997. All rights reserved. Multiple-Row Subqueries • Return more than one row • Use multiple-row comparison operators Operator IN ANY ALL Meaning Equal to any member in the list Compare value to each value returned by the subquery Compare value to every value returned by the subquery
- 15. 5-15 Copyright Oracle Corporation, 1997. All rights reserved. Using ANY Operator in Multiple-Row Subqueries 950 800 1100 1300 EMPNO ENAME JOB --------- ---------- --------- 7654 MARTIN SALESMAN 7521 WARD SALESMAN SQL> SELECT empno, ename, job 2 FROM emp 3 WHERE sal < ANY 4 (SELECT sal 5 FROM emp 6 WHERE job = 'CLERK') 7 AND job <> 'CLERK';
- 16. 5-16 Copyright Oracle Corporation, 1997. All rights reserved. Using ALL Operator in Multiple-Row Subqueries 2916.6667 2175 1566.6667 EMPNO ENAME JOB --------- ---------- --------- 7839 KING PRESIDENT 7566 JONES MANAGER 7902 FORD ANALYST 7788 SCOTT ANALYST SQL> SELECT empno, ename, job 2 FROM emp 3 WHERE sal > ALL 4 (SELECT avg(sal) 5 FROM emp 6 GROUP BY deptno)
- 17. 5-17 Copyright Oracle Corporation, 1997. All rights reserved. Multiple-Column Subqueries Main query MANAGER 10 Subquery SALESMAN 30 MANAGER 10 CLERK 20 Main query compares MANAGER 10 Values from a multiple-row and multiple-column subquery SALESMAN 30 MANAGER 10 CLERK 20 to
- 18. 5-18 Copyright Oracle Corporation, 1997. All rights reserved. Using Multiple-Column Subqueries Display the name, department number, salary, and commission of any employee whose salary and commission matches both the commission and salary of any employee in department 30. SQL> SELECT ename, deptno, sal, comm 2 FROM emp 3 WHERE (sal, NVL(comm,-1)) IN 4 (SELECT sal, NVL(comm,-1) 5 FROM emp 6 WHERE deptno = 30);
- 19. 5-19 Copyright Oracle Corporation, 1997. All rights reserved. Column Comparisons Pairwise SAL COMM 1600 300 1250 500 1250 1400 2850 1500 0 950 Nonpairwise SAL COMM 1600 300 1250 500 1250 1400 2850 1500 0 950
- 20. 5-20 Copyright Oracle Corporation, 1997. All rights reserved. Nonpairwise Comparison Subquery SQL> SELECT ename, deptno, sal, comm 2 FROM emp 3 WHERE sal IN (SELECT sal 4 FROM emp 5 WHERE deptno = 30) 6 AND 7 NVL(comm,-1) IN (SELECT NVL(comm,-1) 8 FROM emp 9 WHERE deptno = 30); Display the name, department number, salary, and commission of any employee whose salary and commission matches the commission and salary of any employee in department 30.
- 21. 5-21 Copyright Oracle Corporation, 1997. All rights reserved. Modifying the EMP Table • Assume that salary and commission for Clark are modified. • Salary is changed to $1500 and commission to $300. ENAME SAL COMM ---------- --------- --------- ... CLARK 1500 300 ... ALLEN 1600 300 TURNER 1500 0 ... 14 rows selected.
- 22. 5-22 Copyright Oracle Corporation, 1997. All rights reserved. Pairwise Subquery SQL> SELECT ename, deptno, sal, comm 2 FROM emp 3 WHERE (sal, NVL(comm,-1)) IN 4 (SELECT sal, NVL(comm,-1) 5 FROM emp 6 WHERE deptno = 30); ENAME DEPTNO SAL COMM ---------- --------- --------- --------- JAMES 30 950 WARD 30 1250 500 MARTIN 30 1250 1400 TURNER 30 1500 0 ALLEN 30 1600 300 BLAKE 30 2850 6 rows selected.
- 23. 5-23 Copyright Oracle Corporation, 1997. All rights reserved. SQL> SELECT ename,deptno, sal, comm 2 FROM emp 3 WHERE sal IN (SELECT sal 4 FROM emp 5 WHERE deptno = 30) 6 AND 7 NVL(comm,-1) IN (SELECT NVL(comm,-1) 8 FROM emp 9 WHERE deptno = 30); Nonpairwise Subquery ENAME DEPTNO SAL COMM ---------- --------- --------- --------- JAMES 30 950 BLAKE 30 2850 TURNER 30 1500 0 CLARK 10 1500 300 ... 7 rows selected.
- 24. 5-24 Copyright Oracle Corporation, 1997. All rights reserved. Null Values in a Subquery SQL> SELECT employee.ename 2 FROM emp employee 3 WHERE employee.empno NOT IN (SELECT manager.mgr FROM emp manager); no rows selected.
- 25. 5-25 Copyright Oracle Corporation, 1997. All rights reserved. Using a Subquery in the FROM Clause ENAME SAL DEPTNO SALAVG ---------- --------- --------- ---------- KING 5000 10 2916.6667 JONES 2975 20 2175 SCOTT 3000 20 2175 ... 6 rows selected. SQL> SELECT a.ename, a.sal, a.deptno, b.salavg 2 FROM emp a, (SELECT deptno, avg(sal) salavg 3 FROM emp 4 GROUP BY deptno) b 5 WHERE a.deptno = b.deptno 6 AND a.sal > b.salavg;
- 26. 5-26 Copyright Oracle Corporation, 1997. All rights reserved. Summary • A multiple-column subquery returns more than one column. • Column comparisons in a multiple- column comparisons can be pairwise or nonpairwise. • A multiple-column subquery can also be used in the FROM clause of a SELECT statement.
- 27. 5-27 Copyright Oracle Corporation, 1997. All rights reserved. Practice Overview Creating subqueries