Post on 14-Jan-2016
description
SQL: Part 3SQL: Part 3
Original materials supplied by the Oracle Academic Initiative (OAI). Edited for classroom use by Professor Laku Chidambaram.
Not for commercial use. Do not redistribute.
Original materials supplied by the Oracle Academic Initiative (OAI). Edited for classroom use by Professor Laku Chidambaram.
Not for commercial use. Do not redistribute.
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OUTLINEOUTLINE
Group FunctionsGroup Functions
Sub-queriesSub-queries
Set OperationsSet Operations
Group FunctionsGroup Functions
Sub-queriesSub-queries
Set OperationsSet Operations
Group FunctionsGroup Functions
Original materials supplied by the Oracle Academic Initiative (OAI); edited for classroom use by Professor Laku Chidambaram. Do not redistribute.Original materials supplied by the Oracle Academic Initiative (OAI); edited for classroom use by Professor Laku Chidambaram. Do not redistribute.
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What Are Group Functions?What Are Group Functions?Group functions operate on sets of rows to give Group functions operate on sets of rows to give one result per group.one result per group.Group functions operate on sets of rows to give Group functions operate on sets of rows to give one result per group.one result per group.EMPEMP
““maximum maximum salary in salary in
the EMP table”the EMP table”
DEPTNO SAL--------- --------- 10 2450 10 5000 10 1300 20 800 20 1100 20 3000 20 3000 20 2975 30 1600 30 2850 30 1250 30 950 30 1500 30 1250
MAX(SAL)
---------
5000
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Types of Group FunctionsTypes of Group Functions
• AVG
• COUNT
• MAX
• MIN
• STDDEV
• SUM
• VARIANCE
• AVG
• COUNT
• MAX
• MIN
• STDDEV
• SUM
• VARIANCE
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Using Group FunctionsUsing Group Functions
SELECT [column,] group_function(column)FROM table[WHERE condition][GROUP BY column][ORDER BY column]
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Using AVG and SUM FunctionsUsing AVG and SUM Functions
AVG(SAL) MAX(SAL) MIN(SAL) SUM(SAL)-------- --------- --------- --------- 1400 1600 1250 5600
You can use AVG and SUM for numeric data.You can use AVG and SUM for numeric data.You can use AVG and SUM for numeric data.You can use AVG and SUM for numeric data.
SQL> SELECT AVG(sal), MAX(sal), 2 MIN(sal), SUM(sal) 3 FROM emp 4 WHERE job LIKE 'SALES%'
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Using MIN and MAX FunctionsUsing MIN and MAX Functions
You can use MIN and MAX for any datatype.You can use MIN and MAX for any datatype.You can use MIN and MAX for any datatype.You can use MIN and MAX for any datatype.
SQL> SELECT MIN(hiredate), MAX(hiredate) 2 FROM emp
MIN(HIRED MAX(HIRED--------- ---------17-DEC-80 12-JAN-83
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Using the COUNT FunctionUsing the COUNT Function
COUNT(*)--------- 6
SQL> SELECT COUNT(*) 2 FROM emp 3 WHERE deptno = 30
COUNT(*) returns the number of rows in a COUNT(*) returns the number of rows in a table.table.COUNT(*) returns the number of rows in a COUNT(*) returns the number of rows in a table.table.
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Using the COUNT FunctionUsing the COUNT Function
COUNT(COUNT(exprexpr) returns the number of ) returns the number of nonnull rows.nonnull rows.COUNT(COUNT(exprexpr) returns the number of ) returns the number of nonnull rows.nonnull rows.
SQL> SELECT COUNT(comm) 2 FROM emp 3 WHERE deptno = 30
COUNT(COMM)----------- 4
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Group Functions and Null ValuesGroup Functions and Null Values
Group functions ignore null values in the Group functions ignore null values in the column.column.Group functions ignore null values in the Group functions ignore null values in the column.column.
SQL> SELECT AVG(comm) 2 FROM emp
AVG(COMM)--------- 550
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Using the ISNULL Function with Group Functions
Using the ISNULL Function with Group Functions
The ISNULL function forces group The ISNULL function forces group functions to include null values.functions to include null values.The ISNULL function forces group The ISNULL function forces group functions to include null values.functions to include null values.
SQL> SELECT AVG(ISNULL(comm,0)) 2 FROM emp
AVG(ISNULL(COMM,0))---------------- 157.14286
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Creating Groups of Data Creating Groups of Data
EMPEMP
““averageaveragesalary salary in EMPin EMPtable table
for each for each department”department”
2916.66672916.6667
21752175
1566.66671566.6667
DEPTNO SAL--------- --------- 10 2450 10 5000 10 1300 20 800 20 1100 20 3000 20 3000 20 2975 30 1600 30 2850 30 1250 30 950 30 1500 30 1250
DEPTNO AVG(SAL)
------- ---------
10 2916.6667
20 2175
30 1566.6667
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Creating Groups of Data: GROUP BY Clause
Creating Groups of Data: GROUP BY Clause
SELECT column, group_function(column)FROM table[WHERE condition][GROUP BY group_by_expression][ORDER BY column]
Divide rows in a table into smaller groups Divide rows in a table into smaller groups by using the GROUP BY clause.by using the GROUP BY clause.Divide rows in a table into smaller groups Divide rows in a table into smaller groups by using the GROUP BY clause.by using the GROUP BY clause.
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Using the GROUP BY Clause Using the GROUP BY Clause
All columns in the SELECT list that are not All columns in the SELECT list that are not in group functions must be in the GROUP in group functions must be in the GROUP BY clause.BY clause.
All columns in the SELECT list that are not All columns in the SELECT list that are not in group functions must be in the GROUP in group functions must be in the GROUP BY clause.BY clause.
SQL> SELECT deptno, AVG(sal) 2 FROM emp 3 GROUP BY deptno
DEPTNO AVG(SAL)--------- --------- 10 2916.6667 20 2175 30 1566.6667
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Using the GROUP BY Clause Using the GROUP BY Clause
The GROUP BY column does not have to The GROUP BY column does not have to be in the SELECT list.be in the SELECT list.The GROUP BY column does not have to The GROUP BY column does not have to be in the SELECT list.be in the SELECT list.
SQL> SELECT AVG(sal) 2 FROM emp 3 GROUP BY deptno
AVG(SAL)--------- 2916.6667 21751566.6667
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Grouping by More Than One ColumnGrouping by More Than One Column
EMPEMP
““sum salaries in sum salaries in the EMP tablethe EMP tablefor each job, for each job, grouped by grouped by department”department”
DEPTNO JOB SAL
--------- --------- ---------
10 MANAGER 2450
10 PRESIDENT 5000
10 CLERK 1300
20 CLERK 800
20 CLERK 1100
20 ANALYST 3000
20 ANALYST 3000
20 MANAGER 2975
30 SALESMAN 1600
30 MANAGER 2850
30 SALESMAN 1250
30 CLERK 950
30 SALESMAN 1500
30 SALESMAN 1250
JOB SUM(SAL)
--------- ---------
CLERK 1300
MANAGER 2450
PRESIDENT 5000
ANALYST 6000
CLERK 1900
MANAGER 2975
CLERK 950
MANAGER 2850
SALESMAN 5600
DEPTNO
--------
10
10
10
20
20
20
30
30
30
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Using the GROUP BY Clause on Multiple Columns
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)--------- --------- --------- 10 CLERK 1300 10 MANAGER 2450 10 PRESIDENT 5000 20 ANALYST 6000 20 CLERK 1900...9 rows selected.
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Illegal Queries Using Group Functions
Illegal Queries Using Group Functions
Any column or expression in the SELECT Any column or expression in the SELECT list that is not an aggregate function must list that is not an aggregate function must be in the GROUP BY clause.be in the GROUP BY clause.
Any column or expression in the SELECT Any column or expression in the SELECT list that is not an aggregate function must list that is not an aggregate function must be in the GROUP BY clause.be in the GROUP BY clause.
SQL> SELECT deptno, COUNT(ename) 2 FROM emp
SQL> SELECT deptno, COUNT(ename) 2 FROM emp
SELECT deptno, COUNT(ename) *ERROR at line 1: not a single-group group function
SELECT deptno, COUNT(ename) *ERROR at line 1: not a single-group group function
Column missing in the GROUP BY clause
Column missing in the GROUP BY clause
Column missing in the GROUP BY clause
Column missing in the GROUP BY clause
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Illegal Queries Using Group Functions
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) > 2000 4 GROUP BY deptno
SQL> SELECT deptno, AVG(sal) 2 FROM emp 3 WHERE AVG(sal) > 2000 4 GROUP BY deptno
WHERE AVG(sal) > 2000 *ERROR at line 3: group function is not allowed here
WHERE AVG(sal) > 2000 *ERROR at line 3: group function is not allowed hereCannot use the WHERE clause
Cannot use the WHERE clause
to
restrict groups
to restrict groups
Cannot use the WHERE clause
Cannot use the WHERE clause
to
restrict groups
to restrict groups
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Excluding Group ResultsExcluding Group Results
““maximummaximumsalarysalary
per departmentper departmentgreater thangreater than
$2900”$2900”
EMPEMP
50005000
30003000
28502850
DEPTNO SAL
--------- ---------
10 2450
10 5000
10 1300
20 800
20 1100
20 3000
20 3000
20 2975
30 1600
30 2850
30 1250
30 950
30 1500
30 1250
DEPTNO MAX(SAL)
--------- ---------
10 5000
20 3000
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Excluding Group Results: HAVING Clause
Excluding Group Results: HAVING Clause
Use the HAVING clause to restrict groupsUse 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 groupsUse the HAVING clause to restrict groups
– Rows are grouped.
– The group function is applied.
– Groups matching the HAVING clause are displayed.
SELECT column, group_functionFROM table[WHERE condition][GROUP BY group_by_expression][HAVING group_condition][ORDER BY column]
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Using the HAVING ClauseUsing the HAVING Clause
SQL> SELECT deptno, max(sal) 2 FROM emp 3 GROUP BY deptno 4 HAVING max(sal)>2900
DEPTNO MAX(SAL)--------- --------- 10 5000 20 3000
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Using the HAVING ClauseUsing 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)>5000 6 ORDER BY SUM(sal)
JOB PAYROLL--------- ---------ANALYST 6000MANAGER 8275
Sub-queriesSub-queries
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What Is a Subquery?What Is a Subquery?
A subquery is a SELECT statement A subquery is a SELECT statement embedded in a clause of another SQL embedded in a clause of another SQL statement.statement.
A subquery is a SELECT statement A subquery is a SELECT statement embedded in a clause of another SQL embedded in a clause of another SQL statement.statement.
SELECT . . . FROM . . .WHERE . . .
(SELECT . . .FROM . . .WHERE . . .)
MainMainQueryQuery
SubquerySubquery
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SubqueriesSubqueries
• 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).
SELECT select_listFROM tableWHERE expr operator (SELECT select_list
FROM table)
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2975
SQL> SELECT ename 2 FROM emp 3 WHERE sal > 4 (SELECT sal 5 FROM emp 6 WHERE empno = 7566)
Using a SubqueryUsing a Subquery
ENAME ---------- KING FORD SCOTT
ENAME ---------- KING FORD SCOTT
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Correlated SubqueriesCorrelated Subqueries
Used to affect row-by-row processing, Used to affect row-by-row processing, each subquery is executed once for every each subquery is executed once for every row of the outer query.row of the outer query.
Used to affect row-by-row processing, Used to affect row-by-row processing, each subquery is executed once for every each subquery is executed once for every row of the outer query.row of the outer query.
GETcandidate row
EXECUTEinner query using candidate row value
USEvalue(s) from inner query to qualify
candidate row
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Correlated SubqueriesCorrelated Subqueries
SELECT outer1, outer2, ... FROM table1 alias1 WHERE outer1 operator
(SELECT inner1 FROM table2 alias2 WHERE alias1.outer2 =
alias2.inner1)
The subquery references a column from subquery references a column from a table in the parent query.a table in the parent query.The subquery references a column from subquery references a column from a table in the parent query.a table in the parent query.
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Using Correlated SubqueriesUsing Correlated Subqueries
Each time the outer queryis processed the
inner query is evaluated.
SQL> SELECT empno, sal, deptno 2 FROM emp outr 3 WHERE sal > (SELECT AVG(sal) 4 FROM emp innr 5 WHERE outr.deptno = innr.deptno)
EMPNO SAL DEPTNO-------- --------- --------- 7839 5000 10 7698 2850 30 7566 2975 20 ... 6 rows selected.
EMPNO SAL DEPTNO-------- --------- --------- 7839 5000 10 7698 2850 30 7566 2975 20 ... 6 rows selected.
Find all employees who make more than Find all employees who make more than the average salary in their department.the average salary in their department.Find all employees who make more than Find all employees who make more than the average salary in their department.the average salary in their department.
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Using the EXISTS OperatorUsing the EXISTS Operator
• If a subquery row value is found:
– The search does not continue in the inner query.
– The condition is flagged TRUE.
• If a subquery row value is not found:
– The condition is flagged FALSE.
– The search continues in the inner query.
• If a subquery row value is found:
– The search does not continue in the inner query.
– The condition is flagged TRUE.
• If a subquery row value is not found:
– The condition is flagged FALSE.
– The search continues in the inner query.
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Find employees who have at least one person reporting to them.
Using the EXISTS OperatorUsing the EXISTS Operator
EMPNO ENAME JOB DEPTNO--------- ---------- --------- --------- 7839 KING PRESIDENT 10 7698 BLAKE MANAGER 30 7782 CLARK MANAGER 10 7566 JONES MANAGER 20...6 rows selected.
SQL> SELECT empno, ename, job, deptno 2 FROM emp outr 3 WHERE EXISTS (SELECT empno 4 FROM emp innr 5 WHERE innr.mgr = outr.empno)
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Find all departments that do not have any employees.
Using the NOT EXISTS OperatorUsing the NOT EXISTS Operator
DEPTNO DNAME--------- ---------- 40 OPERATIONS
DEPTNO DNAME--------- ---------- 40 OPERATIONS
SQL> SELECT deptno, dname 2 FROM dept d 3 WHERE NOT EXISTS (SELECT * 4 FROM emp e 5 WHERE d.deptno = e.deptno)
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Correlated UPDATECorrelated UPDATE
Use a correlated subquery to update rows Use a correlated subquery to update rows in one table based on rows from another in one table based on rows from another table.table.
Use a correlated subquery to update rows Use a correlated subquery to update rows in one table based on rows from another in one table based on rows from another table.table.
UPDATE table1 alias1SET column = (SELECT expression FROM table2 alias2 WHERE alias1.column = alias2.column)
UPDATE table1 alias1SET column = (SELECT expression FROM table2 alias2 WHERE alias1.column = alias2.column)
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DELETE FROM table1 alias1 WHERE column operator (SELECT expression FROM table2 alias2 WHERE alias1.column = alias2.column)
DELETE FROM table1 alias1 WHERE column operator (SELECT expression FROM table2 alias2 WHERE alias1.column = alias2.column)
Use a correlated subquery to delete only Use a correlated subquery to delete only those rows that also exist in another those rows that also exist in another table.table.
Use a correlated subquery to delete only Use a correlated subquery to delete only those rows that also exist in another those rows that also exist in another table.table.
Correlated DELETECorrelated DELETE
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SummarySummary
• Correlated subqueries are useful whenever a subquery must return a different result for each candidate row.
• The EXISTS operator is a Boolean operator, testing the presence of a value.
• Correlated subqueries can be used with SELECT, UPDATE, and DELETE statements.
• Correlated subqueries are useful whenever a subquery must return a different result for each candidate row.
• The EXISTS operator is a Boolean operator, testing the presence of a value.
• Correlated subqueries can be used with SELECT, UPDATE, and DELETE statements.
Set OperationsSet Operations
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UNIONUNION
AA BB
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Using the UNION OperatorUsing the UNION OperatorDisplay the name, job title, and department Display the name, job title, and department of all employees.of all employees.Display the name, job title, and department Display the name, job title, and department of all employees.of all employees.
ENAME JOB DEPTNO---------- --------- ---------ADAMS CLERK 30ALLEN SALESMAN 30ALLEN SALESMAN 20BALFORD CLERK 20BLAKE MANAGER 30...20 rows selected.
SQL> SELECT ename, job, deptno 2 FROM emp 3 UNION 4 SELECT name, title, deptid 5 FROM emp_history
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UNION ALLUNION ALL
AA BB
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Using the UNION ALL OperatorUsing the UNION ALL OperatorDisplay the names, employee numbers, and Display the names, employee numbers, and job titles of all employees. job titles of all employees. Display the names, employee numbers, and Display the names, employee numbers, and job titles of all employees. job titles of all employees. SQL> SELECT ename, empno, job 2 FROM emp 3 UNION ALL 4 SELECT name, empid, title 5 FROM emp_history
ENAME EMPNO JOB---------- --------- ---------KING 7839 PRESIDENTBLAKE 7698 MANAGERCLARK 7782 MANAGERCLARK 7782 MANAGERMARTIN 7654 SALESMAN...23 rows selected.
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SET Operator RulesSET Operator Rules• The expressions in the SELECT lists
must match in number and datatype.
• Duplicate rows are automatically eliminated except in UNION ALL.
• Column names from the first query appear in the result.
• The output is sorted in ascending order by default except in UNION ALL.
• Parentheses can be used to alter the sequence of execution.
• The expressions in the SELECT lists must match in number and datatype.
• Duplicate rows are automatically eliminated except in UNION ALL.
• Column names from the first query appear in the result.
• The output is sorted in ascending order by default except in UNION ALL.
• Parentheses can be used to alter the sequence of execution.