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Transcript of SQL: Part 2 Original materials supplied by the Oracle Academic Initiative (OAI). Edited for...
SQL: Part 2SQL: Part 2
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.
2
OUTLINEOUTLINE
Basic SELECT statementsBasic SELECT statements
Restricting and Sorting DataRestricting and Sorting Data
Using JOINsUsing JOINs
Basic SELECT statementsBasic SELECT statements
Restricting and Sorting DataRestricting and Sorting Data
Using JOINsUsing JOINs
Basic SELECT StatementsBasic SELECT Statements
4
Capabilities of SELECT Statements
Capabilities of SELECT Statements
SelectionSelection ProjectionProjection
Table 1Table 1 Table 2Table 2
Table 1Table 1 Table 1Table 1JoinJoin
5
Basic SELECT StatementBasic SELECT Statement
SELECT [DISTINCT] {*, column [alias],...}FROM table
SELECT [DISTINCT] {*, column [alias],...}FROM table
• SELECT identifies what columns.
• FROM identifies which table.
• SELECT identifies what columns.
• FROM identifies which table.
6
Selecting All ColumnsSelecting All Columns
DEPTNO DNAME LOC--------- -------------- ------------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON
SQL> SELECT * 2 FROM dept
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Selecting Specific ColumnsSelecting Specific Columns
DEPTNO LOC--------- ------------- 10 NEW YORK 20 DALLAS 30 CHICAGO 40 BOSTON
SQL> SELECT deptno, loc 2 FROM dept
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Operator PrecedenceOperator Precedence
• Multiplication and division take priority over addition and subtraction.
• Operators of the same priority are evaluated from left to right.
• Parentheses are used to force prioritized evaluation and to clarify statements.
• Multiplication and division take priority over addition and subtraction.
• Operators of the same priority are evaluated from left to right.
• Parentheses are used to force prioritized evaluation and to clarify statements.
**** //// ++++ ____
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Operator PrecedenceOperator Precedence
SQL> SELECT ename, sal, 12*sal+100 2 FROM emp
ENAME SAL 12*SAL+100---------- --------- ----------KING 5000 60100BLAKE 2850 34300CLARK 2450 29500JONES 2975 35800MARTIN 1250 15100ALLEN 1600 19300...14 rows selected.
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Using ParenthesesUsing Parentheses
SQL> SELECT ename, sal, 12*(sal+100) 2 FROM emp
ENAME SAL 12*(SAL+100)---------- --------- -----------KING 5000 61200BLAKE 2850 35400CLARK 2450 30600JONES 2975 36900MARTIN 1250 16200...14 rows selected.
11
Defining a Null ValueDefining a Null Value• A null is a value that is unavailable,
unassigned, unknown, or inapplicable.
• A null is not the same as zero or a blank space.
• A null is a value that is unavailable, unassigned, unknown, or inapplicable.
• A null is not the same as zero or a blank space.
SQL> SELECT ename, job, comm 2 FROM emp
ENAME JOB COMM---------- --------- ---------KING PRESIDENTBLAKE MANAGER...TURNER SALESMAN 0...14 rows selected.
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Null Values in Arithmetic Expressions
Null Values in Arithmetic Expressions
Arithmetic expressions containing a null Arithmetic expressions containing a null value evaluate to null.value evaluate to null.Arithmetic expressions containing a null Arithmetic expressions containing a null value evaluate to null.value evaluate to null.
SQL> select ename, 12*sal+comm 2 from emp 3 WHERE ename='KING'
ENAME 12*SAL+COMM ---------- -----------KING
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Defining a Column AliasDefining a Column Alias
• Renames a column heading
• Is useful with calculations
• Immediately follows column name; optional AS keyword between column name and alias
• Requires double quotation marks if it contains spaces or special characters or is case sensitive
• Renames a column heading
• Is useful with calculations
• Immediately follows column name; optional AS keyword between column name and alias
• Requires double quotation marks if it contains spaces or special characters or is case sensitive
14
Using Column AliasesUsing Column Aliases
SQL> SELECT ename AS name, sal salary 2 FROM emp
NAME SALARY
------------- ---------
...
SQL> SELECT ename "Name", 2 sal*12 "Annual Salary" 3 FROM emp
Name Annual Salary
------------- -------------
...
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Literal Character StringsLiteral Character Strings
• A literal is a character, expression, or number included in the SELECT list.
• Date and character literal values must be enclosed within single quotation marks.
• Each character string is output once for each row returned.
• A literal is a character, expression, or number included in the SELECT list.
• Date and character literal values must be enclosed within single quotation marks.
• Each character string is output once for each row returned.
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Duplicate RowsDuplicate Rows
The default display of queries is all rows, The default display of queries is all rows, including duplicate rows.including duplicate rows.The default display of queries is all rows, The default display of queries is all rows, including duplicate rows.including duplicate rows.
SQL> SELECT deptno 2 FROM emp
SQL> SELECT deptno 2 FROM emp
DEPTNO--------- 10 30 10 20...14 rows selected.
17
Eliminating Duplicate RowsEliminating Duplicate Rows
Eliminate duplicate rows by using the Eliminate duplicate rows by using the DISTINCT keyword in the SELECT clause.DISTINCT keyword in the SELECT clause.
SQL> SELECT DISTINCT deptno 2 FROM emp
DEPTNO--------- 10 20 30
Restricting and Sorting DataRestricting and Sorting Data
19
Limiting Rows Using a SelectionLimiting Rows Using a Selection
"…retrieve all"…retrieve allemployeesemployees
in department 10"in department 10"
EMPEMP
EMPNO ENAME JOB ... DEPTNO
7839 KING PRESIDENT 10 7698 BLAKE MANAGER 30 7782 CLARK MANAGER 10 7566 JONES MANAGER 20 ...
EMPEMP
EMPNO ENAME JOB ... DEPTNO
7839 KING PRESIDENT 10 7782 CLARK MANAGER 10 7934 MILLER CLERK 10
20
Limiting Rows SelectedLimiting Rows Selected
• Restrict the rows returned by using the WHERE clause.
• The WHERE clause follows the FROM clause.
• Restrict the rows returned by using the WHERE clause.
• The WHERE clause follows the FROM clause.
SELECT [DISTINCT] {*| column [alias], ...}FROM table[WHERE condition(s)]
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Using the WHERE ClauseUsing the WHERE Clause
SQL> SELECT ename, job, deptno 2 FROM emp 3 WHERE job='CLERK'
ENAME JOB DEPTNO---------- --------- ---------JAMES CLERK 30SMITH CLERK 20ADAMS CLERK 20MILLER CLERK 10
22
Character Strings and DatesCharacter Strings and Dates
• Character strings and date values are enclosed in single quotation marks.
• Character values are case sensitive and date values are format sensitive.
• The default date format is DD-MON-YY.
• Character strings and date values are enclosed in single quotation marks.
• Character values are case sensitive and date values are format sensitive.
• The default date format is DD-MON-YY.
SQL> SELECT ename, job, deptno 2 FROM emp 3 WHERE ename = 'JAMES'
SQL> SELECT ename, job, deptno 2 FROM emp 3 WHERE ename = 'JAMES'
23
Comparison OperatorsComparison Operators
Operator
=
>
>=
<
<=
<>
Meaning
Equal to
Greater than
Greater than or equal to
Less than
Less than or equal to
Not equal to
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Using the Comparison Operators
Using the Comparison Operators
SQL> SELECT ename, sal, comm 2 FROM emp 3 WHERE sal<=comm
ENAME SAL COMM---------- --------- ---------MARTIN 1250 1400
25
Other Comparison OperatorsOther Comparison Operators
Operator
BETWEEN
...AND...
IN(list)
LIKE
IS NULL
Meaning
Between two values (inclusive)
Match any of a list of values
Match a character pattern
Is a null value
26
Using the BETWEEN OperatorUsing the BETWEEN Operator
ENAME SAL---------- ---------MARTIN 1250TURNER 1500WARD 1250ADAMS 1100MILLER 1300
SQL> SELECT ename, sal 2 FROM emp 3 WHERE sal BETWEEN 1000 AND 1500
Lowerlimit
Higherlimit
Use the BETWEEN operator to display Use the BETWEEN operator to display rows based on a range of values.rows based on a range of values.Use the BETWEEN operator to display Use the BETWEEN operator to display rows based on a range of values.rows based on a range of values.
27
Using the IN OperatorUsing the IN Operator
Use the IN operator to test for values in a Use the IN operator to test for values in a list.list.Use the IN operator to test for values in a Use the IN operator to test for values in a list.list.
SQL> SELECT empno, ename, sal, mgr 2 FROM emp 3 WHERE mgr IN (7902, 7566, 7788)
EMPNO ENAME SAL MGR--------- ---------- --------- --------- 7902 FORD 3000 7566 7369 SMITH 800 7902 7788 SCOTT 3000 7566 7876 ADAMS 1100 7788
28
Using the LIKE OperatorUsing the LIKE Operator
• Use the LIKE operator to perform wildcard searches of valid search string values.
• Search conditions can contain either literal characters or numbers.
– % denotes zero or many characters.
– _ denotes one character.
• Use the LIKE operator to perform wildcard searches of valid search string values.
• Search conditions can contain either literal characters or numbers.
– % denotes zero or many characters.
– _ denotes one character.
SQL> SELECT ename 2 FROM emp 3 WHERE ename LIKE 'S%'
29
Using the LIKE OperatorUsing the LIKE Operator
• You can combine pattern-matching characters.• You can combine pattern-matching
characters.
SQL> SELECT ename 2 FROM emp 3 WHERE ename LIKE '_A%'
ENAME---------- MARTINJAMES WARD
30
Using the IS NULL OperatorUsing the IS NULL Operator
Test for null values with the IS NULL Test for null values with the IS NULL operator.operator.Test for null values with the IS NULL Test for null values with the IS NULL operator.operator.
SQL> SELECT ename, mgr 2 FROM emp 3 WHERE mgr IS NULL
ENAME MGR---------- ---------KING
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Logical OperatorsLogical Operators
Operator
AND
OR
NOT
Meaning
Returns TRUE if both component
conditions are TRUE
Returns TRUE if either component
condition is TRUE
Returns TRUE if the following condition is FALSE
32
Using the AND OperatorUsing the AND Operator
AND requires both conditions to be TRUE.AND requires both conditions to be TRUE.
SQL> SELECT empno, ename, job, sal 2 FROM emp 3 WHERE sal>=1100 4 AND job='CLERK'
EMPNO ENAME JOB SAL--------- ---------- --------- --------- 7876 ADAMS CLERK 1100 7934 MILLER CLERK 1300
33
Using the OR OperatorUsing the OR Operator
OR requires either condition to be TRUE.OR requires either condition to be TRUE.OR requires either condition to be TRUE.OR requires either condition to be TRUE.SQL> SELECT empno, ename, job, sal 2 FROM emp 3 WHERE sal>=1100 4 OR job='CLERK'
EMPNO ENAME JOB SAL--------- ---------- --------- --------- 7839 KING PRESIDENT 5000 7698 BLAKE MANAGER 2850 7782 CLARK MANAGER 2450 7566 JONES MANAGER 2975 7654 MARTIN SALESMAN 1250 ... 7900 JAMES CLERK 950 ...14 rows selected.
34
Using the NOT OperatorUsing the NOT Operator
SQL> SELECT ename, job 2 FROM emp 3 WHERE job NOT IN ('CLERK','MANAGER','ANALYST')
ENAME JOB---------- ---------KING PRESIDENTMARTIN SALESMANALLEN SALESMANTURNER SALESMANWARD SALESMAN
35
Rules of PrecedenceRules of Precedence
Override rules of precedence by using Override rules of precedence by using parentheses.parentheses.Override rules of precedence by using Override rules of precedence by using parentheses.parentheses.
Order Evaluated Operator
1 All comparison operators
2 NOT
3 AND
4 OR
36
ORDER BY ClauseORDER BY Clause• Sort rows with the ORDER BY clause– ASC: ascending order, default– DESC: descending order
• The ORDER BY clause comes last in the SELECT statement.
• Sort rows with the ORDER BY clause– ASC: ascending order, default– DESC: descending order
• The ORDER BY clause comes last in the SELECT statement.
SQL> SELECT ename, job, deptno, hiredate 2 FROM emp 3 ORDER BY hiredate
ENAME JOB DEPTNO HIREDATE---------- --------- --------- ---------SMITH CLERK 20 17-DEC-80ALLEN SALESMAN 30 20-FEB-81...14 rows selected.
37
Sorting in Descending OrderSorting in Descending Order
SQL> SELECT ename, job, deptno, hiredate 2 FROM emp 3 ORDER BY hiredate DESC
ENAME JOB DEPTNO HIREDATE---------- --------- --------- ---------ADAMS CLERK 20 12-JAN-83SCOTT ANALYST 20 09-DEC-82MILLER CLERK 10 23-JAN-82JAMES CLERK 30 03-DEC-81FORD ANALYST 20 03-DEC-81KING PRESIDENT 10 17-NOV-81MARTIN SALESMAN 30 28-SEP-81...14 rows selected.
38
Sorting by Column AliasSorting by Column Alias
SQL> SELECT empno, ename, sal*12 annsal 2 FROM emp 3 ORDER BY annsal
EMPNO ENAME ANNSAL--------- ---------- --------- 7369 SMITH 9600 7900 JAMES 11400 7876 ADAMS 13200 7654 MARTIN 15000 7521 WARD 15000 7934 MILLER 15600 7844 TURNER 18000...14 rows selected.
39
Sorting by Multiple ColumnsSorting by Multiple Columns
• The order of the ORDER BY list is used to sort the results of the query.• The order of the ORDER BY list is used to sort
the results of the query.
• A column not in the SELECT list can be used to sort the query results.• A column not in the SELECT list can be used to
sort the query results.
SQL> SELECT ename, deptno, sal 2 FROM emp 3 ORDER BY deptno, sal DESC
ENAME DEPTNO SAL---------- --------- ---------KING 10 5000CLARK 10 2450MILLER 10 1300FORD 20 3000...14 rows selected.
Using JOINs Using JOINs
41
EMPNO DEPTNO LOC----- ------- -------- 7839 10 NEW YORK 7698 30 CHICAGO 7782 10 NEW YORK 7566 20 DALLAS 7654 30 CHICAGO 7499 30 CHICAGO...14 rows selected.
EMPNO DEPTNO LOC----- ------- -------- 7839 10 NEW YORK 7698 30 CHICAGO 7782 10 NEW YORK 7566 20 DALLAS 7654 30 CHICAGO 7499 30 CHICAGO...14 rows selected.
Obtaining Data from Multiple TablesObtaining Data from Multiple TablesEMP EMP DEPT DEPT EMPNO ENAME ... DEPTNO------ ----- ... ------ 7839 KING ... 10 7698 BLAKE ... 30 ... 7934 MILLER ... 10
DEPTNO DNAME LOC ------ ---------- -------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON
42
What Is a Join?What Is a Join?
Use a join to query data from more than Use a join to query data from more than one table.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 Use a join to query data from more than one table.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.
SELECT table1.column, table2.columnFROM table1, table2WHERE table1.column1 = table2.column2
SELECT table1.column, table2.columnFROM table1, table2WHERE table1.column1 = table2.column2
43
Cartesian ProductCartesian Product
• A Cartesian product is formed when:
– A join condition is omitted
– A join condition is invalid
– All rows in the first table are joined to all rows in the second table
• To avoid a Cartesian product, always include a valid join condition in a WHERE clause.
• A Cartesian product is formed when:
– A join condition is omitted
– A join condition is invalid
– All rows in the first table are joined to all rows in the second table
• To avoid a Cartesian product, always include a valid join condition in a WHERE clause.
44
Generating a Cartesian ProductGenerating a Cartesian Product
ENAME DNAME------ ----------KING ACCOUNTINGBLAKE ACCOUNTING ...KING RESEARCHBLAKE RESEARCH...56 rows selected.
ENAME DNAME------ ----------KING ACCOUNTINGBLAKE ACCOUNTING ...KING RESEARCHBLAKE RESEARCH...56 rows selected.
EMP (14 rows) EMP (14 rows) DEPT (4 rows) DEPT (4 rows)
EMPNO ENAME ... DEPTNO------ ----- ... ------ 7839 KING ... 10 7698 BLAKE ... 30 ... 7934 MILLER ... 10
EMPNO ENAME ... DEPTNO------ ----- ... ------ 7839 KING ... 10 7698 BLAKE ... 30 ... 7934 MILLER ... 10
DEPTNO DNAME LOC ------ ---------- -------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON
DEPTNO DNAME LOC ------ ---------- -------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON
““CartesianCartesianproduct: product:
14*4=56 rows”14*4=56 rows”
45
Types of JoinsTypes of Joins
EquijoinEquijoin Non-equijoinNon-equijoin Outer joinOuter join Self joinSelf join
46
What Is an Equijoin?What Is an Equijoin?EMP EMP DEPT DEPT EMPNO ENAME DEPTNO------ ------- ------- 7839 KING 10 7698 BLAKE 30 7782 CLARK 10 7566 JONES 20 7654 MARTIN 30 7499 ALLEN 30 7844 TURNER 30 7900 JAMES 30 7521 WARD 30 7902 FORD 20 7369 SMITH 20...14 rows selected.
DEPTNO DNAME LOC ------- ---------- -------- 10 ACCOUNTING NEW YORK 30 SALES CHICAGO 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 30 SALES CHICAGO 30 SALES CHICAGO 30 SALES CHICAGO 30 SALES CHICAGO 20 RESEARCH DALLAS 20 RESEARCH DALLAS...14 rows selected.
Foreign keyForeign key Primary keyPrimary key
47
Retrieving Records with Equijoins
Retrieving Records with Equijoins
SQL> SELECT emp.empno, emp.ename, emp.deptno, 2 dept.deptno, dept.loc 3 FROM emp, dept 4 WHERE emp.deptno=dept.deptno
EMPNO ENAME DEPTNO DEPTNO LOC----- ------ ------ ------ --------- 7839 KING 10 10 NEW YORK 7698 BLAKE 30 30 CHICAGO 7782 CLARK 10 10 NEW YORK 7566 JONES 20 20 DALLAS...14 rows selected.
48
Qualifying Ambiguous Column Names
Qualifying Ambiguous Column Names
• Use table prefixes to qualify column names that are in multiple tables.
• Improve performance by using table prefixes.
• Distinguish columns that have identical names but reside in different tables by using column aliases.
• Use table prefixes to qualify column names that are in multiple tables.
• Improve performance by using table prefixes.
• Distinguish columns that have identical names but reside in different tables by using column aliases.
49
Additional Search ConditionsUsing the AND Operator
Additional Search ConditionsUsing the AND Operator
EMP EMP DEPT DEPT EMPNO ENAME DEPTNO------ ------- ------- 7839 KING 10 7698 BLAKE 30 7782 CLARK 10 7566 JONES 20 7654 MARTIN 30 7499 ALLEN 30 7844 TURNER 30 7900 JAMES 30 7521 WARD 30 7902 FORD 20 7369 SMITH 20...14 rows selected.
DEPTNO DNAME LOC ------ --------- -------- 10 ACCOUNTING NEW YORK 30 SALES CHICAGO 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 30 SALES CHICAGO 30 SALES CHICAGO 30 SALES CHICAGO 30 SALES CHICAGO 20 RESEARCH DALLAS 20 RESEARCH DALLAS...14 rows selected.
50
Using Table AliasesUsing Table Aliases
Simplify queries by using table aliases.Simplify queries by using table aliases.Simplify queries by 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;
51
Joining More Than Two TablesJoining More Than Two Tables
NAME CUSTID----------- ------JOCKSPORTS 100TKB SPORT SHOP 101VOLLYRITE 102JUST TENNIS 103K+T SPORTS 105SHAPE UP 106WOMENS SPORTS 107... ...9 rows selected.
NAME CUSTID----------- ------JOCKSPORTS 100TKB SPORT SHOP 101VOLLYRITE 102JUST TENNIS 103K+T SPORTS 105SHAPE UP 106WOMENS SPORTS 107... ...9 rows selected.
CUSTOMER CUSTOMER
CUSTID ORDID------- ------- 101 610 102 611 104 612 106 601 102 602 106 604 106 605... 21 rows selected.
CUSTID ORDID------- ------- 101 610 102 611 104 612 106 601 102 602 106 604 106 605... 21 rows selected.
ORD ORD
ORDID ITEMID------ ------- 610 3 611 1 612 1 601 1 602 1...64 rows selected.
ORDID ITEMID------ ------- 610 3 611 1 612 1 601 1 602 1...64 rows selected.
ITEM ITEM
52
Non-EquijoinsNon-EquijoinsEMPEMP SALGRADESALGRADE
““salary in the EMP salary in the EMP table is between table is between low salary and high low salary and high salary in the SALGRADEsalary in the SALGRADEtable”table”
EMPNO ENAME SAL------ ------- ------ 7839 KING 5000 7698 BLAKE 2850 7782 CLARK 2450 7566 JONES 2975 7654 MARTIN 1250 7499 ALLEN 1600 7844 TURNER 1500 7900 JAMES 950...14 rows selected.
GRADE LOSAL HISAL----- ----- ------1 700 12002 1201 14003 1401 20004 2001 30005 3001 9999
53
Retrieving Records with Non-Equijoins
Retrieving Records with Non-Equijoins
ENAME SAL GRADE---------- --------- ---------JAMES 950 1SMITH 800 1ADAMS 1100 1...14 rows selected.
SQL> SELECT e.ename, e.sal, s.grade
2 FROM emp e, salgrade s
3 WHERE e.sal
4 BETWEEN s.losal AND s.hisal
54
Outer JoinsOuter Joins
EMP EMP DEPT DEPT
No employee in theNo employee in theOPERATIONS departmentOPERATIONS department
ENAME DEPTNO----- ------KING 10BLAKE 30CLARK 10JONES 20...
DEPTNO DNAME------ ----------10 ACCOUNTING30 SALES10 ACCOUNTING20 RESEARCH...40 OPERATIONS
55
Outer JoinsOuter Joins
• You use an outer join to also see rows that do not usually meet the join condition
• Outer join operator is the asterisk (*)
• You use an outer join to also see rows that do not usually meet the join condition
• Outer join operator is the asterisk (*)
SELECT table1.column, table2.column
FROM table1, table2
WHERE table1.column* = table2.column
SELECT table1.column, table2.column
FROM table1, table2
WHERE table1.column* = table2.column
SELECT table1.column, table2.column
FROM table1, table2
WHERE table1.column = table2.column*
SELECT table1.column, table2.column
FROM table1, table2
WHERE table1.column = table2.column*
56
Using Outer JoinsUsing Outer Joins
SQL> SELECT e.ename, d.deptno, d.dname
2 FROM emp e, dept d
3 WHERE e.deptno* = d.deptno
4 ORDER BY e.deptno
ENAME DEPTNO DNAME---------- --------- -------------KING 10 ACCOUNTINGCLARK 10 ACCOUNTING... 40 OPERATIONS15 rows selected.
57
Self JoinsSelf Joins
EMP (WORKER)EMP (WORKER) EMP (MANAGER)EMP (MANAGER)
““MGR in the WORKER table is equal to EMPNO in the MGR in the WORKER table is equal to EMPNO in the MANAGER table”MANAGER table”
EMPNO ENAME MGR----- ------ ---- 7839 KING 7698 BLAKE 7839 7782 CLARK 7839 7566 JONES 7839 7654 MARTIN 7698 7499 ALLEN 7698
EMPNO ENAME----- --------
7839 KING 7839 KING 7839 KING 7698 BLAKE 7698 BLAKE
58
Joining a Table to ItselfJoining a Table to Itself
WORKER.ENAME WORKS FOR MANAGER.ENAME------------------------------------BLAKE works for KINGCLARK works for KINGJONES works for KINGMARTIN works for BLAKE...13 rows selected.
WORKER.ENAME WORKS FOR MANAGER.ENAME------------------------------------BLAKE works for KINGCLARK works for KINGJONES works for KINGMARTIN works for BLAKE...13 rows selected.
SQL> SELECT worker.ename +' works for '+ manager.ename
2 FROM emp worker, emp manager
3 WHERE worker.mgr = manager.empno