Convert subqueries to JOINs : Introduction « Table Joins « Oracle PL/SQL Tutorial

Oracle PL/SQL Tutorial
1. Introduction
2. Query Select
3. Set
4. Insert Update Delete
5. Sequences
6. Table
7. Table Joins
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18. Regular Expressions Functions
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22. PL SQL Statements
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24. PL SQL Programming
25. Cursor
26. Collections
27. Function Procedure Packages
28. Trigger
29. SQL PLUS Session Environment
30. System Tables Data Dictionary
31. System Packages
32. Object Oriented
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34. Large Objects
35. Transaction
36. User Privilege
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Oracle PL/SQL Tutorial » Table Joins » Introduction 
7. 1. 7. Convert subqueries to JOINs
SQL>
SQL> CREATE TABLE emps (
  2    emp varchar(30)
  3   ,title    varchar(30)
  4  );

Table created.

SQL>
SQL> INSERT INTO emps VALUES ('Tom','Programmer');

row created.

SQL> INSERT INTO emps VALUES ('Jack','Tester');

row created.

SQL> INSERT INTO emps VALUES ('Mary','Technician');

row created.

SQL>
SQL> CREATE TABLE JobLevel (
  2    title     varchar(30)
  3   ,rank    varchar(30)
  4  );

Table created.

SQL>
SQL> INSERT INTO JobLevel VALUES ('Programmer','Level1');

row created.

SQL> INSERT INTO JobLevel VALUES ('Tester','Level2');

row created.

SQL> INSERT INTO JobLevel VALUES ('Technician','Level3');

row created.

SQL>
SQL> CREATE TABLE salary (
  2    rank     varchar(30)
  3   ,payment  DECIMAL(10,2)
  4  );

Table created.

SQL>
SQL> INSERT INTO salary VALUES ('Level1',2000.00);

row created.

SQL> INSERT INTO salary VALUES ('Level2',3000.00);

row created.

SQL> INSERT INTO salary VALUES ('Level3',5000.00);

row created.

SQL> INSERT INTO salary VALUES ('Level4',6000.00);

row created.

SQL>
SQL> select from emps;



EMP
------------------------------
TITLE
------------------------------
Tom
Programmer

Jack
Tester

Mary
Technician

rows selected.

SQL> select from JobLevel;



TITLE
------------------------------
RANK
------------------------------
Programmer
Level1

Tester
Level2

Technician
Level3



rows selected.

SQL> select from salary;



RANK                               PAYMENT
------------------------------  ----------
Level1                                2000
Level2                                3000
Level3                                5000
Level4                                6000


rows selected.

SQL>
SQL> SELECT payment FROM salary WHERE rank =
  2    (SELECT rank FROM JobLevel WHERE title =
  3      (SELECT title FROM emps WHERE emp = 'Jack'));



   PAYMENT
----------
      3000

row selected.

SQL>
SQL>
SQL>
SQL> DROP TABLE emps;

Table dropped.

SQL> DROP TABLE JobLevel;

Table dropped.

SQL> DROP TABLE salary;

Table dropped.

SQL>
7. 1. Introduction
7. 1. 1. Performing SELECT Statements that Use More than Two Tables
7. 1. 2. Three different types of joins:
7. 1. 3. Understanding Non-equijoins
7. 1. 4. Performing SELECT Statements that Use Two Tables
7. 1. 5. Example simple join.
7. 1. 6. Use table alias in table join
7. 1. 7. Convert subqueries to JOINs
7. 1. 8. autotrace ansi full outer join
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