curso de java parte 2

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6Copyright 2004, Oracle. All rights reserved.

Using Subqueries to Solve Queries


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6-2 Copyright 2004, Oracle. All rights reserved.

Objectives

After completing this lesson, you should be able to do

the following:

efine subqueries

escribe the types of problems that subqueriescan solve

!ist the types of subqueries

"rite single#row and multiple#row subqueries


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Using a Subquery

to Solve a $roblem

"ho has a salary greater than Abel%s&

"hich employees have salaries greater

than Abel%s salary&

'ain query:

"hat is Abel%s salary&

Subquery:


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(he subquery )inner query* e+ecutes once before

the main query )outer query*

(he result of the subquery is used by the main

query

SELECT select_list

FROM table

WHERE expr operator

(SELECT select_list

FROM table);

Subquery Synta+


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SELECT last_name

FROM employees

WHERE salary >

(SELECT salary

FROM employees WHERE last_name = 'Ael');

Using a Subquery

--...


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/uidelines for Using Subqueries

0nclose subqueries in parentheses

$lace subqueries on the right side of the

comparison condition

(he OR!ER "#clause in the subquery is notneeded unless you are performing (op#1 analysis

Use single#row operators with single#row

subqueries, and use multiple#row operators with

multiple#row subqueries


7/176-7 Copyright 2004, Oracle. All rights reserved.

(ypes of Subqueries

Single#row subquery

'ultiple#row subquery

'ain query

Subquery

returnsS(23!045

S(23!045

SA2'A1

'ain query

Subquery

returns


8/176- Copyright 2004, Oracle. All rights reserved.

Single#4ow Subqueries

4eturn only one row

Use single#row comparison operators

Operator 'eaning

= 0qual to

> /reater than

>= /reater than or equal to

$ !ess than

$= !ess than or equal to

$> 1ot equal to


9/176-! Copyright 2004, Oracle. All rights reserved.

SELECT last_name% &o_% salary

FROM employees

WHERE &o_ =

(SELECT &o_

FROM employees WHERE employee_ = *)

A+! salary >

(SELECT salary

FROM employees

WHERE employee_ = *,);

0+ecuting Single#4ow Subqueries

S(23!045

67..


10/176-"0 Copyright 2004, Oracle. All rights reserved.

SELECT last_name% &o_% salary

FROM employees

WHERE salary =

(SELECT M-+(salary)

FROM employees);

Using /roup 8unctions in a Subquery

69..


11/176-"" Copyright 2004, Oracle. All rights reserved.

SELECT epartment_% M-+(salary)

FROM employees

.RO/0 "# epartment_

HA1-+. M-+(salary) >

(SELECT M-+(salary)

FROM employees

WHERE epartment_ = 23);

(he HA1-+.3lause with Subqueries

(he Oracle server e+ecutes subqueries first

(he Oracle server returns results into the HA1-+.

clause of the main query

69..



SELECT employee_% last_name

FROM employees

WHERE salary =

(SELECT M-+(salary)

FROM employees .RO/0 "# epartment_);

"hat s "rong with (his Statement&

ERROR at lne *4

ORA53*674 sn8le5ro9 s::ery ret:rns more t



SELECT last_name% &o_

FROM employees

WHERE &o_ =

(SELECT &o_

FROM employees WHERE last_name = 'Haas');

"ill (his Statement 4eturn 4ows&

no ro9s selete

Subquery returns no values



'ultiple#4ow Subqueries

4eturn more than one row

Use multiple#row comparison operators

Operator 'eaning

-+ 0qual to any member in the list

A+# 3ompare value to each value returned by the

subquery

ALL 3ompare value to every value returned by the

subquery



SELECT employee_% last_name% &o_% salary

FROM employees

WHERE salary $ A+#

(SELECT salary

FROM employees WHERE &o_ = '-T_0RO.')

A+! &o_ $> '-T_0RO.';

Using theA+#Operator

in 'ultiple#4ow Subqueries

;..., 7...,



SELECT employee_% last_name% &o_% salary

FROM employees

WHERE salary $ ALL

(SELECT salary

FROM employees WHERE &o_ = '-T_0RO.')

A+! &o_ $> '-T_0RO.';

Using theALLOperator

in 'ultiple#4ow Subqueries

;..., 7...,


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SELECT emplast_name

FROM employees emp

WHERE empemployee_ +OT -+

(SELECT m8rmana8er_

FROM employees m8r);

no ro9s selete

1ull >alues in a Subquery

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