劉志俊 (chih-chin liu) 中華大學資訊工程系 october 2001 chap 9 sql (iii): advanced...

劉志俊 (Chih-Chin Liu)

中華大學資訊工程系

October 2001

Chap 9 SQL (III): Advanced Queries

Chap 9 SQL (III): Advanced Queries

Assistant Prof. Chih-Chin Liu

Outline

Joins

Set Operations

Subqueries

Subtotals and GROUP BY

CONNECT BY


Joins

JOIN operations can combine data stored in

more than two tables as a single table.

In SQL-89, join conditions is specified in the

WHERE clauses.

In SQL-92, Join conditions can be specified in

either the FROM or WHERE clauses; specifying

them in the FROM clause is recommended.


Joins

SQL-89 JOIN Syntax

SQL-92 JOIN Syntax (Oracle Do Not Support)

FROM table1INNER JOIN table2ON table1.column = table2.column

FROM table1, table2WHERE table1.column = table2.column


Joins

Joins can be categorized as: Inner joins (the typical join operation, which uses

some comparison operator like = or <>). These

include equi-joins and natural joins.

Outer joins. Outer joins can be a left, right, or full

outer join.

Cross joins return all rows from the left table, each

row from the left table is combined with all rows from

the right table. Cross joins are also called Cartesian

products.


Joins

Example 1: Inner Join


Joins

Example 2: Table Alias (Reflexive Join)


Joins

Example 3: Inequality Join


Joins

Joins can be categorized as: Inner joins (the typical join operation, which uses

some comparison operator like = or <>). These

include equi-joins and natural joins.

Outer joins. Outer joins can be a left, right, or full

outer join.

Cross joins return all rows from the left table, each

row from the left table is combined with all rows from

the right table. Cross joins are also called Cartesian

products.


Joins

Two View Examples


Joins

INNER JOINAnimalID Name

1 Leisha

2 Gene

3 Vivian

AnimalID Category

2 Dog

3 Cat

4 Dog

INNER JOIN

AnimalID Name AnimalID Category

2 Gene 2 Dog

3 Vivian 3 Cat


Joins

Example 4: Inner Join


Joins

LEFT JOINAnimalID Name

1 Leisha

2 Gene

3 Vivian

AnimalID Category

2 Dog

3 Cat

4 Dog

LEFT JOIN


1 Leisha Null Null

2 Gene 2 Dog

3 Vivian 3 Cat


Joins

Example 5: Left Outer Join


Joins

RIGHT JOINAnimalID Name

1 Leisha

2 Gene

3 Vivian

AnimalID Category

2 Dog

3 Cat

4 Dog

RIGHT JOIN


2 Gene 2 Dog

3 Vivian 3 CatNull Null 4 Dog


Joins

Example 6: Right Outer Join


Joins

FULL JOINAnimalID Name

1 Leisha

2 Gene

3 Vivian

AnimalID Category

2 Dog

3 Cat

4 Dog

FULL JOIN


1 Leisha Null Null

2 Gene 2 Dog

3 Vivian 3 CatNull Null 4 Dog


Joins

CROSS JOINAnimalID Name

1 Leisha

2 Gene

3 Vivian

AnimalID Category

2 Dog

3 Cat

4 Dog

CROSS JOIN


1 Leisha 2 Dog

1 Leisha 3 Cat

1 Leisha 4 Dog

2 Gene 2 Dog

2 Gene 3 Cat

2 Gene 4 Dog

3 Vivian 2 Dog

3 Vivian 3 Cat

3 Vivian 4 Dog


Joins

Example 7: Cross Join (Cartesian Products)


Set Operations

A table is a set of tuples.

Set operations can be applied on two

tables.

Set operations: UNION

INTERSECT

MINUS


Set Operations

A B C

T1 UNION T2 A + B + CT1 INTERSECT T2 B

T1 MINUS T2 A

T1 T2


Set Operations

Example 8: UNION


Set Operations

Example 9: INTERSECT


Set Operations

Example 10: MINUS


Subqueries

Which cats sold for more than the average

price of cats ?

Case 1: If we know the average price is $170.

SELECT SaleAnimal.AnimalID, Animal.Category, SaleAnimal.SalePrice

FROM Animal

INNER JOIN SaleAnimal ON Animal.AnimalID = SaleAnimal.AnimalID

WHERE ((Animal.Category = “Cat”) AND (SaleAnimal.SalePrice >170))


Subqueries

Which cats sold for more than the average

price of cats ?

Case 2: If we don’t know the average price.

SQL Query to compute the average price:

SELECT AVG(SalePrice)

FROM Animal


WHERE (Animal.Category = “Cat”)


Subqueries

Combine these two queries:

SELECT SaleAnimal.AnimalID, Animal.Category, SaleAnimal.SalePrice

FROM Animal


WHERE ((Animal.Category = “Cat”) AND (SaleAnimal.SalePrice >

(

SELECT AVG(SalePrice)

FROM Animal


WHERE (Animal.Category = “Cat”)

)))

subquery


Subqueries

The query used for the comparison is defined directly in the internal predicate of the where clause and is known as a nested query.

The query used in the where clause of a nested query is called a subquery.

Some special SQL operators (IN, ALL, ANY, EXISTS) are often used with subqueries.


Subqueries

Example 11: Subquery


Subqueries

Example 12: IN


Subqueries

Example 13: ANY


Subqueries

Example 14: ALL


Subqueries

Example 15: EXISTS


Subqueries

Example 16: NOT EXISTS



GROUP BY specifies the groups into which

output rows are to be placed and, if aggregate

functions are included in the SELECT clause

<select list>, calculates a summary value for

each group.

When a GROUP BY clause is used, each item in

the select list must produce a single value for

each group.



Example 17: GROUP BY



HAVING specifies a search condition for a group

or an aggregate.

HAVING is usually used with the GROUP BY

clause.

When GROUP BY is not used, HAVING

behaves like a WHERE clause.



Example 18: HAVING


CONNECT BY

Example 19: CONNECT BY


DUAL

Example 20: DUAL

劉 志 俊 (chih-chin liu) 中華大學 資訊工程系 october 2001 chap 9 sql (iii): advanced...

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劉志俊 (chih-chin liu) 中華大學資訊工程系 october 2001 chap 9 sql (iii): advanced...