SQL VISUAL QUICKSTART GUIDE- P24 ppsx

✔ Tip ■ Using WHERE syntax, Listing 7.7 is equiva-lent to: SELECT a.au_id, a.au_fname, a.au_lname, ta.title_id FROM authors a, title_authors ta WHERE a.au_id = ta.au_id ORDER BY a.au_id

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Creating an Inner Join

An inner join:

◆ Uses a comparison operator ( = , <> , < , <= ,

> , or >= ) to match rows from two tables

based on the values in common columns

from each table You can retrieve all rows

in which the author identifier (the column

au_id ) is the same in both the tables

authors and title_authors , for example.

◆ Returns a result that contains only joined

rows that satisfy the join condition(s).

◆ Is the most common type of join.

To create an inner join:

◆ Type:

SELECT columns

FROM table1

INNER JOIN table2

ON join_conditions

columns is one or more comma-separated

expressions or column names from table1

or table2 table1 and table2 are the names

of the joined tables If the tables have

some column names in common, qualify

those column names with the names of

the tables.

join_conditions specifies one or more

join conditions to be evaluated for each

pair of joined rows A join condition

takes this form:

[table1.]column op [table2.]column

op usually is = but can be any compari-son operator: = , <> , < , <= , > , or >= (refer

to Table 4.2 in Chapter 4) You can com-bine multiple join conditions with AND

or OR ; see “Combining and Negating Conditions with AND, OR, and NOT ” in Chapter 4.

✔ Tips

■ To create an inner join of three or more tables by using JOIN syntax, type:

SELECT columns FROM table1 INNER JOIN table2

ON join_condition1 INNER JOIN table3

ON join_condition2

Using WHERE syntax, type:

SELECT columns FROM table1, table2,

WHERE join_condition1 AND join_condition2

■ If you’re using WHERE syntax and you omit a join condition accidentally, you’ll create a cross join If the affected tables are large production tables, you’ll have a

“runaway query” that you might have to ask your database administrator to kill.

■ By default, JOIN (without CROSS , NATURAL , OUTER , or any other modifiers) is equiva-lent to INNER JOIN

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■ You can use WHERE syntax or

JOIN syntax in Microsoft

joins that involve three or more tables, Access requires you to nest joins by using the following general syntax:

SELECT columns FROM table1 INNER JOIN (table2 INNER JOIN (table3 INNER JOIN (table4

INNER JOIN )

ON table3.column3 op table4.column4)

ON table2.column2 op table3.column3)

ON table1.column1 op table2.column2;

(Other DBMSs also let you nest joins by using parentheses, but Access requires it.)

use WHERE joins instead Oracle 9i and

later support JOIN syntax.

Listing 7.7 joins two tables on the column

au_id to list the books that each author wrote (or cowrote) Each author’s au_id in the table authors matches zero or more rows

in the table title_authors See Figure 7.7

for the result Note that author A07 (Paddy O’Furniture) is omitted from the result because he has written no books and so has

no matching rows in title_authors

✔ Tip

■ Using WHERE syntax, Listing 7.7 is equiva-lent to:

SELECT a.au_id, a.au_fname, a.au_lname, ta.title_id FROM authors a, title_authors ta WHERE a.au_id = ta.au_id

ORDER BY a.au_id ASC, ta.title_id ASC;

Listing 7.7 List the books that each author wrote (or

cowrote) See Figure 7.7 for the result.

SELECT

a.au_id,

a.au_fname,

a.au_lname,

ta.title_id

FROM authors a

INNER JOIN title_authors ta

ON a.au_id = ta.au_id

ORDER BY a.au_id ASC, ta.title_id ASC;

Listing

au_id au_fname au_lname title_id

- - -

-A01 Sarah Buchman T01

A01 Sarah Buchman T02

A01 Sarah Buchman T13

A02 Wendy Heydemark T06

A03 Hallie Hull T04

A03 Hallie Hull T11

A04 Klee Hull T04

A04 Klee Hull T05

A04 Klee Hull T07

A04 Klee Hull T11

A05 Christian Kells T03

A06 Kellsey T08

A06 Kellsey T09

A06 Kellsey T11

Figure 7.7 Result of Listing 7.7.

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Listing 7.8 joins two tables on the column

pub_id to list each book’s title name and ID,

and each book’s publisher name and ID.

Note that the join is necessary to retrieve

only the publisher name (the fourth column

in the result); all the other three columns are

available in the table titles See Figure 7.8

for the result.

✔ Tip

■ Using WHERE syntax, Listing 7.8 is

equiva-lent to:

SELECT t.title_id, t.title_name,

t.pub_id, p.pub_name

FROM titles t, publishers p

WHERE p.pub_id = t.pub_id

ORDER BY t.title_name ASC;

Listing 7.8 List each book’s title name and ID and

each book’s publisher name and ID See Figure 7.8 for the result.

SELECT t.title_id, t.title_name, t.pub_id, p.pub_name

FROM titles t INNER JOIN publishers p

ON p.pub_id = t.pub_id

ORDER BY t.title_name ASC;

Listing

title_id title_name pub_id pub_name

- - -

-T01 1977! P01 Abatis Publishers

T02 200 Years of German Humor P03 Schadenfreude Press

T03 Ask Your System Administrator P02 Core Dump Books

T04 But I Did It Unconsciously P04 Tenterhooks Press

T05 Exchange of Platitudes P04 Tenterhooks Press

T06 How About Never? P01 Abatis Publishers

T07 I Blame My Mother P03 Schadenfreude Press

T08 Just Wait Until After School P04 Tenterhooks Press

T09 Kiss My Boo-Boo P04 Tenterhooks Press

T10 Not Without My Faberge Egg P01 Abatis Publishers

T11 Perhaps It's a Glandular Problem P04 Tenterhooks Press

T12 Spontaneous, Not Annoying P01 Abatis Publishers

T13 What Are The Civilian Applications? P03 Schadenfreude Press

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Listing 7.9 uses two join conditions to list

the authors who live in the same city and state as some publisher (any publisher) See

Figure 7.9 for the result Note that this

query is a natural join on the identically named, nonkey columns city and state in the two tables (see “Creating a Natural Join with NATURAL JOIN ” earlier in this chapter).

An equivalent query is:

SELECT a.au_id, a.au_fname, a.au_lname, a.city, a.state FROM authors a

NATURAL JOIN publishers p ORDER BY a.au_id ASC;

✔ Tip

■ Using WHERE syntax, Listing 7.9 is equiva-lent to:

SELECT a.au_id, a.au_fname, a.au_lname, a.city, a.state FROM authors a, publishers p WHERE a.city = p.city AND a.state = p.state ORDER BY a.au_id ASC;

Listing 7.9 List the authors who live in the same

city and state in which a publisher is located See

Figure 7.9 for the result.

SELECT

a.au_id,

a.au_fname,

a.au_lname,

a.city,

a.state

FROM authors a

INNER JOIN publishers p

ON a.city = p.city

AND a.state = p.state

ORDER BY a.au_id;

Listing

au_id au_fname au_lname city state

- -

-A03 Hallie Hull San Francisco CA

A04 Klee Hull San Francisco CA

A05 Christian Kells New York NY

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Listing 7.10 combines an inner join with

WHERE conditions to list books published in

California or outside the large North American

countries; see “Filtering Rows with WHERE ” in

Chapter 4 See Figure 7.10 for the result.

✔ Tip

equiv-alent to:

p.state, p.country

FROM titles t, publishers p

WHERE t.pub_id = p.pub_id

AND (p.state = ‘CA’

OR p.country NOT IN

(‘USA’, ‘Canada’, ‘Mexico’)) ORDER BY t.title_id ASC;

Listing 7.10 List the books published in California or

outside the large North American countries See Figure 7.10 for the result.

SELECT t.title_id, t.title_name, p.state, p.country

FROM titles t INNER JOIN publishers p

ON t.pub_id = p.pub_id

WHERE p.state = 'CA'

OR p.country NOT IN ('USA', 'Canada', 'Mexico')

ORDER BY t.title_id ASC;

Listing

title_id title_name state country

- -

-T02 200 Years of German Humor NULL Germany

T03 Ask Your System Administrator CA USA

T04 But I Did It Unconsciously CA USA

T05 Exchange of Platitudes CA USA

T07 I Blame My Mother NULL Germany

T08 Just Wait Until After School CA USA

T09 Kiss My Boo-Boo CA USA

T11 Perhaps It's a Glandular Problem CA USA

T13 What Are The Civilian Applications? NULL Germany

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Listing 7.11 combines an inner join with

the aggregate function COUNT() and a GROUP

BY clause to list the number of books that each author wrote (or cowrote) For infor-mation about aggregate functions and GROUP

BY , see Chapter 6 See Figure 7.11 for the

result Note that, as in Figure 7.7, author A07 (Paddy O’Furniture) is omitted from the result because he has written no books and

so has no matching rows in title_authors See Listing 7.30 in “Creating Outer Joins with OUTER JOIN ” later in this chapter for an example that lists authors who have written

no books.

✔ Tip

■ Using WHERE syntax, Listing 7.11 is equiv-alent to:

SELECT a.au_id, COUNT(ta.title_id)

AS “Num books”

FROM authors a, title_authors ta WHERE a.au_id = ta.au_id

GROUP BY a.au_id ORDER BY a.au_id ASC;

Listing 7.11 List the number of books that each author

wrote (or cowrote) See Figure 7.11 for the result.

SELECT

a.au_id,

COUNT(ta.title_id) AS "Num books"

FROM authors a

GROUP BY a.au_id

ORDER BY a.au_id ASC;

Listing

au_id Num books

-

-A01 3

A02 4

A03 2

A04 4

A05 1

A06 3

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Listing 7.12 uses WHERE conditions to list

the advance paid for each biography See

Figure 7.12 for the result.

✔ Tip

equiv-alent to:

r.advance

FROM royalties r, titles t

WHERE r.title_id = t.title_id

AND t.type = ‘biography’

AND r.advance IS NOT NULL

ORDER BY r.advance DESC;

Listing 7.12 List the advance paid for each biography.

See Figure 7.12 for the result.

SELECT t.title_id, t.title_name, r.advance

FROM royalties r INNER JOIN titles t

ON r.title_id = t.title_id

WHERE t.type = 'biography' AND r.advance IS NOT NULL ORDER BY r.advance DESC;

Listing

title_id title_name advance - - -T07 I Blame My Mother 1000000.00 T12 Spontaneous, Not Annoying 50000.00 T06 How About Never? 20000.00

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Listing 7.13 uses aggregate functions and a

GROUP BY clause to list the count and total advance paid for each type of book See

✔ Tip

SELECT t.type, COUNT(r.advance)

AS “COUNT(r.advance)”, SUM(r.advance)

AS “SUM(r.advance)”

FROM royalties r, titles t WHERE r.title_id = t.title_id AND r.advance IS NOT NULL GROUP BY t.type

ORDER BY t.type ASC;

Listing 7.13 List the count and total advance paid for

each type of book See Figure 7.13 for the result.

SELECT

t.type,

COUNT(r.advance)

AS "COUNT(r.advance)",

SUM(r.advance)

AS "SUM(r.advance)"

FROM royalties r

INNER JOIN titles t

WHERE r.advance IS NOT NULL

GROUP BY t.type

ORDER BY t.type ASC;

Listing

type COUNT(r.advance) SUM(r.advance)

-

-biography 3 1070000.00

children 2 0.00

computer 1 15000.00

history 3 31000.00

psychology 3 220000.00

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Listing 7.14 is similar to Listing 7.13,

except that it uses an additional grouping

column to list the count and total advance

paid for each type of book by publisher See

✔ Tip

equiv-alent to:

SELECT t.type, t.pub_id,

COUNT(r.advance)

AS “COUNT(r.advance)”, SUM(r.advance)

AS “SUM(r.advance)”

FROM royalties r, titles t

WHERE r.title_id = t.title_id

AND r.advance IS NOT NULL

GROUP BY t.type, t.pub_id

ORDER BY t.type ASC, t.pub_id ASC;

Listing 7.14 List the count and total advance paid for

each type of book, by publisher See Figure 7.14 for the result.

SELECT t.type, t.pub_id, COUNT(r.advance) AS "COUNT(r.advance)", SUM(r.advance) AS "SUM(r.advance)"

FROM royalties r INNER JOIN titles t

WHERE r.advance IS NOT NULL GROUP BY t.type, t.pub_id ORDER BY t.type ASC, t.pub_id ASC;

Listing

type pub_id COUNT(r.advance) SUM(r.advance)

- -

-biography P01 2 70000.00

biography P03 1 1000000.00

children P04 2 0.00

computer P02 1 15000.00

history P01 1 10000.00

history P03 2 21000.00

psychology P04 3 220000.00

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Listing 7.15 uses a HAVING clause to list the number of coauthors of each book written

by two or more authors For information about HAVING , see “Filtering Groups with HAVING ” in Chapter 6 See Figure 7.15 for

the result.

✔ Tip

SELECT ta.title_id, COUNT(ta.au_id) AS “Num authors”

FROM authors a, title_authors ta WHERE a.au_id = ta.au_id

GROUP BY ta.title_id HAVING COUNT(ta.au_id) > 1 ORDER BY ta.title_id ASC;

Listing 7.15 List the number of coauthors of each

book written by two or more authors See Figure 7.15

for the result.

SELECT

ta.title_id,

COUNT(ta.au_id) AS "Num authors"

FROM authors a

GROUP BY ta.title_id

HAVING COUNT(ta.au_id) > 1

ORDER BY ta.title_id ASC;

Listing

title_id Num authors

-

-T04 2

T07 2

T11 3

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