sql (structured query language) - journey never ends · n bahasa untuk memanggil fungsi-fungsi...

©Silberschatz, Korth and Sudarshan4.1Database System Concepts

SQL (Structured Query Language)SQL (Structured Query Language)Source:Source: SilbershatzSilbershatz, Fanny , Fanny Santosa dan Aniati MurniSantosa dan Aniati Murni

n Concepts of Query

n Basic Structure

n Set Operations

n Aggregate Functions

n Null Values

n Nested Subqueries

n Derived Relations

n Views

n Modification of the Database

n Joined Relations


TujuanTujuan

n Menjelaskan bahasa formal yang digunakan pada basis data relasional

n Menjelaskan SQL sebagai bahasa yang standar

n Memberikan beberapa contoh teknik pembuatan query dengan menggunakan SQL


Pengertian Pengertian QueryQuery

nQuery adalah perintah-perintah untuk mengakses data pada sistem basis data


SQL (1)SQL (1)

n SQL adalah bahasa query baku untuk DBMS

n SQL diambil sebagai bakuan sejak tahun 1992

n Awalnya diterapkan pada DBMS besar seperti Oracle dan Informix, sekarang juga pada DBMS berbasis PC seperti dBASE dan FoxPro.

n SQL bersifat sebagai bahasa tingkat tinggi (high level). Pemakai hanya menyebutkan hasil yang diinginkan dan optimasi pelaksanaan query dilakukan oleh DBMS.

n Satu perintah SQL dapat mewakili puluhan baris perintah bahasa xBASE.


SQL (2)SQL (2)

n SQL dapat disisipkan ke bahasa pemrograman yang lain seperti C, Pascal, Cobol, dll.

n Bahasa SQL terbagi dalam dua bagian besar, yaitu: DDL (Data Definition Language) dan DML (Data Manipulation Language)

n DDL mendefinisikan struktur basis data, seperti pembuatan basis data, pembuatan tabel dsbnya. Contoh: CREATE DATABASE dan CREATE TABLE.

n DML merupakan bagian untuk memanipulasi basis data seperti: pengaksesan data, penghapusan, penambahan dan pengubahan data. DML juga dapat digunakan untuk melakukan komputasi data. Contoh: INSERT, DELETE, dan UPDATE.


DDL (1)DDL (1)

n Perintah SQL untuk definisi data:

H CREATE untuk membentuk basis data, taable atau index

H ALTER untuk mengubah struktur table

H DROP untuk menghapus basis data, table atau index

n CREATE DATABASE

H Untuk membentuk basis data

H Sintaks: CREATE DATABASE nama_database

H Contoh: CREATE DATABASE COMPANY

n CREATE TABLE

H Untuk membentuk table dari basis data

H Untuk menyebutkan spesifikasi dan batasan atribut


DDL (2)DDL (2)

n Contoh CREATE TABLE:

CREATE TABLE EMPLOYEE

( PNAME CHAR(15) NOT NULL

LNAME CHAR(15) NOT NULL

SSN CHAR(9) NOT NULL

BDATE DATE

ADDRESS CHAR(30)

SEX CHAR

SALARYDECIMAL(10.2)

DNO CHAR(10) );


DDL (3)DDL (3)

n ALTER TABLE

HDigunakan untuk mengubah struktur table

HContoh kasus: misalkan ingin menambahkan kolom JOB pada table EMPLOYEE dengan tipe karakter selebar 12.

HPerintah:ALTER TABLE EMPLOYEE ADD JOB CHAR(12);


DDL (4)DDL (4)

n CREATE INDEX

HMembentuk berkas index dari table

H Index digunakan untuk mempercepat proses pencarian

HSintaks: CREATE [UNIQUE] INDEX nama_index ON nama_table(kolom1, kolom2, …. )

HContoh: CREATE INDEX EMPLOYEENDX ON EMPLOYEE(SSN)


DDL (5)DDL (5)

n Menghapus Basis Data

H DROP DATABASE

H Sintaks: DROP DATABASE nama_database

H Contoh: DROP DATABASE COMPANY

n Menghapus Table

H DROP TABLE

H Sintaks: DROP TABLE nama_table

H Contoh: DROP TABLE EMPLOYEE

n Menghapus Berkas Index

H DROP INDEX

H Sintaks: DROP INDEX nama_index

H Contoh: DROP INDEX EMPLOYEENDX


DML (1)DML (1)

n Bahasa untuk mengakses basis data

n Bahasa untuk mengolah basis data

n Bahasa untuk memanggil fungsi-fungsi agregasi

n Bahasa untuk melakukan query

n Jenis-jenis query:

H Sederhana

H Join

H Bertingkat


Schema Used in ExamplesSchema Used in Examples


Basic Structure Basic Structure

n SQL is based on set and relational operations with certain modifications and enhancements

n A typical SQL query has the form:select A1, A2, ..., An

from r1, r2, ..., rm

where P

H Ais represent attributes

H ris represent relations

H P is a predicate.

n This query is equivalent to the relational algebra expression.

∏A1, A2, ..., An(σP (r1 x r2 x ... x rm))

n The result of an SQL query is a relation.


Query Query SederhanaSederhana

n Bentuk umum SQL:

SELECT [ALL|DISTINCT]

nama_kolom_kolom_tabel

[INTO nama_tabel]

[FROM nama_nama_tabel]

[WHERE predikat]

[GROUP BY ekspresi]

[ORDER BY nama+kolom_tabel]


The select Clause (1)The select Clause (1)

n The select clause corresponds to the projection operation of the relational algebra. It is used to list the attributes desired in the result of a query.

n Find the names of all branches in the loan relationselect branch-namefrom loan

n In the “pure” relational algebra syntax, the query would be:

∏branch-name(loan)

n An asterisk in the select clause denotes “all attributes”

select *from loan

n NOTE: SQL does not permit the ‘-’ character in names, so you would use, for example, branch_name instead of branch-name in a real implementation. We use ‘-’ since it looks nicer!

n NOTE: SQL names are case insensitive, meaning you can use upper case or lower case.

H You may wish to use upper case in places where we use bold font.



n SQL allows duplicates in relations as well as in query results.

n To force the elimination of duplicates (menghilangkan duplikasi penampilan output yang sama) insert the keyword distinct after select.Find the names of all branches in the loan relations, and remove duplicates

select distinct branch-namefrom loan

n The keyword all specifies that duplicates not be removed.

select all branch-namefrom loan

n Menampilkan isi tabel customer

select * from customer

n Menampilkan semua fname dari tabel customer

select customer_name from customer



n Menampilkan account number dan balance dari kantor cabang (branch_name) “Pondok Kelapa”

select account_number, balancefrom account

where branch_name = “Pondok Kelapa”;

n Perintah diatas dapat juga dituliskan dengan menggunakan qualified column names sebagai berikut:

select account.account_number,

account.balancefrom account

where branch_name = “Pondok Kelapa”;



n The select clause can contain arithmetic expressions involving the operation, +, –, ∗, and /, and operating on constants or attributes of tuples.

n The query:

select loan-number, branch-name, amount ∗ 100from loan

would return a relation which is the same as the loan relations, except that the attribute amount is multiplied by 100.


The where Clause (1)The where Clause (1)

n The where clause corresponds to the selection predicate of the relational algebra. If consists of a predicate involving attributes of the relations that appear in the from clause.

n The find all loan number for loans made a the Perryridge branch with loan amounts greater than $1200.

select loan-numberfrom loanwhere branch-name = ‘Perryridge’ and amount > 1200

n Comparison results can be combined using the logical connectives and, or, and not.

n Comparisons can be applied to results of arithmetic expressions.


The where Clause (2)The where Clause (2)

n SQL Includes a between comparison operator in order to simplify where clauses that specify that a value be less than or equal to some value and greater than or equal to some other value.

n Find the loan number of those loans with loan amounts between $90,000 and $100,000 (that is, ≥$90,000 and ≤$100,000)

select loan-numberfrom loanwhere amount between 90000 and 100000


The from Clause The from Clause –– ContohContoh Query JoinQuery Join

n The from clause corresponds to the Cartesian product operation of the relational algebra. It lists the relations to be scanned in the evaluation of the expression.

n Find the Cartesian product borrower x loanselect ∗from borrower, loan

n Find the name, loan number and loan amount of all customers having a loan at the Perryridge branch.

select customer-name, borrower.loan-number, amountfrom borrower, loanwhere borrower.loan-number = loan.loan-number and

branch-name = ‘Perryridge’

n Contoh diatas merupakan Query Join dengan branch_name = “Perryridge” sebagai kondisi seleksi dan borrower.loan-number = loan.loan-number sebagai kondisi join


The Rename OperationThe Rename Operation

n The SQL allows renaming relations and attributes using the as clause:old-name as new-name

n Find the name, loan number and loan amount of all customers; rename the

column name loan-number as loan-id.

select customer-name, borrower.loan-number as loan-id, amount

from borrower, loan

where borrower.loan-number = loan.loan-number


String OperationsString Operations

n SQL includes a string-matching operator for comparisons on character strings.

n Find the names of all customers whose street includes the substring “Main”.

select customer-namefrom customerwhere customer-street like ‘%Main%’

n SQL supports a variety of string operations such as

H concatenation (using “||”)

H converting from upper to lower case (and vice versa)

H finding string length, extracting substrings, etc.


Ordering the Display of TuplesOrdering the Display of Tuples

n List in alphabetic order the names of all customers having a loan in Perryridge branch

select distinct customer-namefrom borrower, loanwhere borrower.loan-number = loan.loan-number and

branch-name = ‘Perryridge’order by customer-name

n We may specify desc for descending order or asc for ascending order, for each attribute; ascending order is the default.

H E.g. order by customer-name desc


Set Operations (1)Set Operations (1)

n The set operations union, intersect, and except operate on relations and correspond to the relational algebra operations ∪, ∩, −.

n Each of the above operations automatically eliminates duplicates; to retain all duplicates use the corresponding multiset versions union all, intersect all and except all.

Suppose a tuple occurs m times in r and n times in s, then, it occurs:

H m + n times in r union all s

H min(m,n) times in r intersect all s

H max(0, m – n) times in r except all s


Set Operations (2)Set Operations (2)

n Find all customers who have a loan, an account, or both:

(select customer-name from depositor)union(select customer-name from borrower)

n Find all customers who have both a loan and an account.

(select customer-name from depositor)intersect(select customer-name from borrower)

n Find all customers who have an account but no loan.

(select customer-name from depositor)except(select customer-name from borrower)


Aggregate Functions (1)Aggregate Functions (1)

n These functions operate on the multiset of values of a column of a relation, and return a value

avg: average valuemin: minimum valuemax: maximum valuesum: sum of valuescount: number of values


Aggregate Functions (2)Aggregate Functions (2)

n Find the average account balance at the Perryridge branch.

select avg (balance)from accountwhere branch-name = ‘Perryridge’

n Find the number of tuples in the customer relation.

select count (*)from customer

n Find the number of depositors in the bank.

select count (distinct customer-name)from depositor


Aggregate Functions Aggregate Functions –– Group ByGroup By

n Find the number of depositors for each branch.

select branch-name, count (distinct customer-name)from depositor, accountwhere depositor.account-number = account.account-numbergroup by branch-name

Note: Attributes in select clause outside of aggregate functions must appear in group by list


Aggregate Functions Aggregate Functions –– Having ClauseHaving Clause

n Find the names of all branches where the average account balance is more than $1,200.

select branch-name, avg (balance)from accountgroup by branch-namehaving avg (balance) > 1200

Note: predicates in the having clause are applied after the formation of groups whereas predicates in the where clause are applied before forming groups


Null Values (1)Null Values (1)

n It is possible for tuples to have a null value, denoted by null, for some of their attributes

n null signifies an unknown value or that a value does not exist.

n The predicate is null can be used to check for null values.

H E.g. Find all loan number which appear in the loan relation with null values for amount.

select loan-numberfrom loanwhere amount is null

n The result of any arithmetic expression involving null is null

H E.g. 5 + null returns null

n However, aggregate functions simply ignore nulls

H more on this shortly


Null Values and Three Valued Logic (2)Null Values and Three Valued Logic (2)

n Any comparison with null returns unknown

H E.g. 5 < null or null <> null or null = null

n Three-valued logic using the truth value unknown:

H OR: (unknown or true) = true, (unknown or false) = unknown(unknown or unknown) = unknown

H AND: (true and unknown) = unknown, (false and unknown) = false,(unknown and unknown) = unknown

H NOT: (not unknown) = unknown

H “P is unknown” evaluates to true if predicate P evaluates to unknown

n Result of where clause predicate is treated as false if it evaluates to unknown


Null Values and Aggregates (3)Null Values and Aggregates (3)

n Total all loan amounts

select sum (amount)from loan

H Above statement ignores null amounts

H result is null if there is no non-null amount, that is the

n All aggregate operations except count(*) ignore tuples with null values on the aggregated attributes.


Nested Nested Subqueries Subqueries –– Query Query BertingkatBertingkat

n SQL provides a mechanism for the nesting of subqueries.

n A subquery is a select-from-where expression that is nested within another query.

n A common use of subqueries is to perform tests for set membership, set comparisons, and set cardinality.

n Find all customers who have both an account and a loan at the bank.

select distinct customer-namefrom borrowerwhere customer-name in (select customer-name

from depositor)

n Find all customers who have a loan at the bank but do not have an account at the bank

select distinct customer-namefrom borrowerwhere customer-name not in (select customer-name

from depositor)


Example Nested QueryExample Nested Query

n Find all customers who have both an account and a loan at the Perryridge branch

select distinct customer-namefrom borrower, loanwhere borrower.loan-number = loan.loan-number and

branch-name = “Perryridge” and(branch-name, customer-name) in

(select branch-name, customer-namefrom depositor, accountwhere depositor.account-number =

account.account-number)

n Note: Above query can be written in a much simpler manner. The formulation above is simply to illustrate SQL features.

(Schema used in this example)


Set Comparison and Set Comparison and Tuple Tuple VariablesVariables

n Find all branches that have greater assets than some branch located in Brooklyn.

select distinct T.branch-namefrom branch as T, branch as Swhere T.assets > S.assets and

S.branch-city = ‘Brooklyn’

n Same query using > some clause

select branch-namefrom branchwhere assets > some

(select assetsfrom branch

where branch-city = ‘Brooklyn’)


Definition of Some Clause Existential QuantifierDefinition of Some Clause Existential Quantifier

n F <comp> some r ⇔ ∃ t ∈ r s.t. (F <comp> t)Where <comp> can be: <, ≤, >, =, ≠

056

(5< some ) = true

05

0

) = false

5

05(5 ≠ some ) = true (since 0 ≠ 5)

(read: 5 < some tuple in the relation)

(5< some

) = true(5 = some

(= some) ≡ inHowever, (≠ some) ≡ not in


Definition of all ClauseDefinition of all Clause

n F <comp> all r ⇔ ∀ t ∈ r (F <comp> t)

056

(5< all ) = false

610

4

) = true

5

46(5 ≠ all ) = true (since 5 ≠ 4 and 5 ≠ 6)

(5< all

) = false(5 = all

(≠ all) ≡ not inHowever, (= all) ≡ in


Example QueryExample Query

n Find the names of all branches that have greater assets than allbranches located in Brooklyn.

select branch-namefrom branchwhere assets > all

(select assetsfrom branchwhere branch-city = ‘Brooklyn’)


Test for Empty RelationsTest for Empty Relations

n The exists construct returns the value true if the argument subquery is nonempty.

n exists r ⇔ r ≠ Ø

n not exists r ⇔ r = Ø



n Find all customers who have an account at all branches located in Brooklyn.

select distinct S.customer-namefrom depositor as Swhere not exists (

(select branch-namefrom branchwhere branch-city = ‘Brooklyn’)

except(select R.branch-namefrom depositor as T, account as Rwhere T.account-number = R.account-number and

S.customer-name = T.customer-name))

n (Schema used in this example)

n Note that X – Y = Ø ⇔ X ⊆ Y

n Note: Cannot write this query using = all and its variants


Test for Absence of Duplicate TuplesTest for Absence of Duplicate Tuples

n The unique construct tests whether a subquery has any duplicate tuples in its result.

n Find all customers who have at most one account at the Perryridge branch.

select T.customer-namefrom depositor as Twhere unique (

select R.customer-namefrom account, depositor as Rwhere T.customer-name = R.customer-name and

R.account-number = account.account-number andaccount.branch-name = ‘Perryridge’)




n Find all customers who have at least two accounts at the Perryridge branch.

select distinct T.customer-namefrom depositor Twhere not unique (

select R.customer-namefrom account, depositor as Rwhere T.customer-name = R.customer-name and

R.account-number = account.account-number andaccount.branch-name = ‘Perryridge’)



ViewsViews

n Provide a mechanism to hide certain data from the view of certain users. To create a view we use the command:

create view v as <query expression>

where:

H <query expression> is any legal expression

H The view name is represented by v


Example QueriesExample Queries

n A view consisting of branches and their customerscreate view all-customer as

(select branch-name, customer-namefrom depositor, accountwhere depositor.account-number = account.account-number)

union(select branch-name, customer-namefrom borrower, loanwhere borrower.loan-number = loan.loan-number)

n Find all customers of the Perryridge branch

select customer-namefrom all-customerwhere branch-name = ‘Perryridge’


Derived RelationsDerived Relations

n Find the average account balance of those branches where the average account balance is greater than $1200.

select branch-name, avg-balancefrom (select branch-name, avg (balance)

from accountgroup by branch-name)as result (branch-name, avg-balance)

where avg-balance > 1200

Note that we do not need to use the having clause, since we compute the temporary (view) relation result in the from clause, and the attributes of result can be used directly in the where clause.


With ClauseWith Clause

n With clause allows views to be defined locally to a query, rather than globally. Analogous to procedures in a programming language.

n Find all accounts with the maximum balance

with max-balance(value) asselect max (balance)from account

select account-numberfrom account, max-balancewhere account.balance = max-balance.value


Complex Query using With Clause (PR)Complex Query using With Clause (PR)

n Find all branches where the total account deposit is greater than the average of the total account deposits at all branches

with branch-total (branch-name, value) asselect branch-name, sum (balance)from accountgroup by branch-name

with branch-total-avg(value) asselect avg (value)from branch-total

select branch-namefrom branch-total, branch-total-avgwhere branch-total.value >= branch-total-avg.value


Modification of the Database Modification of the Database –– DeletionDeletion

n Delete all account records at the Perryridge branch

delete from accountwhere branch-name = ‘Perryridge’

n Delete all accounts at every branch located in Needham city.

delete from accountwhere branch-name in (select branch-name

from branchwhere branch-city = ‘Needham’)

delete from depositorwhere account-number in

(select account-numberfrom branch, accountwhere branch-city = ‘Needham’

and branch.branch-name = account.branch-name)




n Delete the record of all accounts with balances below the average at the bank.

delete from accountwhere balance < (select avg (balance)

from account)

H Problem: as we delete tuples from deposit, the average balance changes

H Solution used in SQL:

1. First, compute avg balance and find all tuples to delete

2. Next, delete all tuples found above (without recomputing avg or retesting the tuples)


Modification of the Database Modification of the Database –– InsertionInsertion

n Add a new tuple to account

insert into accountvalues (‘A-9732’, ‘Perryridge’,1200)

or equivalently

insert into account (branch-name, balance, account-number)values (‘Perryridge’, 1200, ‘A-9732’)

n Add a new tuple to account with balance set to null

insert into accountvalues (‘A-777’,‘Perryridge’, null)


Modification of the Database Modification of the Database –– InsertionInsertion

n Provide as a gift for all loan customers of the Perryridge branch, a $200 savings account. Let the loan number serve as the account number for the new savings account

insert into accountselect loan-number, branch-name, 200from loanwhere branch-name = ‘Perryridge’

insert into depositorselect customer-name, loan-numberfrom loan, borrowerwhere branch-name = ‘Perryridge’

and loan.account-number = borrower.account-number

n The select from where statement is fully evaluated before any of its results are inserted into the relation (otherwise queries like

insert into table1 select * from table1would cause problems


Modification of the Database Modification of the Database –– UpdatesUpdates

n Increase all accounts with balances over $10,000 by 6%, all other accounts receive 5%.

H Write two update statements:

update accountset balance = balance ∗ 1.06where balance > 10000

update accountset balance = balance ∗ 1.05where balance ≤ 10000

H The order is important

H Can be done better using the case statement (next slide)


Case Statement for Conditional UpdatesCase Statement for Conditional Updates

n Same query as before: Increase all accounts with balances over $10,000 by 6%, all other accounts receive 5%.

update accountset balance = case

when balance <= 10000 then balance *1.05else balance * 1.06

end


Update of a ViewUpdate of a View

n Create a view of all loan data in loan relation, hiding the amount attribute

create view branch-loan asselect branch-name, loan-numberfrom loan

n Add a new tuple to branch-loan

insert into branch-loanvalues (‘Perryridge’, ‘L-307’)

This insertion must be represented by the insertion of the tuple

(‘L-307’, ‘Perryridge’, null)

into the loan relation

n Updates on more complex views are difficult or impossible to translate, and hence are disallowed.

n Most SQL implementations allow updates only on simple views (without aggregates) defined on a single relation


Transactions (1)Transactions (1)

n A transaction is a sequence of queries and update statements executed as a single unit

H Transactions are started implicitly and terminated by one of

4 commit work: makes all updates of the transaction permanent in the database

4 rollback work: undoes all updates performed by the transaction.

n Motivating example

H Transfer of money from one account to another involves two steps:

4 deduct from one account and credit to another

H If one steps succeeds and the other fails, database is in an inconsistent state

H Therefore, either both steps should succeed or neither should

n If any step of a transaction fails, all work done by the transaction can be undone by rollback work.

n Rollback of incomplete transactions is done automatically, in case of system failures


Transactions (2)Transactions (2)

n In most database systems, each SQL statement that executes successfully is automatically committed.

H Each transaction would then consist of only a single statement

H Automatic commit can usually be turned off, allowing multi-statement transactions, but how to do so depends on the database system

H Another option in SQL:1999: enclose statements withinbegin atomic

… end


Joined Relations (PR)Joined Relations (PR)

n Join operations take two relations and return as a result another relation.

n These additional operations are typically used as subquery expressions in the from clause

n Join condition – defines which tuples in the two relations match, and what attributes are present in the result of the join.

n Join type – defines how tuples in each relation that do not match any tuple in the other relation (based on the join condition) are treated.

Join Types

inner joinleft outer joinright outer joinfull outer join

Join Conditions

naturalon <predicate>using (A1, A2, ..., An)


Joined Relations Joined Relations –– Datasets for ExamplesDatasets for Examples

n Relation loan

amount

3000

4000

1700

n Relation borrower

customer-name loan-number

Jones

Smith

Hayes

L-170

L-230

L-155

branch-name

Downtown

Redwood

Perryridge

loan-number

L-170

L-230

L-260

n Note: borrower information missing for L-260 and loan information missing for L-155


Joined Relations Joined Relations –– Examples Examples

n loan inner join borrower onloan.loan-number = borrower.loan-number

branch-name amount

Downtown

Redwood

3000

4000


Jones

Smith

L-170

L-230

branch-name amount

Downtown

Redwood

Perryridge

3000

4000

1700


Jones

Smith

null

L-170

L-230

null

loan left inner join borrower onloan.loan-number = borrower.loan-number

loan-number

L-170

L-230

loan-number

L-170

L-230

L-260


Joined Relations Joined Relations –– ExamplesExamples

n loan natural inner join borrower

branch-name amount

Downtown

Redwood

3000

4000

customer-name

Jones

Smith

loan natural right outer join borrower

branch-name amount

Downtown

Redwood

null

3000

4000

null

customer-name

Jones

Smith

Hayes

loan-number

L-170

L-230

loan-number

L-170

L-230

L-155


Joined Relations Joined Relations –– ExamplesExamples

n loan full outer join borrower using (loan-number)

branch-name amount

Downtown

Redwood

Perryridge

null

3000

4000

1700

null

customer-name

Jones

Smith

null

Hayes

Find all customers who have either an account or a loan (but not

both) at the bank.select customer-namefrom (depositor natural full outer join borrower)where account-number is null or loan-number is null

loan-number

L-170

L-230

L-260

L-155

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