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2. Complete SQL

Tianqing Zhang

School of Computer

(School of Software)

SCU 2006

Tianqing Zhang SCU 2

2.1 Basic SQL

• SQL (Structured Query Language) – The de facto standard query language for relational D

BMSs 事实标准– both DDL (Data Definition Language) and DML (Data

Manipulation Language)– A historical note

• SQL1 (ANSI 1989)• SQL2 or SQL-92 (ANSI 1992)• SQL3 (SQL99)

– 学习方法：背命令，实践，理解


2.1.1 SQL Data Definition Language

• Creating a Database – Understanding SQL Data Types – Numeric Data – Character Strings – Bit Strings

• Temporal Data • Date and Time • Intervals • Operations on Dates

• Creating a Domain • Creating a Table • Destroying a Table • Modifying a Table Schema


Backus Naur Form notation

• upper-case reserved words• lower-case user-defined words• | choice• { } a required element • [ ] an optional element• [ ，… ] optional repetitions


Creating a Schema 1

• Why?– 允许多个用户使用一个数据库而不会干扰其它用户。 – 把数据库对象组织成逻辑组，让它们更便于管理。 – 第三方的应用可以放在不同的模式中，这样它们就不

会和其它对象的名字冲突。


Creating a Schema 2

• How?– CREATE SCHEMA database-name [AUTHORIZA

TION user-identifier]; – 访问在模式中的对象 : schema.table

• Public Schema: [public.]table– DROP SCHEMA database-name [RESTRICT | CASCA

DE]; • RESTRICT 受限有对象，不能删• CASCADE 级联有对象，一起删


SQL Data Types 1

• Boolean Data– BOOLEAN TURE/FALSE

• Numeric Data– Exact Numbers

• INTEGER (INT ， INT4) 2,147,483,648 to 2,147,483,647 • SMALLINT -32768 to 32767• BIGINT (INT8) 8 位整数

– Approximate Numbers• FLOAT[precision]• REAL• DOUBLE PRECISION

– Formatted Numbers• DECIMAL(i,j), DEC(i,j) or NUMERIC(i,j)


SQL Data Types 2

• Character Strings– Fixed length n

• CHAR(n) or CHARACTER(n) 定长串不足充空 space

– Varying length of maximum n• VARCHAR(n) or CHAR VARYING (n) 变长串 • VARCHAR2(n) ORACLE 用

• Bit Strings– Fixed length n: BIT(n) 定长位串– Varying length of maximum n: VARBIT(n) or BIT VARYIN

G (n) 变长位串


SQL Data Types 3

• Temporal Data 日期时间– Date and Time

• DATE stores calendar values representing YEAR, MONTH, and DAY.

– ‘2000-02-29’ 推荐 to_date('2000/02/29' , ‘yyyy/mm/dd' )

• TIME defines HOURS, MINUTES, and SECONDS in a twenty-four-hour notation: HH:MM:SS

• TIME(i) defines i additional decimal fractions of seconds: HH:MM:SS:ddd...d.

– Example, in TIME(4), a time could be 22:20:01:2345

• TIME WITH TIME ZONE includes the displacement [+13:00 to -12:59] from standard universal time zone: HH:MM:SS+/-hh:mm.

• TIMESTAMP represents a complete date and time with six fractions of seconds and optional time zone. 时间戳 postgreSQL now( ) 函数


SQL Data Types 4

• Intervals 间隔 – An interval results when two dates are subtracted.

• Example: OrderDate – ShipDate• INTERVAL YEAR (3) to MONTH could be an interval between 0-0

(0 years and 0 months) and 999-11 (999 years and 11 months). SQL 标准

• postgreSQL 形式 ‘ 999 YEAR 11 MONTH’• INTERVAL DAY(2) to MINUTE could be an interval between 00:00:

00 (0 days. 0 hours, 0 minutes) to 99:23:59 (99 days, 23 hours, and 59 minutes).

• postgreSQL ‘99 day 23 hour 59 minute’

– A date plus or minus an interval yields a new date.• CURRENT_DATE + INTERVAL '1' MONTH• postgreSQL CURRENT_DATA +’ 1 MONTH’


SQL Data Types 5

• Valid combinations of DATETIME and intervals : – Datetime - Datetime = Interval of year/month or day/ti

me – Datetime (+ or -) Interval = Datetime – Interval (* or /) Number = Interval – Interval (+ or -) Interval = Interval


An Example


Creating a Domain

• Domain 域– SQL-92 allows the definition of new data types, more precisely d

ata type macros, for columns expressed in terms of the basic data types but not in terms of other domains. 用基本类型定义

– Syntax• CREATE DOMAIN domainName [AS] dataType

[DEFAULT defaultOption] [CHECK (searchCondition)]

– Example• CREATE DOMAIN hour_dom AS INTEGER DEFAULT 0 CHECK (VALUE >=

0); • CREATE DOMAIN genderDom AS CHAR

DEFAULT ‘M’CHECK (VALUE IN (‘F’, ‘f’,‘M’ ,‘m’)); -- 定义

• gender genderDom NOT NULL -- 使用


Creating a Table 1

• SyntaxCREATE TABLE tableName ({columName dataType [NOT NULL] [UNIQUE] [DEFAULT defaultOption] [CHECK (searchCondition)] [,…] } [PRIMARY KEY (listOfColumns),] {[UNIQUE (listOfColumns),] [,…]} {[FOREIGN KEY (listOfFireignKeyColumns) REFERENCES parentTableName [ (listOfCandidateKeyColumn

s)], [MATCH {PARTIAL | FULL} [ON UPDATE referentialAction] [ON DELETE referentialAction]] [,…]} {[CHECK (searchCondition)] [,…] } )


Creating a Table 2

• An Example:CREATE TABLE BOOK ( Book_Id NUMERIC(6) NOT NULL,

Edition NUMERIC(3) NOT NULL, BorrowerMemNo NUMERIC(4), BorrowDueDate DATE, CallNumber VARCHAR(8) NOT NULL, LibCheck ssn_dom,PRIMARY KEY (Book_Id), FOREIGN KEY (BorrowerMemNo) REFERENCES MEMBER(MemNo), FOREIGN KEY (CallNumber) REFERENCES TITLE(CallNumber), FOREIGN KEY (LibCheck) REFERENCES LIBRARIAN(SSN)

);


Creating a Table 3

• Primary and foreign keys can be specified at the same level as the definition of the column, as long as they are simple atomic ones. 如果单值，主外码也可定义为列级完整性约束

CREATE TABLE LIBRARIAN ( SSN ssn_dom NOT NULL PRIMARY KEY,

Name name_dom NOT NULL,Address address_dom,Salary DEC(4.2) DEFAULT 0.0 CHECK(Salary >= 0),Gender gender_dom, Birthday DATE, SUPERSSN ssn_dom FOREIGN KEY REFERENCES LIBRARIAN(SSN), Section sectno_dom FOREIGN KEY REFERENCES SECTION(SectionId)

);


Creating a Table 4

• Primary keys composed of more than one column can be specified.

CREATE TABLE DEPENDENT( LIBSSN ssn_dom,

Name name_dom NOT NULL, Birthday DATE, Kinship CHAR(5) DEFAULT 'none', PRIMARY KEY (LIBSSN, Name), FOREIGN KEY (LIBSSN) REFERENCES LIBRARIAN(SSN)

);


Creating a Table 5

• The unique key word specifies each row must have unique values -- specify that a set of columns may serve as an alternate key. 备选码

CREATE TABLE BOOK ( Book_Id NUMERIC(6) NOT NULL,

Edition NUMERIC(3) NOT NULL, BorrowerMemNo NUMERIC(4), BorrowDueDate DATE, CallNumber VARCHAR(8) NOT NULL UNQUE, LibCheck ssn_dom,Primary Key (Book_Id), FOREIGN KEY (BorrowerMemNo) REFERENCES MEMBER(MemNo), FOREIGN KEY (CallNumber) REFERENCES TITLE(CallNumber), FOREIGN KEY (LibCheck) REFERENCES LIBRARIAN(SSN)

);


Destroying a Table

• SyntaxDROP TABLE tableName [ RESTRICT | CASCADE ]

– With the CASCADE option, the table and all references to it are removed.

– With the RESTRICT option, the table is removed if it is not referenced. 默认

• Example– DROP TABLE MEMBER CASCADE;– DROP TABLE MEMBER RESTRICT;


Modifying a Table Schema 1

• Syntax

ALTER TABLE tableName [ADD [COLUMN] columnName dataType [NOT NULL] [UNIQUE][DEFAULT defaultOption] [CHECK (searchCondition)]][DROP [COLUMN] columnName [ RESTRICT | CASCADE ]][ADD [CONSTRAINT [constraintName]]tableConstraintDefinition][DROP CONSTRAINT constraintName [ RESTRICT | CASCADE ]][ALTER [COLUMN] SET DEFAULT defaultOption][ALTER [COLUMN] DROP DEFAULT]



• ALTER TABLE table-name ALTER – 修改字段数据类型

• ALTER TABLE LIBRARIAN ALTER Salary NUMBER(6,2);

• ALTER TABLE LIBRARIAN ALTER COLUMN Salary TYPE NUMBER(6,2); --p

ostgreSQL– 改变字段的缺省值

• ALTER TABLE DEPENDENT ALTER COLUMN kinship DROP DEFAULT;

• ALTER TABLE BOOK ALTER COLUMN BorrowerMemNo SET DEFAULT NULL;

– 增加一个不能写成表约束的非空约束• ALTER TABLE products ALTER COLUMN product_no SET NOT NUL

L;



• ALTER TABLE table-name ADD – 增加字段

• ALTER TABLE products ADD COLUMN description text ; – 增加约束

• ALTER TABLE products ADD CHECK (name <> ''); • ALTER TABLE products

ADD CONSTRAINT some_name UNIQUE (product_no);

• ALTER TABLE products ADD FOREIGN KEY (product_group_id) REFERENCES product_groups;



• ALTER TABLE table-name DROP– 删除字段

• ALTER TABLE products DROP COLUMN description RESTRICT; -- 默认受限删除

• ALTER TABLE products DROP COLUMN description CASCADE; --CASCADE 授权删除任何依赖该字段的东西

– 删除约束 • ALTER TABLE products DROP CONSTRAINT constraint_na

me; • ALTER TABLE products ALTER COLUMN product_no DROP

NOT NULL;


2.1.2 SQL Data Manipulation Language

• The Complete SELECT Statement– Syntax

SELECT [DISTINCT | ALL] { * | [columnExpression [AS newName]] [,…] }FROM tableName [alias] [,…][WHERE condition] -- 元组条件[GROUP BY columnList] -- 分组

[HAVING condition] -- 分组条件[ORDER BY columnList] -- 排序

– Example 全表查询

SELECT * FROM BOOK;


SELECT Statement 1

• Resulting Tables as Sets– If duplicate elimination is desired, it can be achieved u

sing the DISTINCT keyword in the SELECT clause. 消重

SELECT DISTINCT CallNumber FROM BOOK;


SELECT Statement 2

• Aliasing in SQL: The AS Operator 别名– Renaming attributes in the result of a query: 结果属性

别名SELECT Name AS Librarian_Name

FROM LIBRARIANWHERE Salary > 18000;

– Table alias can be achieved with the AS operator in the FROM-clause 表别名

SELECT * FROM LIBRARIAN AS L WHERE L.name = 'Ruchi Jones';


SELECT Statement 3

• Calculated fields– Example:Produce a list of monthly salaries for all libra

rians, showing the name and the monthly salary details.

SELECT staffNo,fName,lName,salary/12FROM Staff;

SELECT staffNo,fName,lName,salary/12 AS monthlySalary

FROM Staff;


SELECT Statement 4

• Comparing NULL Values– NULL can appear in a column 不能用 = <> 来比较– SQL provides the IS NULL and IS NOT NULL operato

rs to test for NULL values 用 IS NULL 和 IS NOT NULL 来比较

SELECT Book_id FROM BOOK WHERE BorrowerMemNo IS NULL;


SELECT Statement 5

• NULL 引起的三值逻辑问题– 三值

• True• False• Unknown

– WHERE 子句为真的才被选出• 引入 IS NOT FALSE• Example: 区别？SELECT Name

FROM LibarianWHERE Salary < 29000 AND Gender = 'M‘;

SELECT Name FROM LibarianWHERE (Salary < 29000 AND Gender = 'M') IS NOT FALSE;


SELECT Statement 6

• Range Conditions– Range search conditions, like the condition "retrieve all

the librarians whose salary is between 25000 and 35000“, will be expressed with a conjunction

SELECT * FROM LIBRARIAN WHERE Salary >= 25000 AND Salary <= 35000;

– Using the BETWEEN operator

SELECT * FROM LIBRARIAN WHERE Salary BETWEEN 25000 AND 35000;


SELECT Statement 7

• Pattern Matching and String Concatenation– A percent sign `%‘ indicates a match with an arbitrary

number of characters including spaces. % 任意个字符– An underscore sign ‘_’ matches a single arbitrary char

acter. _ 一个字符– Example 1: Retrieve all the Librarians whose first nam

e is Nick.

SELECT SSN, Name

FROM LIBRARIAN

WHERE Name LIKE 'Nick%';


SELECT Statement 8

• Pattern Matching and String Concatenation– A percent sign `%‘ indicates a match with an arbitrary

number of characters including spaces. % 任意个字符– An underscore sign ‘_’ matches a single arbitrary char

acter. _ 一个字符– Example 2: Display in a single column the full name of

all members in Pittsburgh (area code number 412) who have phone numbers, the first digit of which is a 6 and the third a 3. || 连接串

SELECT Fname || MI || Lname AS Name, PhoneNumber FROM MEMBER WHERE PhoneNumber LIKE '(412) 6_3%';


SELECT Statement 9

• Pattern Matching and String Concatenation– In the event that the search pattern includes a percent

sign, we can use an escape character to cause the SQL interpreter to interpret the percent sign as itself. 如何表示 & 和 _ 本身？转义字

– Example: Display the name and call number of all the book titles that contain '10%' as part of the title name.

SELECT Name, CallNumber FROM TITLES WHERE Name LIKE '%10&%%' ESCAPE '&';


SELECT Statement 10

• Set membership search condition (IN/NOT IN)– Example: List all managers and supervisors.

SELECT staffNo,fName,lName,positionFROM StaffWHERE position IN (‘Manager’, ‘Supervisor’);

– Example: List all librarians who are not managers and supervisors.

SELECT staffNo,fName,lName,positionFROM StaffWHERE position NOT IN (‘Manager’, ‘Supervisor’);

SELECT staffNo,fName,lName,positionFROM StaffWHERE position NOT IN (‘Manager’, ‘Supervisor’) is not fal

se;


SELECT Statement 11

• Aggregate Functions– Five aggregate functions:SUM, MAX, MIN, AVG, and COUNT

五个基本集函数– Example: Display all the statistics about librarian salaries.

SELECT SUM (Salary) AS TotalSalaries, -- 求和MAX (Salary) AS MaxSalary, --最大值MIN (Salary) AS MinSalary, --最小值AVG (Salary) AS AvgSalary, --平均值COUNT (*) AS Cardinality, -- 元组计数COUNT (DISTINCT Salary) AS Salarylevels –不重复非空值计数

FROM LIBRARIAN;


SELECT Statement 12

• Aggregate Functions– Distinguish between count(*) and count(column). cou

nt(*) 对所有选出元组计数， count(column)只对 column 非 NULL 的原组计数。

– Example:

SELECT count(*)

FROM librarian;

SELECT count(salary)

FROM librarian;


SELECT Statement 13

• Grouping in SQL: The GROUP BY and HAVING Clauses 分组分组限制– In SQL, we can group rows together based on the val

ue of some attributes that we call the grouping attributes.

– Example: List the call number of the books that have more than two editions.

SELECT CallNumber, COUNT(*) AS NoPopularBooks FROM BOOK WHERE Edition >= 3 GROUP BY CallNumber;


SELECT Statement 14

• Grouping in SQL: The GROUP BY and HAVING Clauses 分组分组限制– The HAVING clause to select only those groups that we are inter

ested in. HAVING短语对分组进行限制– Example: assume that we are interested in finding out the numb

er of copies of the popular books (for example, with Edition >=3), for which at least five copies exist in the library.

SELECT CallNumber, COUNT(*) AS NoPopularBooks FROM BOOK WHERE Edition >= 3 -- 元组限制GROUP BY CallNumber -- 分组HAVING COUNT (*) >= 5; -- 分组限制


SELECT Statement 15

• Grouping in SQL: The GROUP BY and HAVING Clauses 分组分组限制– A wrong example:SELECT Book_Id, CallNumber, COUNT(*) AS NoPopul

arBooks FROM BOOK WHERE Edition >= 3 GROUP BY CallNumber;

– It’s wrong, why?


SELECT Statement 16

• Grouping in SQL: The GROUP BY and HAVING Clauses 分组分组限制– A wrong example:SELECT Book_Id, CallNumber, COUNT(*) AS NoPopul

arBooks FROM BOOK WHERE Edition >= 3 GROUP BY CallNumber;

– It’s wrong, why?– SELECT后一般只能出现集函数和 GROUP BY后的分

组列


Nested Queries and Set Comparisons

• In some queries, the selection conditions can be expressed more easily in terms of set comparisons. 查询中使用集合– Explicit definition ： (1, 2, 3) ， ('Science', 'Art', 'Children'). – Implicit definition ： use an inner SELECT statement (subquery) w

hose output table (set) is used by the selection condition of the outer SELECT statement in order to produce the final result. nested queries 嵌套查询

• SELECT MemNo, Fname, MI, Lname FROM MEMBER WHERE MemNo = - -必须保证子

查询单值( SELECT BorrowerMemNo

FROM BOOK WHERE Book_id = 999);


Set Membership 1

• The IN and NOT IN operators check for simple membership.– Example ： List each head librarian's SSN, along with

their section, except those of the Science, Art, and Children sections.

– SELECT HeadSSN, Name FROM SECTION WHERE Name NOT IN ('Science', 'Art', 'Children');


Set Membership 2

• The IN and NOT IN operators check for simple membership.– Example ： List each head librarian's SSN, along with

their section, except those of the Science, Art, and Children sections.

– SELECT HeadSSN, Name FROM SECTION WHERE Name NOT IN ('Science', 'Art', 'Children');

– 思考：如果 Name 为 NULL ，情况怎样？


Set Membership 3

• IS NOT FALSE:– SELECT HeadSSN, Name

FROM SECTION WHERE Name NOT IN ('Science', 'Art', 'Children')

IS NOT FALSE; - - 允许 NULL• IS TRUE:

– SELECT HeadSSN, Name FROM SECTION WHERE Name NOT IN ('Science', 'Art', 'Children')

IS TRUE; - - 明确不允许 NULL ，可省略


Set Membership 4

• An example using the IN operator ：– List the last names of all librarians who are not head l

ibrarians.– SELECT LName

FROM LIBRARIAN WHERE SSN NOT IN

(SELECT LIBSSN FROM SECTION) IS NOT FALSE;


Quantified Set Comparisons 1

• The test for membership, which is an equality comparison, can be generalized to other comparisons ( =, <>, >, >=, <, <= ) and can be quantified using ANY (that is, SOME) or ALL.– Comparisons ( =, <>, >, >=, <, <= ) 要求子查询单值，类型可比，

子查询只能在比较运算符右边。• Example ： List the SSN of all librarians whose salary is lower than t

hat of the librarian whose SSN is ‘S3-07-021’.• SELECT SSN

FROM LibrarianWHERE salary <

(SELECT salary FROM Librarian WHERE SSN = ‘S3-07-021’);



– Comparisons ( =, <>, >, >=, <, <= ) + (ANY or ALL) 实现各种复杂语义

• > ANY 不是最小， >= ALL 最大，…• Example 1 ： List the SSN of all librarians whose salary is th

e lowest in the library.• SELECT SSN

FROM Librarian

WHERE salary <= ALL

(SELECT salary

FROM Librarian);



– Comparisons ( =, <>, >, >=, <, <= ) + (ANY or ALL) 实现各种复杂语义

• Example 2 ： List the name and SSN of all head librarians whose salary is lower than that of any librarian who is not a head librarian.

• SELECT Name, SSN FROM LIBRARIAN, SECTION WHERE SSN = HeadSSN AND salary < AN

Y (SELECT Salary FROM LIBRARIAN L WHERE L.SSN NOT IN ( SELECT HeadSSN FROM SECTI

ON ) IS NOT FALSE);


Set Comparisons: EMPTY and UNIQUE 1

• The EXISTS (not empty) and NOT EXISTS (empty) operators test for emptiness of a result. 存在测试– Example 1: List the names and SSNs of all librarians who are no

t head librarians.– SELECT L.SSN, L.Name

FROM LIBRARIAN L

WHERE NOT EXISTS

(SELECT *

FROM SECTION

WHERE L.SSN = HeadSSN); - -内外层相关– 相关子查询：计算时，类似两重循环。外层带值入内层，测试是否有值。



• The EXISTS (not empty) and NOT EXISTS (empty) operators test for emptiness of a result.– Example 2: List the member numbers of all library me

mber who haven’t borrowed any book.– SELECT MemNo

FROM Member M

WHERE NOT EXISTS

(SELECT *

FROM Book

WHERE M.MemNo = BorrowerMemNo); - -内外层相关



• NOT EXISTS 可实现除操作– Example 3: List the member numbers of all library mem

ber who likes all books written by ‘Thomas’.– SELECT MemNo

FROM Member MWHERE NOT EXISTS (SELECT * FROM Book B WHERE Author = ‘Thomas’ AND NOT EXISTS(SELECT * FROM LIKE L WHERE M.MemNo = L.MemNoAND L.CallNumber=B. CallNumber));



• The UNIQUE and NOT UNIQUE operators test for duplicates in a result. 唯一测试– Example: List the names and SSNs of all librarians wit

h more than one dependent.– SELECT Name,SSN

FROM Library L

WHERE NOT UNIQUE

(SELECT * FROM DEPENDENT WHERE LIBSSN = L.SSN);


Joining Tables in SQL2 1

• Wher Join 传统方式– Example 1 ： List the last names of the library members and his

borrowed book Id.SELECT Lname, Book_Id

FROM Member,BookWHER MemNo=BorrowerMemNo; -- 连接条件

– Example 2 ： List the last names of the library members who likes books written by ‘Thomas’.

SELCT LnameFROM Member,Like,Book -- 三表连接WHERE Member.MemNo=Like.MemNo AND Like.Callnumber=Book.Callnumber

AND Book.Author=‘Thomas’;



• SQL2 introduced JOIN in order to separate the selection and join conditions, leaving the WHERE clause for selection only.– Example 1 ： List the last names of the library members and his

borrowed book Id.SELECT Lname, Book_Id

FROM Member JOIN Book ON MemNo = BorrowerMemNo;– Example 2 ： List the last names of the library members who like

s books written by ‘Thomas’.SELCT Lname

FROM (Member M JOIN Like L ON M.MenNo= L.MenNo) JOIN Book B ON L.Callnumber=B. Callnumber

WHERE Book.Author=‘Thomas’;



– Example 3 ： list only once the last name and address of all the members with a borrowed book and whose first name is Andreas or Rebecca.

– SELECT DISTINCT Lname, Address

FROM (MEMBER JOIN BOOK ON MemNo = BorrowerMemNo)

WHERE Fname = 'Andreas' or Fname = 'Rebecca';



• Four types of join: NATURAL JOIN (自然连接 ) and outer joins (LEFT OUTER JOIN 左外连接 , RIGHT OUTER JOIN 右外连接 , and FULL OUTER JOIN 全外连接 ). – NATURAL JOIN

• SELECT * FROM Member NATURAL JOIN Book WHERE Fname LIKE ‘%be’;

– LEFT OUTER JION （左外连接相当于左表扩展右表属性）• SELECT *

FROM Member LEFT OUTER JOIN Book ON MemNo=BorrowerMemNO WHERE Fname LIKE ‘%be’;

• 即使 Member 表（左表）的某元组匹配不到 Book 表（右表）的元组，该元组也将出现在结果中，对应的 Book 表的属性为 NULL 。



– RIGHT OUTER JION 右外连接右表扩展• SELECT *

FROM Member RIGHT OUTER JOIN Book ON MemNo=BorrowerMemNO WHERE Fname LIKE ‘%be’;

• 即使 Book 表（右表）的某元组匹配不到Member 表（左表）的元组，该元组也将出现在结果中，对应的 Book 表的属性为 NULL 。

– FULL OUTER JION 全外连接双向扩展• SELECT *

FROM Member FULL OUTER JOIN Book ON MemNo=BorrowerMemNO WHERE Fname LIKE ‘%be’;

• 即使 Member 表（左表）的某元组匹配不到 Book 表（右表）的元组，该元组也将出现在结果中，对应的 Book 表的属性为 NULL；同时，即使 Book 表（右表）的某元组匹配不到Member 表（左表）的元组，该元组也将出现在结果中，对应的 Book 表的属性为 NULL 。



• AS phrase is supported in FROM clause.– SELECT Name

FROM (LIBRARIAN NATURAL JOIN SECTION) AS S

WHERE S.Name = 'Children';


More on the Insert Command 1

• The implicit form. INSERT with implicit specification of attributes 不指定属性– INSERT INTO BOOK VALUES (999, 2, NULL, NULL, 'Q

A7.56B7', NULL); • The explicit form. INSERT with implicit specificati

on of attributes 指定属性– INSERT INTO BOOK (Book_id, Edition, CallNumber)

VALUES (999, 2, 'QA7.56B7'); – INSERT INTO BOOK (Edition, CallNumber, Book_id)

VALUES (2, 'QA7.56B7', 999);


More on the Insert Command 2

• The tuples to be inserted into a table would be derived from the database using the SELECT statement 插入查询结果– CREATE TABLE Section_Info

(SectCode section_dom primary key,

NumLibrarian INT

);– INSERT INTO Section_Info (SectCode, NumLibrarian)

SELECT SectNo, Count(*)

FROM LIBRARIAN, SECTION

WHERE Section = SectNo

GROUP BY SectNo;


Modifying data in the database (UPDATE) 1

• Syntax– UPDATE TableName

SET columnName1=value [, columnName1=value…]

[WHERE searchCondition]• Examples

– Example 1: Give all librarians 5% pay increase.– UPDATE librarian

SET salary = salary*1.05;



• Examples– Example 2: Give all librarians works in ‘Art’ section (say sectio

n 3) 5% pay increase. – UPDATE librarian

SET salary = salary*1.05WHERE section = 3;

– UPDATE librarianSET salary = salary*1.05WHERE section =

(SELECT sectno FROM sction WHERE name = ‘Art’);



• Examples– Example 3: Change Ashoka Savasere’s section From

‘History’ to ‘Art’ Section and give him 5% pay increase. – UPDATE librarian

SET section=(SELECT Sectno FROM Section

WHERE Name='Art'),

salary=salary*1.05

WHERE name='Ashoka Savasere‘ AND section =

(SELECT SectNo

FROM Section

WHERE name=‘History’);


Deleting data from the database (DELETE)

• Syntax– DELETE FROM TableName

[WHERE searchCondition]

• Examples– Example 1: Delete all librarians. (Delete all rows.)– DELETE FROM librarian;– Example 2: Delete all librarians works in ‘checkout’ section. (Del

ete specific rows.) – DELETE FROM librarian

WHERE section =

(SELECT sectno FROM section

WHERE name = ‘checkout’);


更新与参照完整性约束 1

• 当对两个有引用关系的表数据更新时，可能引起完整性约束被破坏– Example 1: 更新外码值

create table t1

( a int primary key,

b int

);

create table t2

( c char(10) primary key,

d int references t1

);



insert into t1(a,b) values(1,1);

insert into t1(a,b) values(2,2);

insert into t2(c,d) values('aa',1);

insert into t2(c,d) values('bb',2);

update t2 set d=3 where c='bb';

ERROR: insert or update on table "t2" violates foreign key constraint "t2_d_fkey"

DETAIL: Key (d)=(3) is not present in table "t1".



– Example 2 ：删除被引用的码值delete from t1 where a=1;ERROR: update or delete on "t1" violates foreign key constraint "t2

_d_fkey" on "t2"DETAIL: Key (a)=(1) is still referenced from table "t2".– 增加删除外码约束的 action ： set null 置空值

alter table t2 drop constraint t2_d_fkey;alter table t2 add constraint t2_d_fkey foreign key (d) references t1 on

delete set null;postgres=# delete from t1 where a=1;DELETE 1postgres=# select * from t2; bb | 2 aa |



– 增加删除外码约束的 action ： cascade 级联alter table t2 drop constraint t2_d_fkey;

alter table t2 add constraint t2_d_fkey foreign key (d) references t1 on delete cascade;

postgres=# delete from t1 where a=1;

DELETE 1

postgres=# select * from t2;

bb | 2



– Example 3 ：修改被引用的码值postgres=# update t1 set a=3 where a=1;ERROR: update or delete on "t1" violates foreign key constraint "t2

_d_fkey" on "t2"DETAIL: Key (a)=(1) is still referenced from table "t2".– 增加修改外码约束的 action ： set null 置空值

alter table t2 drop constraint t2_d_fkey;alter table t2 add constraint t2_d_fkey foreign key (d) references t1 on

delete set null on update set null;postgres=# update t1 set a=3 where a=1;UPDATE 1postgres=# select * from t2; bb | 2 aa |



– 增加修改外码约束的 action ： cascade 级联alter table t2 drop constraint t2_d_fkey;

alter table t2 add constraint t2_d_fkey foreign key (d) references t1 on delete cascade on update cascade;

postgres=# update t1 set a=3 where a=1;

UPDATE 1

postgres=# select * from t2;

bb | 2

aa | 3