SQL data definition using Oracle1 SQL Data Definition using Oracle.

SQL data definition using Oracle 1

SQL Data Definition

using Oracle


DDL

• SQL = DDL + DML– Oracle has its own dialect of SQL

• DDL (Data definition language)– Part of SQL

• Some DDL statements– create table …– alter table …– drop table …


Naming conventions

• Naming conventions for table names and attributes names– Illegal

• spaces• hyphens

– Legal• letters [a-z A-Z, not æøå] + digits• _, #, $• first character must be a letter• no reserved words in SQL [no attribute called 'by‘ or ‘table’]


Data types

• Slightly different from standard SQL• Strings• Numbers• Dates• Other

– no Boolean data type

• Documentation– http://docs.oracle.com/cd/B28359_01/

server.111/b28318/datatype.htm


Data types, strings

• varchar2 (max_length)– varying length, like names, etc.– Varchar2(10)

• Max length 10 bytes

– Varchar2(10 char)• Max length 10 chars• Normally 1 char ~ 1 byte, but it depends on the character

table (like UNICODE)

• char (fixed_length)– fixed length, like cpr, phone, etc– Length in bytes or chars, like varchar2


Data types, numbers

• Numbers– number (digits, decimals)

• fixed number of digits and decimals, like price, salary, etc.

– number (digits) integer– number floating point (high precision)


Data types, dates

• date– store date and time!

• no special time data type

– Oracle SQL has special functions to do arithmetic on dates

• more on that when we look at "select …"

– advice• don't make an attribute called "age", as it changes

frequently.• make an attribute called birthday.


Data types, other

• CLOB character large object– texts up to 4 gigabytes

• BLOB binary large object– up to 4 gigabytes, pictures, sounds, etc.

• NCLOB– like CLOB, but using 2 bytes pr. character

• BFILE binary file– reference to a binary file outside the DBMS


Constraints, types

• Types of constraints– integrity constraints

• primary key• foreign key

– value constraints• not null• unique


Constraints, naming

• A constraints must have a name to be able to– alter the constraints– delete the constraint

• naming convention– tableName_attributeName_constraintType– student_cpr_pk

• If you don’t name your constraints Oracle will name them. Find the names– select * from user_constraints where table_name =

'PERSON';


Constraints, defining + primary key

• 2 ways to define a constraint– column level, applied to one attribute

create table student ( cpr char (9) constraint student_cpr_pk primary key, …)

– table level, can be applied to more attributescreate table student_course ( cpr char(9) not null, course_number number(3) not null, constraint student_cpr_pk primary key (cpr, course_number))


Constraints, not null• The attribute must no be NULL.

– syntaxes• name varchar2(30) not null no name constraint• name varchar2(30) constraint student_name_nn not null• can not be specified at table level [only at attribute level]

– primary key attributes must be NOT NULL– NULL means

• does not exist• is not known at the moment

– Don't make your own NULL's using 0 or ‘ ‘– Don’t write NOT NULL to often.

• Think before you write!


Constraints, unique

• The value of an attribute must be unique– used when a table has more candidate keys

• one of the candidates is appointed primary key• the rest of the candidates are [only] unique

– syntaxes• attribute level

– departmentName varchar(12) unique

• table level– constraint student_name_uk unique (firstname,

lastname) unlikely constraint!!


Constraints, foreign key• Attributes in one table refers to attributes in

[another] table.– DBMS checks if the referred attributes exist.

• referential integrity

– Examplecreate table student_course (

cpr char(9) not null,

course_number number(3) not null constraint student_course_number_fk references course (course_number),

constraint student_cpr_pk primary key (cpr, course_number),

constraint student_cpr_fk foreign key (cpr) references student (cpr)

);


Referential triggered actions• foreign key … on delete cascade

– if the referred row is deleted the referring row should be deleted as well

create table employee (cpr char(9) primary key,…boss_cpr char(9),foreign key (boss_cpr) references employee (cpr) on delete

cascade))• If we delete the top boss the whole organization vanishes!!

– think carefully before writing … on delete cascade• useful in weak entity sets

– no … on update cascade in Oracle!!• not necessary if we use surrogate keys (they never change)


Constraint, check

• Checking business rules

• General constraint that every row must satisfy– attribute level

• salary number(5) check ( salary >= 0 )• gender char(1) check (gender in ('M', 'F'))

– table level• check (gender ='M' or salary < '1000')


Default value + domains

• No a constraint, but has similar syntax.• Used when no value is supplied

– country char(2) default 'DK'– salary number(5) default 0

• Oracle has no domain concept– No create domain …– But there is a create type …


Creating a table

• Tables are usually created by a DBA (Database administrator)

• Tables are usually not created from an application.– SQLite (used in Android + iOS) is an

exception


Displaying table information

• Forgot the name of your tables?– Select table_name from user_tables– User_tables has information in all your tables

• Forgot the name + type of attributes?– Describe Person


Alter table

• Changing an existing table– add / delete attributes– add / delete constraints– most alternations are restricted [hard to do] so

design your tables carefully before creating them!!

– syntax• alter table tableName theAlternation• alter table student add mobilPhone char(8)


Chicken and egg problem, creation

• From http://www-db.stanford.edu/~ullman/fcdb/oracle/or-triggers.html

• Problem– If table A refers to table B and vice versa

which table should be created first?

• Solution– create table A without foreign key to B– create table B with foreign key to A– alter table A adding a foreign key to B

http://www-db.stanford.edu/~ullman/fcdb/oracle/or-triggers.html


Chicken and egg, examplecreate table chicken ( cID number(3) primary key, eID number(3))-------------------------create table egg ( eID number (3) primary key, cID number (3),foreign key (cID) refers to chicken (cID) initially deferred deferrable)------------------------alter table chicken add constraint chicken_eID_fk foreign key (eID) refers to egg (eID) initially deferred deferrable


Chicken and egg, insertion

• How to insert rows into the tables?• Problem

– an egg row refers to a chicken row, and vice versa

• Solution (Oracle)– create the foreign keys with "initially deferred

deferrable"• defers constraint checking until transaction commit• insert into chicken (1,2)• insert into egg (2,1)• commit


Drop tables

• truncate table tableName– remove all data from the table, but the [not empty]

table still exists.– use carefully!!

• drop table– deletes the table including data– use carefully!!– Referential integrity

• You are not allowed to drop a table if another table refer to it

• rename oldTableName to newTableName

SQL data definition using Oracle1 SQL Data Definition using Oracle.

Documents

SQL data definition using Oracle1 SQL Data Definition using Oracle.