1. SQL data definition using Oracle

2. 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 …
SQL data definition using Oracle

3. SQL data definition using Oracle
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’]
SQL data definition using Oracle

4. SQL data definition using Oracle
Data types
Slightly different from standard SQL
Strings
Numbers
Dates
Other
no Boolean data type
SQL data definition using Oracle

5. SQL data definition using Oracle
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
SQL data definition using Oracle

6. SQL data definition using Oracle
Data types, numbers
Numbers
number (digits, decimals)
fixed number of digits and decimals, like price, salary, etc. (with number(4,2) - the max number is )
number (digits) integer
number floating point (high precision)
SQL data definition using Oracle

7. SQL data definition using Oracle
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 later.
advice
don't make an attribute called "age", as it changes frequently.
make an attribute called birthday.
SQL data definition using Oracle

8. SQL data definition using Oracle
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
SQL data definition using Oracle

9. SQL data definition using Oracle
Constraints, types
Types of constraints
integrity constraints
primary key
foreign key
value constraints
not null
unique
SQL data definition using Oracle

10. SQL data definition using Oracle
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';
SQL data definition using Oracle

11. 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 attributes
create table student_course (
cpr char(9) not null,
course_number number(3) not null,
constraint student_cpr_pk primary key (cpr, course_number)
SQL data definition using Oracle

12. Constraints, foreign key
Attributes in one table refers to attributes in [another] table.
DBMS checks if the referred attributes exist.
referential integrity
Example
create 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) );
SQL data definition using Oracle

13. 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)
SQL data definition using Oracle

14. SQL data definition using Oracle
Constraints, not null
The attribute must not 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!
SQL data definition using Oracle

15. SQL data definition using Oracle
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!!
SQL data definition using Oracle

16. SQL data definition using Oracle
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')
SQL data definition using Oracle

17. Default value + domains
Not 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 …
SQL data definition using Oracle

18. SQL data definition using Oracle
Creating a table
General syntax in Oracle CREATE TABLE [schema.] tablename (column1 datatype [CONSTRAINT constraint_name] constraint_type…, column2 datatype [CONSTRAINT constraint_name] constraint_type, [CONSTRAINT constraint_name] constraint_type (column, …), …);
SQL data definition using Oracle

19. Creating a table (CONT’D)
Examples
CREATE TABLE location
(RoomId NUMBER(2),
Building VARCHAR2(7) CONSTRAINT location_building_nn NOT NULL,
RoomNo CHAR(3) CONSTRAINT location_roomno_nn NOT NULL,
Capacity NUMBER(2) CONSTRAINT location_capacity_ck CHECK (Capacity>0),
RoomType CHAR;
CONSTRAINT location_roomid_pk PRIMARY KEY(RoomId),
CONSTRAINT location_roomno_uk UNIQUE(RoomNo));
SQL data definition using Oracle

20. 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 COURSE
SQL data definition using Oracle

21. SQL data definition using Oracle
Alter table
Altering 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)
SQL data definition using Oracle

22. Chicken and egg problem
From
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
SQL data definition using Oracle

23. Chicken and egg, example
create 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
SQL data definition using Oracle

24. 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
SQL data definition using Oracle

25. SQL data definition using Oracle
Drop tables, etc
truncate table tableName
remove all data from the table, but the table still exists.
use carefully!!
drop table
deletes the table including data
Referential integrity
You are not allowed to drop a table if another table refer to it solution: ALTER TABLE egg DROP CONSTRAINT chicken_eID_fk
rename oldTableName to newTableName
SQL data definition using Oracle