SQL data definition using Oracle1 SQL Data Definition using Oracle

SQL data definition using Oracle2 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 Oracle3 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 Oracle4 Data types Slightly different from standard SQL Strings Numbers Dates Other –no Boolean data type Documentation – b28318/datatype.htm

SQL data definition using Oracle5 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 Oracle6 Data types, numbers Numbers –number (digits, decimals) fixed number of digits and decimals, like price, salary, etc. –number (digits)integer –numberfloating point (high precision)

SQL data definition using Oracle7 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.

SQL data definition using Oracle8 Data types, other CLOBcharacter large object –texts up to 4 gigabytes BLOBbinary large object –up to 4 gigabytes, pictures, sounds, etc. NCLOB –like CLOB, but using 2 bytes pr. character BFILEbinary file –reference to a binary file outside the DBMS

SQL data definition using Oracle9 Constraints, types Types of constraints –integrity constraints primary key foreign key –value constraints not null unique

SQL data definition using Oracle10 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 Oracle11 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 Oracle12 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!

SQL data definition using Oracle13 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 Oracle14 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 Oracle15 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 Oracle16 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 Oracle17 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 …

SQL data definition using Oracle18 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

SQL data definition using Oracle19 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

SQL data definition using Oracle20 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)

SQL data definition using Oracle21 Chicken and egg problem, creation 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 Oracle22 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 Oracle23 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 Oracle24 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