From theory to practice. Designing Tables for an Oracle Database System. Sqlplus. Sqlplus. Technicalities. Add the following to your.

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1 From theory to practice Designing Tables for an Oracle Database System The Entity-Relationship model: a convenient way of representing the world. The Relational model: a model for organizing data using tables. Oracle: a database infrastructure which implements the relational model. Converting ER->Relational model is important! SQL(Structured Query Language): A language used to get information from an oracle database. 1 2 Sqlplus Oracle is a commercial, hardware-based, heavy(!), program. To connect to it, we use the Sqlplus utility. The Sqlplus program accepts commands in standard SQL and sends them to the Oracle database. The interface creates a local database for each user. Technicalities Add the following to your.cshrc file: if (-r ~db/oraenv) source ~db/oraenv You will be able to use Oracle after you log out and log in again. 3 4 Connecting to the Oracle Database At the command line prompt, write: Sqlplus (not sqlplus!) This will give you access to the personal database of user (In other words, to access your database, you have to run it from your own CS account). You will be presented with a Sqlplus console, in which you type your commands. To disconnect (and return to your regular shell), type: quit Remember: (almost) Every command must end with a semicolon (;) 5 6 1

2 CPU Reminder The database is kept on the disk, so anything you create will be there next time you log on. Main Memory sailors Reserves DISK Running Commands from an.sql File Instead of typing commands into the SQLPLUS terminal, you can load commands from a file (no special format is required). The file should end with.sql Invoke by: 1. Use the from SQLPLUS to load the file file.sql Or: 2. Invoke the SQLPLUS command with the extra to load the file at connection: 7 8 Spooling the Output Output can be placed in a file: spool <file_> Spooling can be turned off with: spool off Tables The basic element in Oracle is a table. A table has columns (attributes), and rows (tuples). Every column has a Name and Type (of the data it stores), and some columns have constraints. Some tables may have additional constraints Id Creating Tables in SQL Name Eyal Yair Ori Dept. Sales Transport Warehouse Age Creating a Table The basic format of the CREATE TABLE command is: CREATE TABLE TableName( Column1 DataType1 ColConstraint, ColumnN DataTypeN ColConstraint, TableConstraint1, TableConstraintM

3 Example NUMBER NOT NULL, F VARCHAR2(20), L VARCHAR2(20), Gender CHAR(1), Dept NUMBER 13 An Example (cont.) Oracle is case insensitive in Column s! If you type describe Employee you get: Name Null? Type FNAME LNAME GENDER NOT NULL NUMBER VARCHAR2(20) VARCHAR2(20) CHAR(1) SALARY NOT NULL NUMBER(5) DEPT NUMBER Notice that describe describes the structure and not the contents of the table. 14 CHAR(n) VARCHAR2(n) CLOB BLOB DATE TIMESTAMP NUMBER NUMBER(n) NUMBER(n,m) Others Examples of Data Types String of fixed length n (n <= 2000) Variable length string of size <= n (n <= 4000) Character large object (<= 4GB) Binary large object (<= 4GB) Val dates (up to seconds) Val timestamps (up to milliseconds) Up to 40 digits Integer of size n Number of size n with m digits after decimal place XML, Abstract types, etc. 15 What happens if we insert: 'abc' into char(5)? 'abc' into varchar(5)? 'abc' into char(2)? 'abc' into varchar(2)? into number(3,2)? into number(5,2)? into number(4,1)? into number(3)? into number? into number(7,5)? abc abc Wrong! Wrong! Wrong! Wrong! Why not always use number and not number(n,m)? Why not always use varchar2(4000)? Where is the boolean datatype? 16 Constraints in Create Table Adding constraints to a table enables the database system to enforce data integrity. However, adding constraints also makes inserting data slower. Different types of constraints: * Not Null * Default Values * Unique * Primary Key * Foreign Key * Check Condition Not Null Constraint SSN NUMBER NOT NULL, F VARCHAR2(20), L VARCHAR2(20), Gender CHAR(1), Dept NUMBER

4 Default Values Unique Constraint (Syntax 1) SSN NUMBER NOT NULL, F VARCHAR2(20), L VARCHAR2(20), Dept NUMBER SSN NUMBER UNIQUE NOT NULL, F VARCHAR2(20), L VARCHAR2(20), Dept NUMBER Unique Constraint (Syntax 2) Unique Constraint (Another Example) SSN NUMBER NOT NULL, F VARCHAR2(20), L VARCHAR2(20), Dept NUMBER, UNIQUE(SSN) 21 SSN NUMBER NOT NULL, F VARCHAR2(20), L VARCHAR2(20), Dept NUMBER, UNIQUE(F, L) Can this be written differently? 22 Primary Key Constraint Primary Key Constraint (Syntax 2) SSN NUMBER PRIMARY KEY, F VARCHAR2(20), L VARCHAR2(20), Dept NUMBER, UNIQUE(F, L) Primary Key implies: * NOT NULL * UNIQUE. There can only be one primary key. SSN NUMBER, F VARCHAR2(20), L VARCHAR2(20), DeptNumber NUMBER, UNIQUE(F, L), PRIMARY KEY(ssn)

5 Another Table CREATE TABLE Department( DeptNumber NUMBER PRIMARY KEY, Name VARCHAR2(20), ManagerId NUMBER Shouldn t all department numbers in Employee appear in Department? 25 Foreign Key Constraint NUMBER PRIMARY KEY, F VARCHAR2(20), L VARCHAR2(20), DeptNumber NUMBER, UNIQUE(F, L), FOREIGN KEY (DeptNumber) REFERENCES Department(DeptNumber) DeptNumber must be unique (or primary key) in Department 26 Foreign Key Constraint (Syntax 2) NUMBER PRIMARY KEY, F VARCHAR2(20), L VARCHAR2(20), DeptNumber NUMBER, UNIQUE(F, L), FOREIGN KEY (DeptNumber) REFERENCES Department NOTE: You can use this syntax only if the of the fields in both tables are entical 27 Employee FName Larry Magic Foreign Key LName Bird Johnson Department Gender M M Dept Sallary Dept Name Sales Repair Foreign Key Man Understanding Foreign Keys Deleting a Referenced Value The constraint on the last table should be read as: The field Dept in Employee is a foreign key that references the field Dept in Department Meaning: Every non-null value in the field Dept of Employee must appear in the field Dept of Department. What happens to Employees in department 312 when Department 312 is removed from the Department table? If nothing additional is specified, then Oracle will not allow Department 312 to be deleted if there are Employees working in (referencing to) this department. If the constraint is written as FOREIGN KEY (Dept) REFERENCES Department ON DELETE CASCADE then Employees working in 312 will be deleted automatically from the Employee table, when 312 is deleted from Departments

6 Foreign Keys Foreign Key We should revise the Department table: FName LName Gender Sallary DeptNum CREATE TABLE Department( DeptNumber NUMBER PRIMARY KEY, Name VARCHAR2(20), ManagerId NUMBER, FOREIGN KEY (ManagerId) REFERENCES Employee(SSN) DeptNum Name Man Foreign Key Do you see a problem in defining these tables and in inserting data now? Solution to Cyclic Constraints Add one of the constraints later on (after insertion): CREATE TABLE Department( Dept NUMBER PRIMARY KEY, Name VARCHAR2(20), ManagerId NUMBER Insert data here ALTER TABLE Department ADD(FOREIGN KEY (ManagerId) REFERENCES Employee(SSN) Check Conditions A check condition is a Boolean expression: And s and Or s of conditions of the type X > 5 On a column: it can refer only to the column On a table: it can refer only to multiple columns in the table Check Constraints SSN NUMBER PRIMARY KEY, F VARCHAR2(20), L VARCHAR2(20), Gender CHAR(1) DEFAULT( F ) CHECK(Gender = F or Gender = M ), CHECK (Gender = M or Salary > 10000) Deleting a Table To delete the table Employee : DROP TABLE Employee; Mind the order of dropping when there are foreign key constraints. Why? Can use: DROP TABLE Employee cascade constraints;

7 General Principals Converting ER-Diagrams to Table Definitions When converting ER diagrams to Relations, we should try to: Note: 1. Reduce duplicate information 2. Constrain as tightly as possible 1. Some scenarios can be represented in different ways. 2. Sometimes we will not be able to fully represent constraints, or will be forced to represent information more than once Relations vs. Tables We show how to translate ER-Diagrams to table definitions Sometimes, people translate ER-Diagrams to relation definition, which is more abstract than table definitions. e.g., Employee(SSN, F, L, Gender, Salary, Dept table definitions contain, in addition, constraints and datatypes 39 General Rule: Simple entity translation Create a table with the of the Entity. There is a column for each attribute birthday The key in the diagram is the primary key of the table 40 Student Simple entity translation birthday student Relation: (,, birthday, ) 41 create table ( varchar2(20) primary key, varchar2(40), birthday date, varchar2(100) 42 7

8 Translating Entities with Relationships birthday (without constraints) title birthday (without constraints) title Acted In Film Acted In Film Create tables for the entities as before Create a table with the of the relationship Relationship table attributes: its own attributes () + all keys of the relating entities (title, ). Q: What is the primary key of the table? A: A composite of both entity keys Q: What foreign keys are needed? A: From the relationship table to the entities type 43 type How would you define the table for ActedIn? 44 How would we represent this diagram in Answer tables? תאריך נבחן מס' מס' קורס זהות מס' בחינה סטודנט מס' שם זהות בחינה מס' בחינה קורס שם מס' קורס קורס מס ' קורס שם ק ורס קורס תאריך נבחן שם סטודנט מס' זהות בחינה מס' בחינה Translating Recursive Relationships (without constraints) manager (key constraints): Option 1 Employee worker Manages Relation: Manages (W, M) What would be the table definition? create table Manages( E varchar2(20), M varchar2(20), Foreign key E references Employee(), Foreign key M references Employee(), Primary key(e, M) If we want to make sure an employee is not his own manager we can express it with Check 47 Option 1: Same as without key constraints (3 tables), except that the relationship primary key is? title. 48 8

9 (key constraints): Option 1 (key constraints): Option 2 create table Directed( varchar2(20), title varchar2(40), integer, primary key (title), foreign key references, foreign key title references Film Option 2: Do not create a table for the relationship Add information columns that would have been in the relationship's table to the table of the entity with the key constraint (key constraints): Option 2 (participation constraints) create table Film( title varchar2(40), integer, primary key (title), varchar2(20), integer, foreign key() references Why couldn t we do this when there were no constraints? 51 General Rule: If both participation and key constraint exist, use Option 2 from before (only 2 tables), and: Add the not null constraint on the referncing attribute to ensure that there will always be values for the key of the other entity 52 (participation constraints) (participation constraints) Acted In Film title create table Film( title varchar2(40), integer, varchar2(20), integer, foreign key () references, primary key (title) Where should we add NOT NULL? 53 How would we translate this? 54 9

10 Translating Weak Entity Sets Organization Gives Award phone number money A regular table for Organization, and.. create table award( ) varchar2(40), integer, money number(6,2), o_ varchar2(40), primary key(,, o_), foreign key (o_) references Organization() on delete cascade 55 Translating ISA: Option 1 Movie Person ISA picture create table MoviePerson(... ) create table ( varchar2(20), picture bfile, primary key(), foreign key () references MoviePerson)) create table (...) 56 Translating ISA: Option 2 Which Option To Choose? Movie Person ISA We use option 2 only if the lower-level entity sets ( and ): picture No table for MoviePerson! Cover the high-level entity set Are disjoint create table ( varchar2(20), varchar2(100), varchar2(20), picture blob, primary key() create table (...) O Organization Gives phone number picture Translating Aggregation Acted In Simple Entity Tables Single table Summary Primary key The entity key Remarks a column for each attr. Award Won Broadcasted title Film type Simple Relationship Key constraint 3 (2 entities +relationship) 3 as before or For the relation: Both entity keys Key of constrained ent. Foreign keys from rel. Table Foreign keys from rel. Table Won(title,,, O, Broadcasted 2 (one for each entity) Foreign key from constr. Entity 59 Key and Participation constr. 2 Regular Constrained entity has a non-null f. key 60 10

11 Tables Primary key Remarks Weak Entity 2: parent and weak entities Weak: its own and parent keys Foreign keys from weak ent. ISA: covers and disjoint 2: only child entities Parent key ISA: otherwise 3: parent and child entities Parent key Foreign keys from child ent. Aggregation 3: 2 aggregates and relationship For relationship: keys of both aggregates Foreign keys from relationship table 61 11