Using SQL to create tables Ways of using Databases

Revisiting database structure External Schema Conceptual Schema Internal Schema Physical Schema

SQL Standard Query Language is used widely to access databases. Implemented SQL (Oracle, MS SQL Server, Access) varies a little from the standard, but is reasonably standard It consists of a data definition language - DDL (Create, Alter, Drop) And a Data Manipulation Language - DML (Select, Union, Update, Delete, Insert Into, Select Into, Transform, Parameter)

DLL - Add a table CREATE TABLE table_name {(column_name data_type [NOT NULL] [UNIQUE][DEFAULT default_option] [CHECK (search_condition)][,…]} [PRIMARY KEY (list_of_columns),] {[UNIQUE (list_of_columns),][,…]} {[FOREIGN KEY {(list_of_foreign_key_columns) REFERENCES parent_table_name[(list_of_candidate_key_columns)], [MATCH {PARTIAL | FULL} {[CHECK (search_condition)][,…]}) [] optional, {} one or more, lower case – user supplied names, upper case reserved words, [|] either or, () are part of the syntax.

Basic create DDL - Create a table Create table Publisher (PubID VARCHAR(10) NOT NULL, PubName VARCHAR(100), PubPhone VARCHAR(20)) Create table Books (ISBN VARCHAR(13) NOT NULL, Title VARCHAR(100), Price Decimal(7,2), PubID VARCHAR(10))

With keys Create table Publisher (PubID VARCHAR(10) UNIQUE NOT NULL, PubName VARCHAR(100), PubPhone VARCHAR(20), primary key (PubID)) Create table Books (ISBN VARCHAR(13), Title VARCHAR(100), Price Decimal(7,2), PubID VARCHAR(10), PRIMARY KEY (ISBN), FOREIGN KEY (PubID) REFERENCES PUBLISHER)

DDL - Add a table Syntax is as follows:- CREATE TABLE TableName (ColumnDefinition,… [,Multi-ColumnConstraint,…]); Column definition is ColumnDefinition ::= ColumnName DataType[(size)][Single-ColumnConstraint]

DDL - Single column constraint Single-ColumnConstraint:== CONSTRAINT IndexName [PRIMARY KEY | UNIQUE | REFERENCES ReferencedTable [(ReferencedColumn,…)] ] The ReferencedColumn is only necessary if the field being referenced is not the primary key of the referenced table

DDL - Multi-column constraints This constraint clause appears after all column definitions: CONSTRAINT IndexName [PRIMARY KEY (ColumnName,…) | UNIQUE (ColumnName,…) | FOREIGN KEY (ReferencingColumn,…) REFERENCES ReferencedTable[(ReferencedColumn,…)] ]

DDL - Create a table Create table Publisher (PubID TEXT(10) CONSTRAINT PrimaryKeyName PRIMARY KEY, PubName TEXT(100), PubPhone TEXT(20)); Create table Books (ISBN TEXT(13) CONSTRAINT PrimaryKeyName PRIMARY KEY, Title TEXT(100), Price MONEY, PubID TEXT(10) CONSTRAINT FOREIGN KEY PubID REFERENCES PUBLISHER(PubID));

DDL - ALTER or DROP TABLE Alter is used to –Add a new column to the table –Delete a column from the table Drop is used to delete a table

DDL - Syntax for Alter and Drop ALTER TABLE TableName ADD ColName ColType[(size)] [unique][not null] | DROP COLUMN ColName DROP TABLE TableName

Populating and Querying tables Insert, Update, Delete and View (DML)

Inserting data into a table To add a row of data to a table INSERT INTO VALUES (value1, value2, …valueN) If the value list matches the column list exactly, there is no need to list the column names. If the value list does not match the column list exactly, there is a need to list the column names.

Example insert into Expert values ( ,'Dr. O''Meara','Orthopaedic'); Where the expert table was set up as:- CREATE TABLE Expert ( Expert_Id numeric(7,0), Expert_Name varchar(50), Expertise_area varchar(15), PRIMARY KEY (Expert_Id)) Note also, if you want to put an apostrophe in a string, put in two apostrophes.

Delete Delete from expert where expert_id = ; This deletes all rows from the expert table that have an expert_id of Please note that you can only delete a row if no other row depends on it.

Referential integrity The above tables have no foreign keys and a straightforward insert does not compromise referential integrity. If a table is constrained by foreign key values, then there is a need to see what is in the other table. Retrieving data from a database –Data can be retrieved from a table or set of tables using the SELECT statement

Exercise The following tables form part of a database held in a relational DBMS: –Hotel (Hotel_No, Name, Address) –Room (Room_No, Hotel_No, Type, Price) –Booking (Hotel_No,Guest_No, Date_from, Date_To, Room_No) –Guest (Guest_No, Name, Address) where –Hotel contains hotel details and Hotel_No is the primary key, –Room contains room details for each hotel and (Hotel_No, Room_No) forms the primary key, –Booking contains details of the bookings and the primary key comprises (Hotel_No, Guest_No and Date_From) –Guest contains guest details and Guest_No is the primary key. Create the database.