ZEIT2301 Design of Information Systems SQL: Creating a Database School of Engineering and Information Technology Dr Kathryn Merrick

Topic 10: SQL Basics This lecture will introduce the SQL for Creating a database Inserting data Updating data Making simple queries We will then compare how this is done in MS Access When can SQL be used? When is it hidden?

Structured Query Language SQL, the “Structured Query Language”, has become the standard language for data manipulation in relational databases SQL is a non-procedural language - it specifies what is to be done, not how it is to be done Relatively easy to use for simple queries some subtleties in more complex queries

4 Statements in SQL’s Data Manipulation Language INSERT – add data to a table UPDATE – modify data in a table DELETE – remove data from a table SELECT – retrieve data from database most commonly used statement (next lecture)

Remember our bike example in 3NF Bike name* Number of riders* Centre of mass height Harley Harley Honda Honda Road conditions* Coefficient of friction Icy0.1 Wet0.5 Dry0.9 Scenario ID* Bike name Number of riders Road conditions Can stoppie 1Harley1Dryfalse 2Harley2Dryfalse 3Honda1Drytrue 4Honda2Drytrue Bike name*Wheelbase Harley1.588 Honda1.458

Creating Relations: Example 1 CREATE TABLE Bikes (bikeName VARCHAR(60) NOT NULL UNIQUE, wheelbase DECIMAL(4, 3) NOT NULL, PRIMARY KEY (bikeName));

Common SQL Data Types Data TypeDescription INTEGERUp to 11 digits; –ve sign takes one place. SMALLINTUp to 6 digits, including sign. NUMERIC(s,d)Fractional numbers, with a maximum of s digits and d decimal places; d can be omitted. DECIMAL(s,d)Fractional numbers, with a minimum of s digits and d decimal places; d and s can be omitted. CHAR(s)Character strings, with s places provided. VARCHAR(s)Unpadded character strings, up to length s. DATETen character date representation (year month day) as digits. BOOLEANBoolean

Creating Relations: Example 2 CREATE TABLE CoMHeight(bikeName VARCHAR(60) NOT NULL UNIQUE, numRiders INTEGER NOT NULL comHeight DECIMAL(4, 3) NOT NULL, CONSTRAINT pk2 PRIMARY KEY (bikeName) CONSTRAINT fk1 FOREIGN KEY (bikeName) REFERENCES Bikes ON UPDATE CASCADE ON DELETE NO ACTION);

SQL Constraints Constraint TypeDescription CONSTRAINT… PRIMARY KEY… Supports entity integrity. Defines the primary key column(s). Must be NOT NULL and UNIQUE CONSTRAINT…FOREIGN KEY… ON UPDATE … ON DELETE… Supports referential integrity Regulates update/delete operations that have implications to other relations Foreign Key Subclause Values CASCADEUpdate/delete rows from parent table and automatically update/delete matching rows in child tables SET NULLUpdate/delete rows from parent table and set the foreign key values in child table to NULL NO ACTIONReject the update/delete operation

Inserting Records into a Relation INSERT INTO Bikes VALUES (‘Harley’, 1.588); INSERT INTO Bikes VALUES (‘Honda’, 1.458); INSERT INTO Bikes VALUES(‘Mongoose Expert’, 0.932); INSERT INTO CoMHeight VALUES(‘Harley’, 0, 0.724);

Inserting Records From a File It may not be practical to write insert statements for every record To read multiple records from a file in bulk: LOAD DATA LOCAL INFILE filename INTO TABLE Bikes FIELDS TERMINATED BY ‘\t’;

Viewing Records: Simple SELECT SELECT * FROM Bikes; SELECT scenarioID, canStoppie FROM Scenarios; SELECT * FROM CoMHeight WHERE bikeName = ‘Harley’; SELECT * FROM CoMHeight WHERE numRiders > 1;

Modifying Records UPDATE Bikes SET wheelbase = 1.6 WHERE bikeName = ‘Harley’ UPDATE CoMHeight SET comHeight = WHERE bikeName = ‘Harley’ AND numRiders = 1;

Deleting Records DELETE FROM CoMHeight WHERE bikeName = ‘Honda’; DELETE FROM CoMHeight WHERE numRiders = 2;

MS Access

Summary After today’s lecture you should be able to: Create and update a relational database using SQL