Computer Science 101 Web Access to Databases SQL – Basic Queries

SQL Introduction Structured Query Language Originally called SEQUEL from Structured English QUEry Language SQL has a standard SQL provides both –Data Definition Language (DDL) – Data Manipulation Language (DML) DBMS may provide higher level approach, but SQL is important for tougher queries, using host programming or web programming.

SQL - Basic Queries Basic form of SQL query: SELECT FROM [WHERE ] would be a list of columns separated by commas, etc. [ ] enclose optional clauses SQL is not case sensitive

SQL - Basic Queries -Conceptually SELECT FROM [WHERE ] Step 1: Make “long” rows by combining rows from the various tables in FROM clause in every possible way – each row in first table with each row in second table with each row in third table, etc. Step 2: Keep the long rows that satisfy WHERE condition. Step 3: Keep only columns specified in SELECT.

SQL - Basic Queries Example: Pose a query to get the names of all students: SELECT LastName, FirstName FROM Students

SQL - Basic Queries (cont.) Names of freshmen students

SQL - Basic Queries (cont.) Names of students from Fredericksburg

SQL - Basic Queries (cont.) Names of students from Fredericksburg

SQL - Basic Queries (cont.) Names of students from Fredericksburg

SQL - Basic Queries (cont.) Dump the Students table: SELECT * FROM Students Get names of departments having majors in our database –SELECT Department FROM Majors –SELECT DISTINCT Department FROM Majors

SQL - Basic Queries –Joining tables based on foreign key Connecting students with their advisors: we need to have AdvisorID = FacultyID Students(StudentID,FirstName, LastName, ClassYear, City, State, Zip, BirthDate, AdvisorID, Term) Faculty (FacultyID, FirstName, LastName, Phone, )

SQL - Basic Queries –Joining tables based on foreign key Connecting majors with their department chairs: we need to have ChairID = FacultyID Majors(MajorID, MajorName, Department, ChairID) Faculty (FacultyID, FirstName, LastName, Phone, )

SQL - Basic Queries – Joining tables Student last name, advisor last name OR (aliasing)

SQL - Basic Queries – Joining tables

SQL - Basic Queries –Joining tables based on intermediate table Connecting students with their interests: we need to have Students.StudentID = StudentInterest.StudentID AND StudentInterest.InterestID = Interests.InterestID Students(StudentID,FirstName, LastName, ClassYear, City, State, Zip, BirthDate, AdvisorID, Term) StudentInterest(StudentID, InterestID) Interests(InterestID, InterestName, Category, URL)

SQL - Basic Queries –Joining tables based on intermediate table Connecting students with majors: we need to have Students.StudentID = StudentMajor.StudentID AND StudentMajor.MajorID = Majors.MajorID Students(StudentID,FirstName, LastName, ClassYear, City, State, Zip, BirthDate, AdvisorID, Term) StudentMajor(StudentID, MajorID) Majors(MajorID, MajorName, Department, ChairID)

SQL - Basic Queries – Joining tables (cont.) Student last name, first name, name of NFL team student is interested in.

SQL - Basic Queries – Joining tables (cont.)