[igCS] Database Query

[igCS] Database Query

Objectives

• Learn about what is database query and why we need it

• Types of querying method

Open Ended

Recalled from what we previously learnt, what are the two fundamental function of a database?

Database query

• Filtering results from data in the Db with the given criteria

• (imagine it as a question to ask the computer about data)

Activity: Query for our class

• All students that wear glasses

• All students from F4B

• All students where they are NOT from F4B

• All students who's glasses=Yes AND from F4B

• All students where class=F4B AND class=F4C

How is the query looks like in computer?

• One most common language for database is called SQL (Structural Query Language)

• SQL is supported by most major database system

• MS Access also supports using GUI in query building, we call it QBE (Query By Example)

How SQL looks like:

• SELECT * FROM Students WHERE class="F4B"

• translates to: Select all students which class is F4B

• 
  

How QBE looks like

• We will create in Access...

Create a few more query

• All students who's glasses=Yes AND from F4B

• All students who's LastName starts with 'C'

• All students who is wearing glasses OR who is from F4A

Further

• All students, who's class is F4A, order by their LastName, displays ONLY their firstName and glasses

• All students, who's NOT wearing glasses, order by their LastName, displays ONLY their firstName and class

Multiple Select

Which operation is supported in a database query

• Selecting Records

• Selecting Fields

• Ordering

• Removing records