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Paper 2: Databases | O Level Computer Science 2210 & IGCSE Computer Science 0478 | Detailed Free Notes To Score An A Star (A*)

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  • Database
    • Collection of data
    • It has different tables
    • Each table has many different fields
      • Each field is a column with specific types of data
      • Each field has many different records
        • A record is one row in the database
  • Data Types
    • Text/ Alphanumeric
      • Combination of letters, numbers and symbols
      • Numbers are treated as text here so they can’t be added or subtracted directly
      • Speech marks are used around them
    • Character
      • A single number or character
      • Numbers are still used as text
    • Boolean
      • Has two options
        • Like true false
        • No speech marks
    • Integer
      • A whole number
    • Real
      • A number with at least one decimal place
    • Date/ Time
      • A date or/and time
  • Primary Key
    • One unique field in the database
    • It will not appear twice in any record
    • For example, CNIC number can be a primary key in a table that is focused on details of people
    • First name and last name in this case are not suitable choice because many people can have the same first name and last name
  • SQL
    • Structured Query Language
    • Important for paper
    • It is used to perform actions such as define tables, change tables, add data, search data (main focus of exams) and perform calculations within tables.
  • SELECT … FROM
    • It allows you to select a field or set of fields form the table
    • SELECT field
    • FROM table
    • For example
      • SELECT BookName
      • FROM Books
      • It will select Book Name column (field) from the Books table
    • If more than one selection, we can use a comma between them i.e. SELECT BookName, Genre (two fields selected
  • SELECT FROM WHERE
    • Including where will allow selection of only specific data
    • Here, we can use logical operators
      • = equal to
      • < less than
      • <= less than equal to
      • > greater than
      • >= greater than equal to
      • <> Not equal to
    • For example
      • SELECT FirstName, LastName, Posted
      • FROM Orders
      • WHERE Posted = Yes
      • Only the first names, last names and posted information from orders table will be selected where posted has a value of yes. Any record with posted value as no won’t be selected.
  • More than one condition
    • We use BOOLEAN Operators
      • AND
        • Both conditions must be true
      • OR
        • Any one condition or both conditions must be true
    • No comma between the conditions just the logical operator
      • WHERE Condition 1 BOOLEAN Condition 2
  • Selecting values in or not in a condition
    • It is not necessary to also select the field that we use in the condition
    • For example
      • SELECT FirstName, LastName
      • FROM Orders
      • WHERE Posted = Yes
      • Although we didn’t select the field of POSTED for display, we can still run a condition on it
  • Order by
    • We can use this to order the data ascending or descending
    • ORDER BY field name and then ASC or DESC
    • The order field can be different from the ones we have selected
  • SUM
    • SELECT Sum (field)
    • FROM table
    • We can also put a condition with WHERE
    • It will provide the added total of the field
  • COUNT
    • Select COUNT (field)
    • FROM table
    • Where for condition
Hunain Zia

Hunain Zia has previously achieved considerable success in the high-school educational stream, gaining a massive 154 Total A Grades and 7 Major Distinctions, a process in which he broke/ set 11 different world records, including the most A grades ever achieved, most subjects ever appeared in, most distinctions, gaining distinctions across two separate boards (Pearson Edexcel and CAIE) within the same year/ ever, and even 19 hours of constant examination. All records stand intact today. Hunain pursued his Honors Accounting Degree from the prestigious Bentley University, and then completed an LLB (in Honors) from University of London. Currently, he manages multiple social and commercial projects, has founded digital streams and works tirelessly in the education sector.

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