Databases

Table

Databases are made up of tables. A table has columns called fields and rows called records. In IGCSE, databases only consist of a single table.

Fields are the different categories in a table which organise data belonging to the same group
Records are groups of data that often have a unique identifier
Validation is used to set rules for fields

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A table may have a header row to display the name of each field. A header row is not a record.

Data Types

Similar to programming, databases also have data types to enforce consistency and prevent errors. Different information can require different data types. It is important to be efficient and account for all possibilities when selecting a data type for a field.

Type	Example
Text & Alphanumeric	Names, Phone Numbers
Character	Gender
Boolean	True & False
Integer	Population
Real	Money
Date & Time	Date of Birth

Phone numbers are always a text field and not a numeric field!

Primary Key

A primary key is a field in a table that acts as a unique identifier for a record. For example, a number plate can be used to uniquely identify a car. Primary keys often have a specific format and are mostly named along the lines of ID.

SQL

SQL stands for Structured Query Language. It is used to fetch information from a database. Just like most programming languages, SQL has keywords. In IGCSE, only 6 keywords are used.

SELECT: chooses which fields to display (* means all fields)
FROM: points to the name of the table where the data can be found
WHERE: filters records using conditions
ORDER BY: sorts records in ascending order by default
SUM: calculates the total a field
COUNT: counts the number of records

SELECT field_1, field_2
FROM my_table
WHERE field_1 > 0 AND field_2 = "YES";