SQL And Databases

A database is an organised collection of data that can be easily accessed, managed, and updated.

A record is a single row in a table that contains data about one item.

A field is a column in a table that holds one piece of data about every record.

A primary key is a field that uniquely identifies each record in a table. It cannot be duplicated or left empty.

A foreign key is a field in one table that links to the primary key in another table, creating a relationship between the tables.

A database that stores all data in a single table. It is simple but can lead to data redundancy.

A database that stores data in multiple related tables, reducing redundancy and improving data integrity.

SQL (Structured Query Language) is the standard language used to create, modify, and query databases.

It retrieves data from a database. Example: SELECT name FROM students returns the name field from the students table.

It filters results based on a condition. Example: SELECT * FROM students WHERE grade = ‘A’ returns only students with grade A.

It means “select all fields”. Example: SELECT * FROM students returns every column from the students table.

Use ORDER BY. Example: SELECT name FROM students ORDER BY age sorts by age.

Use AS. Example: SELECT name AS student_name FROM students.

It adds new data to a table. Example: INSERT INTO students (name, grade) VALUES (‘Alice’, ‘A’).

It changes existing data. Example: UPDATE students SET grade = ‘B’ WHERE name = ‘Alice’.

It removes data from a table. Example: DELETE FROM students WHERE name = ‘Alice’.

Validation checks that data entered is sensible and reasonable, improving data integrity and reducing errors.