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Cambridge IGCSE Computer Science · 0478
Topic 9: Databases — Part 4
SQL Commands
SQL commands
SQL (Structured Query Language) is used to retrieve and analyse data stored in a database. The main commands you need to know for Cambridge IGCSE are:
| Command / keyword | Purpose |
|---|---|
| SELECT | Identifies the specific fields (columns) to be retrieved |
| FROM | Identifies the table being queried |
| WHERE | Sets the specific conditions for the search |
| ORDER BY | Sorts the results based on a specified field |
| ASCENDING | Sorts records from lowest to highest (A→Z, 0→9) |
| DESCENDING | Sorts records from highest to lowest (Z→A, 9→0) |
| SUM | Aggregate function that adds up all values in a numeric field |
| COUNT | Aggregate function that counts records meeting a condition |
| AND | Combines conditions in WHERE — both must be true for a record to match |
| OR | Combines conditions in WHERE — either condition can be true for a record to match |
| * (wildcard) | Used with SELECT to return all attributes (fields) |
A typical query follows this order: SELECT fields FROM table WHERE condition ORDER BY field ASCENDING or DESCENDING. Use AND when every condition must match; use OR when any one condition is enough.
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