# [[Primary key]]
![[Primary key.svg]]
In [[Database|Databases]], a primary key is a unique identifier for a database record. This is most often a number so that it can be easily incremented while maintaining uniqueness, but strings (like filenames) could be used as primary keys as well.
In the `CUSTOMERS` table below, the `CustomerID` field is the most ideal primary key.
| CustomerID | Name | Address | Telephone Number |
| ---------- | ------------ | ------------------------------------- | ----------------- |
| 1 | John Doe | 123 Main St, London, UK | +44 20 7946 0958 |
| 2 | Jane Smith | 456 Elm St, Toronto, Canada | +1 416 555 1234 |
| 3 | Bob Johnson | 789 Oak St, Sydney, Australia | +61 2 9876 5432 |
| 4 | Alice Brown | 101 Pine St, Berlin, Germany | +49 30 1234 5678 |
| 5 | Charlie Lee | 222 Birch St, Tokyo, Japan | +81 3 5678 9012 |
| 6 | David White | 333 Cedar St, São Paulo, Brazil | +55 11 99876 5432 |
| 7 | Emily Clark | 444 Aspen St, Cape Town, South Africa | +27 21 345 6789 |
| 8 | Frank Adams | 555 Walnut St, Paris, France | +33 1 2345 6789 |
| 9 | Grace Miller | 666 Maple St, New Delhi, India | +91 11 9876 5432 |
| 10 | Henry Wilson | 777 Cherry St, Auckland, New Zealand | +64 9 876 5432 |
When a primary key of one table is referred to in another table, it is called a [[Foreign key]].
%%
# Excalidraw Data
## Text Elements
## Drawing
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%%