SQL databases store data in a tabular structure with each datum stored as a row. These rows need to be uniquely identified.
You can do so by using random unique numbers or alphanumeric combinations. You can also use a simple counting system where the first record is identified by a 1, the next 2, and so forth.
Most SQL databases will allow you to designate a column to not only store the unique identifier but also automatically generate the next one by "AUTOmatically incrementing" it.
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