SQL is more than just a means for extracting knowledge from data. It’s also a language for defining the structures that hold data so we can organize relationships in the data. Chief among those structures is the table.

A table is a grid of rows and columns that store data. Each row holds a collection of columns, and each column contains data of a specified type: most commonly, numbers, characters, and dates. We use SQL to define the structure of a table and how each table might relate to other tables in the database. We also use SQL to extract, or query, data from tables.

Understanding tables is fundamental ...

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