CC SQL 1-introduction
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what is a database?
- 1. is acollection of data stored in some organized fashion.
- 2. a container (usally a file or set of files) to store organized data
a structured list of data of a specific type
information about database and table layout and properties
- Schema or Database? Occasionally schema is used as a synonym for database (and schemata as a synonym for databases). While unfortunate, it is usually clear from the context which meaning of schema is intended. In this book, schema will refer to the definition given here.
a single field in a table. All tables are made up of one or more columns
A type of allowed data. Every table column has associated datype that restricts (or allows) specific data in that column.
a column (or set of columns) whose values unquely identify every row in a table
- Any column in a table can be established as the primary key, as long as it meets the following conditions:
- 1. No two rows can have the same primary key value.
- 2. Every row must have a primary key value (primary key columns may not allow NULL values).
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