Data-Definition Language Commands

Data-Definition Language Commands

The second type of command is the simpler to process, and we show its trail beginning at the upper right side of following figure. For example, the database administrator, or DBA, for a university registrar's database might decide that there should be a table or relation with columns for a student, a course the student has taken, and a grade for that student in that course. The DBA might also decide that the only permissible grades are A, B, C, D, and F. This structure and constraint information is all part of the diagram of the database. It is shown in following figure as entered by the DBA, who needs special authority to execute schema-altering commands, since these can have deep effects on the database. These schema-altering DDL commands ("DDL" stands for "data-definition language") are parsed by a DDL processor and passed to the execution engine, which then goes through the index/file/record manager to alter the metadata, that is, the schema information for the database.

Data-Definition Language Commands



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