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2 - 2 Data Manipulation

Data reference (i.e., extraction) from the database is the most widely-used data manipulation. In SQL, use the SELECT statement for referring to data. The explanation provided here is mainly focused on the method of using the SELECT statement.

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2-2-1 Reference Without Specifying Conditions

Reference without specifying conditions corresponds to the relational operation “Projection” that extracts the specified attributes. Use the following SELECT statement in reference without specifying conditions.

ex06: Extract all columns from the “Student” table.

ex07: Extract Gender from the “Student” table. (Projection).

ex08: Extract Gender from the “Student” table after duplication is eliminated. (Projection)