What are the relational operations unique to relational databases?

The unique relational operations of relational databases include: 1. Selection operation, which selects those records that meet the specified conditions from all records in the two-dimensional relational table; 2. Projection operation, selects from all fields Operate on some fields and their values, which is a vertical operation; 3. Join operation, perform a projection operation on two relationships to join and generate a new relationship.

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The relational database system has three specialized relational operations.

1) Selection operation: Select those tuples that meet the limiting conditions from the given relationship.

2) Projection operation: Select the specified attribute group from all attributes of the given relationship in the required order.

3) Join operation: Splice the attribute names of two different relationships into a large relationship pattern. The attribute values ​​with the same nature in the two relationships should meet the limiting conditions. The new tuples after splicing these tuples The groups collectively form a new relationship after the join.

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