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This article mainly introduces the relational operation of the database, which has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, let the editor take you to understand it.

The relational operation of the database includes: (1) selection operation, selecting all tuples that meet the given conditions from a relation R; (2) projection operation, selecting some specified attributes from all attributes of a relation R; and (3) join operation. It is to select tuples that meet certain conditions from the generalized Cartesian product of two relations to form a new relationship.

The relational operations of the database include:

1. Selection operation to select all tuples that meet a given condition from a relation R

2. Projection operation to select some specified attributes from all attributes of a relation R.

3. Join operation is to select tuples that satisfy certain conditions from the generalized Cartesian product of two relations to form a new relationship.

Knowledge expansion:

1. Traditional set operation

1. UNION has two relations R and S, which have the same structure. The union of R and S is a set of tuples belonging to R or S, and the operator is ∪. Write it down as Tanner R ∪ S.

2. The difference between DIFFERENCE R and S is a set of tuples that belong to R but not S, and the operator is -. Record it as T=R-S.

3. The intersection of (INTERSECTION) R and S is a set of tuples belonging to both R and S, and the operator is ∩. Write it down as Tanner R ∩ S. R ∩ Shear R-(Rmurs).

2. Selection operation

Finding those tuples from a relationship that meet a given condition is called selection. The conditions are given in logical expressions, and tuples with true values are selected. This operation extracts tuples from the horizontal direction. The phrases FOR and WHILE in FOXPRO are equivalent to selection operations.

For example: LIST FOR publisher = 'higher Education Press' AND unit price

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