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Several concepts
- Cartesian product: one kind of set operations on the domain https://blog.csdn.net/wx13227855087/article/details/82704184
- Domain: a collection of the same data type.
- Relationship: Unable to accumulate data with Descartes, because a lot of tuples meaningless, meaningful out of it known as a tuple relations. So the relationship <Cartesian product. Relationship is a limited subset of the Cartesian product.
- Candidate code: a relation attribute uniquely identifies a set of tuples, but not a subset. If there are a plurality of candidate code relationship, wherein a code is selected based. Attribute candidate code called primary properties, properties not included in the candidate code in the code is called non-primary property or properties. If the candidate code contains all the attributes, it is called the full code.
- There are three types of relations: basic relationship (base table, group table), a lookup table, the table view.
- Mode is the type of relationship, the relationship is the value.
- Relational Database: A collection of a bunch of tables
Relational Operations
- Basic relational operations: result of the operation objects are set and
query: select, projection, is connected, in addition, and, cross, cross, Cartesian product
insert, delete, modify operation
Relational integrity
- Entity integrity: If A is the primary attribute property substantially relation R, then A can not take a null value (null), i.e. do not know / values / absence meaningless.
- Referential integrity: If the attribute (set) F R is the basic relationship of the outer code, and the master key K which substantially corresponds to the relationship S (basic relations R and S are not necessarily different relationships), the element for each of R group on the F value must be 1 or a null value (F value of each attribute are null) 2, or a value equal to the master key S of tuples.
- User-defined integrity: constraints for a specific database.
Relational algebra
- This blog written in very good shape: https://blog.csdn.net/Caoyang_He/article/details/81005144