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Some notes of MySQL
2022-07-06 11:00:00 【Sanli akaman】
Three paradigms of database
First normal form : emphasize
The atomicity of a field
, The meaning of a field is indivisible , Accurately express the meaning of its field ;Second normal form : emphasize
Uniqueness of records
, A primary key can uniquely identify a data , No redundant data ;surface : Student number 、 The student's name 、 Course 、 credits
Third normal form : emphasize
Redundancy of fields
, Any field of a table cannot be derived from other fields , The required field is not Rongyou , namely There is no transitive relationship ;surface : Student number 、 full name 、 Age 、 The name of the College 、 College phone ;
- There are transitive dependencies , Student number -> Student -> My college -> College phone
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