Basic knowledge of database design

• Relationship Editor

 1. Relationship Type
           mysql  Data table relationships : 
            First of all ：1 Yes 1  The relationship between （1：1）.
		    second ：1 Relationship to many （1：n）.
            Third ： many-to-many （m：n）.
Identifying relationship ( Identify relationships )   and  non-Identifying relationship( Unrecognized relationship ) ;  The former is mandatory , Rely on the , The latter is optional , Independent 
 2. Existence
      M/O(Mandatory or Optional)： “Mandatory” Indicates that this query field is required ;“Optional” Indicates that this query field is optional .
 3. Cardinality
       One to many relationship ,  It is usually used Mandatory Of . such as , The relationship between birthplace and people . People must have a place of birth (not null).
 among , Divide again 1 Yes 0..*(One to Zero or More), 1 Yes 1..*(One to One or More), 1 Yes 0..1(One to Zero or One),
1 Yes n(One to Exactly)

 But in some cases optional, For example, the relationship between nationality and people . People can have no nationality ( It can be for null), But if you have nationality , You must choose from the list of nationalities , May have a nationality , You can also have multiple nationalities 

 Many to many relationship ,  use Non-Specific,  What intermediate tables will be automatically generated when generating tables ,  Degrade into 2 Many to one relationship