Many-to-many relationships in databases and their implementation

A record in thing a can correspond to more than one record in thing B, and a record in thing B can correspond to multiple records in thing A. For example: In a school, a class can have more than one classroom teacher, and a teacher can teach multiple classes. At this point, you can introduce a table C to simulate many-to-many relationships.

SQL statements:

--Class TableCreate TableBanji (banji_idint Primary Key, Banji_numint  not NULL, Banji_namenvarchar( -))--TeachersCreate TableJiaoshi (jiaoshi_idint Primary Key, Jiaoshi_namenvarchar( $))--The third table is used to simulate the relationship between class and teacher.Create Tablebanji_jiaoshi_mapping (banji_idint constraintfk_banji_idForeign Key ReferencesBanji (banji_id), jiaoshi_idint Foreign Key ReferencesJiaoshi (jiaoshi_id), Kechengnvarchar( -),    constraintpk_banji_id_jiaoshi_idPrimary Key(Banji_id,jiaoshi_id,kecheng))--Delete a tableDrop TableBanji_jiaoshi_mapping

Database diagram:

Note: This article refers to the Hao bin of the teacher's SQL tutorial, but also added some of their own understanding of SQL, there is a wrong place to write the hope that we can point out.

Many-to-many relationships in databases and their implementation