1. Connection query Reference: MySQL
The significance of connection query: When the user views the data, the data to be displayed comes from multiple tables.
(1) Internal connection query is the most common connection query. Internal connection query can query two or more tables
- Inner join: [inner] join : Take each record from the left table and go to the right table to match with all records: The match must be that a certain condition is the same in the left table and the right table before the result is retained, otherwise Not Retained.
