Select score.name, event.date, score.score.score, event.typeform score, eventwhere evenet.date = "1990-09-23" and score.event_id = event.event_id
In the connection query, the connection query of the three tables is done by two identical columns.
The meaning of the connection query is to meet the same original group of three tables in parallel, just choose to output that column. The main construction here determines the relationship between two tables. The more columns, the same columns in three tables will be rare.
Create Table Student (Name Varchar (20) Not NULL, SEX ENUM ('f', 'm') Not null, student_id int unsigned NUT NULL Auto_Increment primary key
This sentence is worth memory is the default selection, the keyword, and the last primary constraint varchar is a variant of the maximum change value. ENUM is an enumeration type.
P R I M a RY Key indicates that the value of the corresponding column is a quick lookup for indexing, and each value in the column must be unique. This prevents the I D of the same name to appear twice, which is a must-have characteristic for the student ID number. (Not only that, but mysql also requires each Au to_increment column to have a unique index.) If you don't understand the meaning of Au to_increment and prima ry key, as long as it is imagined as a magic method for each student I.e. In addition to the required value, there is nothing else.
