MySQL join using () Usage

1 using () is used for join queries on two tables. The column specified by using () must exist in both tables and is used as the join condition. Example: select. *, B. * from a left join B using (colA); equivalent to: select. *, B. * from a left join B on. colA = B. colA;
2 Multi-table queries use multiple such joins. Example: select. *, B. * from a left join B using (colA) left join c using (colB); colA must exist in tables a and B, and colB in tables a and c.
In short, using () is short for specifying connection conditions in join, which is often used in simple connections. When the column names are different or the connection conditions are complex, it is more common to use a left join B on.