1. Equijoin query
2. Unequal value join
3. Outer connection: You can query data that does not meet the connection conditions ※: Pay attention to the difference
4. Self-inquiry
5. Inner join only returns data that satisfies the connection conditions
6. Left join returns the data that satisfies the join condition and the data that does not satisfy the condition on the left
7. Right join Returns the data that satisfies the join condition and the data that does not satisfy the condition on the right
