- Outer join: All data and intersection of the left (right) table of the left (right) outer join, the right (left) table field that does not meet the query conditions is replaced by null
-External connection: all data and intersection parts of the left (right) table of the left (right) external connection. The fields of the right (left) table that do not meet the query conditions are replaced by null
-outer join: all data and intersection parts of the left (right) table of the left (right) outer join, and the fields of the right (left) table that do not meet the query conditions are replaced by null.