Oracle database, join multi-Table Association, union result set Merge

Join on: Multi-Table Association

Internal connections: Connecting to other tables

From table 1 T  join table 2 s on  t. Field 1 =s. field 2  join table 3 N on N. field 3=t. field 1 or from table 1 A, table 2 B, table 3c  where a. field =b. field

　　

Self-connect: connect to itself

From table 1 T  join table 1 s on  t. Field 1 =s. field 1  S. field 1=t. Field 1

Outer connection: Left/Right connection

     the LEFT join   is guaranteed that the data on the left side of the table shows all the    right joins  on the starboard join to ensure that the data on the right table is displayed

　　

Full connection: Ensure that the data on both sides of the table appears

Full join on

　　

Union: Result set Merge

Requirement: The number of columns and field types of the data should be consistent

Cases:

Select S.name,s.sex,t.cno from student sunionselect t.name,t.sex,t.cno from student t   remove duplicate data and merge Select S.name,s.sex,t.cno from student sunion  allselect t.name,t.sex,t.cno from student t   remove duplicate data and merge

　　

Oracle database, join multi-Table Association, union result set Merge