Oracle Oracle's internal and external connections

internal and external connections in the 1,oracle

1, internal connection

The internal connection is that the qualifying data is selected and the data that is not eligible is filtered out.

1,1,1 equivalent Connection

First look at the "s_emp" table structure you need to use:

1 Tablename:s_emp2 Name Description3 ------------------  -------------4 ID Employee Number5 last_name name6 first_name Surname7 USERID ID Number8 start_date Start Time9 COMMENTS Comment ContentTen manager_id Superior Number One Title Caption A dept_id Department Number - SALARY Salary -Commission_pct Commission

s_emp table (Employee table) structure

1 Table name:s_dept 2 Name                Description3------------------  -------------4ID                  Department number  5name                Department 6 region_id           area number

s_dept table (Employee table) structure

Query each employee's number last name Department name

Select e.id,e.first_name,d.name          from s_emp e,s_dept D                where e.dept_id=d.id;

1,2,1 Non-equivalent connection

1,3,1 Self-connect

External connections

1,2,1 equivalent Connection

1,2,2 Non-equivalent connection

Self-connect

internal and external connection of 2,sql99

2,1 SQL99 Internal Connection

2.2 SQL99 External Connection

Oracle Oracle's internal and external connections