Oracle series: (13) Multi-table query
Multi-table query, including equivalent join, non-equivalent join, external join, self-join.
Internal connections, including equivalent connections and non-equivalent connections.
Cartesian set of employee table emp and department table dept (Cartesian set table = sum of columns, product of rows, some data in Cartesian table does not meet the requirements)
Select emp.ename,dept.dnamefrom emp,dept
Use equivalent / internal connections (only the = sign can be used) to display the employee's number, name, department name, and simplify using table aliases
Select emp.empno,emp.ename,dept.dname,dept.deptnofrom emp,deptwhere emp.deptno = dept.deptno
Use a non-equivalent connection (you cannot use the = sign, other symbols can, for example: > =
