Shulou(Shulou.com)06/01 Report--

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: > =

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