多表查询

1.SELECT*FROM dept,emp WHERE dept.dept1=emp.dept2;SELECT SUM(incoming) FROM(SELECT*FROM dept,emp WHERE dept.dept1=emp.dept2);
2.SELECT sid FROM dept LEFT JOIN emp ON dept.dept1=emp.dept2 WHERE dept1=103;
3.SELECT MAX(age),name,dept_name RIGHT JOIN dept ON dept.dept1=emp.dept2 GROUP BY dept_name;
4.SELECT SUM(incoming),dept_name RIGHT JOIN dept ON dept.dept1=emp.dept2 GROUP BY dept_name;
5.SELECT dept_name FROM dept RIGHT JOIN emp  ON dept.dept1=emp.dept2 WHERE incoming>7000;
6.SELECT dept_name FROM dept LEFT JOIN emp ON dept.dept1=emp.dept2 WHERE worktime_start is null;