SQL高级查询之一

一，子查询

SELECT e.emp_id, e.fname, e.lname FROM (SELECT emp_id, fname, lname, start_date, title FROM employee ) e;

二，从视图中查询

CREATE VIEW employee_vw AS
    -> SELECT emp_id, fname, lname,
    -> YEAR(start_date) start_year
    -> FROM employee;

SELECT emp_id, start_year
    -> FROM employee_vw;

三，联表查询

SELECT e.emp_id, e.fname,  e.lname, d.name dept_name FROM employee AS e INNER JOIN department AS d ON e.dept_id = d.dept_id;

四，WHERE子句配逻辑表达式

SELECT emp_id, fname, lname, start_date, title FROM employee WHERE title = 'Head Teller' OR start_date > '2002-01-01';

五，GROUP BY子句配合HAVING使用

SELECT d.name, count(e.emp_id) num_employees FROM department d INNER JOIN employee e ON d.dept_id = e.dept_id GROUP BY d.name HAVING count(e.emp_id) > 2;

六，ORDER BY排序使用内置函数

SELECT cust_id, cust_type_cd, city, state, fed_id FROM customer ORDER BY RIGHT(fed_id, 3) DESC;