X.P.Chen

摘要： CASE WHEN employee.title='Head Teller' THEN 'Head Teller' WHEN employee.title='Teller' AND YEAR(employee.start_date)>2007 THEN 'Teller TRAINEE' WHEN employee.title='Teller' AND YEAR(employee.start_date)<2006 THEN 'Experienced Teller' WHEN employe 阅读全文

摘要： Learning SQL2一 分组与聚集聚集函数--GROUNP BYmysql> SELECT gender,COUNT(*) how_many -> FROM student_list -> GROUP BY gender;+--------+----------+| gender | how_many |+--------+----------+| F | 2 || M | 2 |+--------+----------+聚集函数MAX() 返回集合中的最大值MIN() 返回集合中的最小值AVG() 返回集合中的平均值SUM() 返回集合中所... 阅读全文

摘要： Learning SQL --集合操作A+B A union BAB A intersect BA-B A except B1.union intersect exceptSELECT id,genderFROM student_listUNION ALLSELECT id,foodFROM favorite_food;UNION 去除重复项，union保留重复项 阅读全文

摘要： Learning SQL --多表查询1.笛卡尔积SELECT e.fname,e.lname,d.nameFROM employee e JOIN department d;2.内连接SELECT e.fname,e.lname,d.nameFROM employee e JOIN department dON e.dept_id=d.dept_id;==SELECT e.fname,e.lname,d.nameFROM employee e INNER JOIN department dON e.dept_id=d.dept_id;==SELECT e.fname,e.lname,d.na 阅读全文

摘要： 在学习SQL中在LEARNING SQL中摘录的笔记Learning SQL1.去除重复的行SELECT DISTINCT cust_idFROM account;2.子查询根据其他查询再设置查询SELECT e.emp_id,e.name,e.lnameFROM (SELECT emp_id,fname,lname,start_date,titleFROM employee) e;3.升序或降序排列关键字：asc(升) desc(降)ORDER BY student_id DESC;4.根据表达式排序RIGHT LEFTORDER BY RIGHT(fed_id,3) 按最后三位数字排序5. 阅读全文