http://www.cnblogs.com/renpei/p/5485730.html
http://database.51cto.com/art/201010/229082.htm
mysql> select *from lee;
+-------+----------+
| name | birthday |
+-------+----------+
| test | 1984 |
| siyu | 1988 |
+-------+----------+
2 rows in set (0.00 sec)
mysql> select name, birthday, case when birthday>'1984' then 'yong' when birthday<'1985' then 'old' else 'ok' end YORN from lee;
+-------+----------+------+
| name | birthday | YORN |
+-------+----------+------+
| test | 1984 | old |
| siyu | 1988 | yong |
+-------+----------+------+
2 rows in set (0.00 sec)
SELECT
case -------------如果
when sex='1' then '男' -------------sex='1'，则返回值'男'
when sex='2' then '女' -------------sex='2'，则返回值'女'
else
0 -------------其他的返回'其他’
end -------------结束
from
sys_user --------整体理解： 在sys_user表中如果sex='1'，则返回值'男'如果sex='2'，则返回值'女' 否则返回'其他’
http://w3resource.com/mysql/advance-query-in-mysql/join-using-group-by.php
SELECT bk1.book_name,bk1.pub_lang,bk1.book_price
FROM book_mast bk1
JOIN(SELECT pub_lang,MAX(book_price) AS price
FROM book_mast
GROUP BY pub_lang) AS bk2
ON bk1.pub_lang=bk2.pub_lang AND bk1.book_price=bk2.price;
mysql join group
http://w3resource.com/mysql/advance-query-in-mysql/mysql-cross-join.php
http://kccoder.com/mysql/join-group-by-performance/
SELECT 20170613 as ymd, b.uid,b.ip FROM (SELECT uid FROM `stat_online_uid_qid_temp` ORDER BY uid ASC LIMIT 0,10) a LEFT JOIN `stat_online_uid_qid_temp` b ON a.uid=b.uid
mysql> select *from Store_Information;
+-------------+-------+-------------+
| Store_Name | Sales | Txn_Date |
+-------------+-------+-------------+
| Los Angeles | 1500 | Jan-05-1999 |
| San Diego | 250 | Jan-07-1999 |
| Los Angeles | 300 | Jan-08-1999 |
| Boston | 700 | Jan-08-1999 |
+-------------+-------+-------------+
4 rows in set (0.00 sec)
mysql> select count(distinct Store_Name) as online from Store_Information;
+--------+
| online |
+--------+
| 3 |
+--------+
1 row in set (0.00 sec)
mysql> SELECT count(*) as `online` from (SELECT Store_Name FROM `Store_Information` group by Store_Name) as a;
+--------+
| online |
+--------+
| 3 |
+--------+
1 row in set (0.00 sec)
mysql>
http://kccoder.com/mysql/join-group-by-performance/
http://www.w3school.com.cn/sql/sql_join.asp
http://www.1keydata.com/sql/inner-join.html
http://www.cnblogs.com/pcjim/articles/799302.html
http://www.1keydata.com/sql/sqljoins.html
http://www.java2s.com/Tutorial/MySQL/0100__Table-Join/Updateleftjoins.htm
