賢者時間太久了麼？--MySQL繼續玩
1、MySQL
-----運算符和函數-----
字符函數，數值運算符，比較運算等
----字符函數
---
CONCAT()--字符連接
CONCAT_WS()--使用指定的分隔符進行字符連接
mysql> SELECT CONCAT('imooc','-','MySQL');
+-----------------------------+
| CONCAT('imooc','-','MySQL') |
+-----------------------------+
| imooc-MySQL |
+-----------------------------+
mysql> USE TEST;
Database changed
mysql> SELECT * FROM TEST;
+----+----------+
| id | username |
+----+----------+
| 1 | Tom |
| 2 | Ben |
+----+----------+
2 rows in set (0.02 sec)
mysql> SELECT CONCAT(id,username) AS fullname FROM test;
+----------+
| fullname |
+----------+
| 1Tom |
| 2Ben |
+----------+
以上是CONCAT()的實例，而CONCAT_WS()如下
mysql> SELECT CONCAT_WS('-',id,username) FROM test;
+----------------------------+
| CONCAT_WS('-',id,username) |
+----------------------------+
| 1-Tom |
| 2-Ben |
+----------------------------+
CONCAT_WS()需要至少三個參數，第一個是分隔符，後面才是需要連接的東西
---
FORMAT()，數字格式化
mysql> SELECT FORMAT(234234.23423,2);
+------------------------+
| FORMAT(234234.23423,2) |
+------------------------+
| 234,234.23 |
+------------------------+
就是標准化，當然是外國人那一套
---
LOWER()&UPPER()，大小寫變換
---
LEFT()&RIGHT()，獲取左右側字符
需要兩位參數,從哪個字段取，從第幾位開始的左右側
mysql> SELECT UPPER(LEFT('andy',1));
+-----------------------+
| UPPER(LEFT('andy',1)) |
+-----------------------+
| A |
+-----------------------+
---
LENGTH()，獲取字符串長度。注意，空格也要算在內
---
LTRIM(),RTRIM(),TRIM()，刪除前/後/前後的空格
TRIM還能刪除其他字符
mysql> SELECT TRIM(LEADING '!' FROM '!!!ANDY!!');
+------------------------------------+
| TRIM(LEADING '!' FROM '!!!ANDY!!') |
+------------------------------------+
| ANDY!! |
+------------------------------------+
1 row in set (0.00 sec)
mysql> SELECT TRIM(BOTH '!' FROM '!!!ANDY!!');
+---------------------------------+
| TRIM(BOTH '!' FROM '!!!ANDY!!') |
+---------------------------------+
| ANDY |
+---------------------------------+
1 row in set (0.00 sec)
mysql> SELECT TRIM(TRAILING '!' FROM '!!!ANDY!!');
+-------------------------------------+
| TRIM(TRAILING '!' FROM '!!!ANDY!!') |
+-------------------------------------+
| !!!ANDY |
+-------------------------------------+
1 row in set (0.00 sec)
---
REPLACE()
mysql> SELECT REPLACE('!!ANDY!SDL!!','!','');
+--------------------------------+
| REPLACE('!!ANDY!SDL!!','!','') |
+--------------------------------+
| ANDYSDL |
+--------------------------------+
1 row in set (0.00 sec)
mysql> SELECT REPLACE('!!ANDY!SDL!!','!','LALAL');
+-------------------------------------+
| REPLACE('!!ANDY!SDL!!','!','LALAL') |
+-------------------------------------+
| LALALLALALANDYLALALSDLLALALLALAL |
+-------------------------------------+
1 row in set (0.00 sec)
可以看到，替換是比較靈活的
---
SUBSTRING()
mysql> SELECT SUBSTRING('MYSQL','1','2');
+----------------------------+
| SUBSTRING('MYSQL','1','2') |
+----------------------------+
| MY |
+----------------------------+
1 row in set (0.00 sec)
注意mysql是從1開始，不是從0開始數數
---
做匹配
mysql> SELECT 'mysql' LIKE 'M%';
+-------------------+
| 'mysql' LIKE 'M%' |
+-------------------+
| 1 |
+-------------------+
1 row in set (0.00 sec)
mysql> SELECT * FROM test WHERE username LIKE '%m%';
+----+----------+
| id | username |
+----+----------+
| 1 | Tom |
+----+----------+
這裡，%代表任意，類似window中的*
_代表任意一個字符
----數值運算符以及函數
幾個很通用的函數簡單的介紹下
CEIL()-向上取整---------FLOOR()-向下取整
DIV()-整數除法，也就是結果只有整數
MOD()-取余數
POWER()-冪運算
ROUND()-四捨五入
TRUNCATE()-數字截取（不再四捨五入）
不是兩位參數，就是一位參數，大家自己試試哈
----比較運算符與函數
---
[NOT] BETWEEN...AND...
mysql> SELECT 123 BETWEEN 2 AND 123123;
+--------------------------+
| 123 BETWEEN 2 AND 123123 |
+--------------------------+
| 1 |
+--------------------------+
---
[NOT] IN()，給定幾個區間來做判斷
mysql> SELECT 123 IN(123,23,12);
+-------------------+
| 123 IN(123,23,12) |
+-------------------+
| 1 |
+-------------------+
1 row in set (0.00 sec)
mysql> SELECT 123 IN(120,23,12);
+-------------------+
| 123 IN(120,23,12) |
+-------------------+
| 0 |
+-------------------+
---
IS [NOT] NULL,判斷是空麼
mysql> SELECT 0 IS NULL;
+-----------+
| 0 IS NULL |
+-----------+
| 0 |
+-----------+
常用在檢查是否為空
mysql> SELECT * FROM test WHERE username IS NULL;
Empty set (0.00 sec)
----日期時間函數
---
NOW()，返回當時的日期和時間
CURDATE(),CURTIME()
---
DATE_ADD()，當前日期的變化
mysql> SELECT DATE_ADD('2012-2-23', INTERVAL 234 DAY);
+-----------------------------------------+
| DATE_ADD('2012-2-23', INTERVAL 234 DAY) |
+-----------------------------------------+
| 2012-10-14 |
+-----------------------------------------+
1 row in set (0.00 sec)
mysql> SELECT DATE_ADD('2012-2-23', INTERVAL -234 DAY);
+------------------------------------------+
| DATE_ADD('2012-2-23', INTERVAL -234 DAY) |
+------------------------------------------+
| 2011-07-04 |
+------------------------------------------+
1 row in set (0.00 sec)
---
DATEDIFF()，得到兩個日期間的差值
mysql> SELECT DATEDIFF('2304-2-2','1234-3-22');
+----------------------------------+
| DATEDIFF('2304-2-2','1234-3-22') |
+----------------------------------+
| 390760 |
+----------------------------------+
1 row in set (0.02 sec)
---
DATE_FORMAT()，日期的格式化，日期的格式是可以選的，也就是說日期的格式轉換
mysql> SELECT DATE_FORMAT('2013-2-22','%m/%d/%y');
+-------------------------------------+
| DATE_FORMAT('2013-2-22','%m/%d/%y') |
+-------------------------------------+
| 02/22/13 |
+-------------------------------------+
1 row in set (0.00 sec)
----信息函數
USER(),VERSION(),DATEBASE(),CONNECTION_ID(),LAST_INSERT_ID()
----聚合函數
只有一個返回值是他們的特點
AVG(),COUNT(),MAX(),MIN(),SUM()
直接調用可能會有錯誤，一般是針對數據表的字段進行的操作
mysql> SELECT AVG(id) FROM test;
+---------+
| AVG(id) |
+---------+
| 1.5000 |
+---------+
----加密函數
MD5(),PASSWORD()
mysql> SELECT MD5('HELLOWORLD');
+----------------------------------+
| MD5('HELLOWORLD') |
+----------------------------------+
| e81e26d88d62aba9ab55b632f25f117d |
+----------------------------------+
1 row in set (0.00 sec)
mysql> SELECT PASSWORD('HELLOWORLD');
+-------------------------------------------+
| PASSWORD('HELLOWORLD') |
+-------------------------------------------+
| *3456E7782A7F539BC823C715DB60231B0C7DE847 |
+-------------------------------------------+
1 row in set (0.00 sec)
一般而言，網頁的編程用的都是MD5，password僅僅用於修改當前用戶的密碼
----
注重自帶函數的熟悉、了解，靈活的調用和嵌套運用
