Mysql 函數(shù)
日期計算
MySQL提供了幾個函數(shù)履肃，可以用來計算日期偏灿，例如，計算年齡或提取日期部分走孽。
要想確定每個寵物有多大惧辈，可以計算當前日期的年和出生日期之間的差。如果當前日期的日歷年比出生日期早磕瓷，則減去一年盒齿。以下查詢顯示了每個寵物的出生日期、當前日期和年齡數(shù)值的年數(shù)字困食。
mysql> SELECT name, birth, CURDATE(),
-> (YEAR(CURDATE())-YEAR(birth))
-> - (RIGHT(CURDATE(),5)<RIGHT(birth,5))
-> AS age
-> FROM pet;
+----------+------------+------------+------+
| name | birth | CURDATE() | age |
+----------+------------+------------+------+
| Fluffy | 1993-02-04 | 2003-08-19 | 10 |
| Claws | 1994-03-17 | 2003-08-19 | 9 |
| Buffy | 1989-05-13 | 2003-08-19 | 14 |
| Fang | 1990-08-27 | 2003-08-19 | 12 |
| Bowser | 1989-08-31 | 2003-08-19 | 13 |
| Chirpy | 1998-09-11 | 2003-08-19 | 4 |
| Whistler | 1997-12-09 | 2003-08-19 | 5 |
| Slim | 1996-04-29 | 2003-08-19 | 7 |
| Puffball | 1999-03-30 | 2003-08-19 | 4 |
+----------+------------+------------+------+
模式匹配
MySQL提供標準的SQL模式匹配边翁，以及一種基于象Unix實用程序如vi****、****grep和sed的擴展正則表達式模式匹配的格式硕盹。
SQL模式匹配允許你使用“_”
匹配任何單個字符符匾，而“%”
匹配任意數(shù)目字符(包括零字符)。在MySQL中瘩例，SQL的模式默認是忽略大小寫的啊胶。下面給出一些例子甸各。注意使用SQL模式時，不能使用=或!=焰坪；而應使用LIKE或NOT LIKE比較操作符趣倾。
要想找出以“b”開頭的名字：
mysql> SELECT * FROM pet WHERE name LIKE 'b%';
+--------+--------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+--------+--------+---------+------+------------+------------+
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
| Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 |
+--------+--------+---------+------+------------+------------+
要想找出以“fy”結(jié)尾的名字：
mysql> SELECT * FROM pet WHERE name LIKE '%fy';
+--------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+--------+--------+---------+------+------------+-------+
| Fluffy | Harold | cat | f | 1993-02-04 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+--------+--------+---------+------+------------+-------+
要想找出包含“w”
的名字：
mysql> SELECT * FROM pet WHERE name LIKE '%w%';
+----------+-------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+----------+-------+---------+------+------------+------------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 |
| Whistler | Gwen | bird | NULL | 1997-12-09 | NULL |
+----------+-------+---------+------+------------+------------+
要想找出正好包含5個字符的名字豆拨，使用“_”
模式字符：
mysql> SELECT * FROM pet WHERE name LIKE '_____';
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+
由MySQL提供的模式匹配的其它類型是使用擴展正則表達式超陆。當你對這類模式進行匹配測試時，使用REGEXP和NOT REGEXP操作符(或RLIKE和NOT RLIKE黄刚，它們是同義詞)黔漂。
為了說明擴展正則表達式如何工作诫尽，下面使用REGEXP重寫上面所示的LIKE查詢：
為了找出以“b”開頭的名字，使用“^”匹配名字的開始：
mysql> SELECT * FROM pet WHERE name REGEXP '^b';
+--------+--------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+--------+--------+---------+------+------------+------------+
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
| Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 |
+--------+--------+---------+------+------------+------------+
如果你想強制使REGEXP比較區(qū)分大小寫瘟仿，使用BINARY關(guān)鍵字使其中一個字符串變?yōu)槎M制字符串箱锐。該查詢只匹配名稱首字母的小寫‘b’。
mysql> SELECT * FROM pet WHERE name REGEXP BINARY '^b';
為了找出以“fy”
結(jié)尾的名字劳较，使用“$”
匹配名字的結(jié)尾：
mysql> SELECT * FROM pet WHERE name REGEXP 'fy$';
+--------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+--------+--------+---------+------+------------+-------+
| Fluffy | Harold | cat | f | 1993-02-04 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+--------+--------+---------+------+------------+-------+
為了找出包含一個“w”
的名字驹止，使用以下查詢：
mysql> SELECT * FROM pet WHERE name REGEXP 'w';
+----------+-------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+----------+-------+---------+------+------------+------------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 |
| Whistler | Gwen | bird | NULL | 1997-12-09 | NULL |
+----------+-------+---------+------+------------+------------+
既然如果一個正則表達式出現(xiàn)在值的任何地方，其模式匹配了观蜗，就不必在先前的查詢中在模式的兩側(cè)放置一個通配符以使得它匹配整個值臊恋，就像你使用了一個SQL模式那樣。
