Rumah > Artikel > pangkalan data > 从MySQL数据库表中来检索数据并不难
我们今天主要和大家讲述的是如何正确的从MySQL数据库表中来检索相关数据的实际应用方案,如果你对MySQL数据库表中来检索相关数据的实际操作有兴趣的话,你就可以对以下的文章点击观看了。 1、从MySQL 数据库表中检索信息 实际上,前面我们已经用到了SELECT语
我们今天主要和大家讲述的是如何正确的从MySQL数据库表中来检索相关数据的实际应用方案,如果你对MySQL数据库表中来检索相关数据的实际操作有兴趣的话,你就可以对以下的文章点击观看了。
1、从MySQL 数据库表中检索信息
实际上,前面我们已经用到了SELECT语句,它用来从MySQL 数据库表中检索信息。
select语句格式一般为:
SELECT 检索关键词 FROM 被检索的表 WHERE 检索条件(可选)
以前所使用的“ * ”表示选择所有的列。
下面继续使用我们在上篇文章中创建的表mytable。
2、查询所有数据:
<ol class="dp-xml"> <li class="alt"><span><span>MySQL(和PHP搭配之最佳组合)</span><span class="tag">></span><span> select * from mytable; </span></span></li> <li><span>+----------+------+------------+----------+ </span></li> <li class="alt"><span>| name | sex | birth | birthaddr | </span></li> <li><span>+----------+------+------------+--------+ </span></li> <li class="alt"><span>| abccs |f | 1977-07-07 | china | </span></li> <li><span>| mary |f | 1978-12-12 | usa | </span></li> <li class="alt"><span>| tom |m | 1970-09-02 | usa | </span></li> <li><span>+----------+------+------------+----------+ </span></li> <li class="alt"><span>3 row in set (0.00 sec) </span></li> </ol>
3、修正错误记录:
假如tom的出生日期有错误,应该是1973-09-02,则可以用update语句来修正: MySQL(和PHP搭配之最佳组合)> update mytable set birth = "1973-09-02" where name = "tom";
再用2中的语句看看是否已更正过来。
4、选择特定行
上面修改了tom的出生日期,我们可以选择tom这一行来看看是否已经有了变化:
<ol class="dp-xml"> <li class="alt"><span><span>MySQL(和PHP搭配之最佳组合)</span><span class="tag">></span><span> select * from mytable where </span><span class="attribute">name</span><span> = </span><span class="attribute-value">"tom"</span><span>; </span></span></li> <li><span>+--------+------+------------+------------+ </span></li> <li class="alt"><span>| name |sex | birth | birthaddr | </span></li> <li><span>+--------+------+------------+------------+ </span></li> <li class="alt"><span>| tom |m | 1973-09-02 | usa | </span></li> <li><span>+--------+------+------------+------------+ </span></li> <li class="alt"><span>1 row in set (0.06 sec) </span></li> </ol>
上面WHERE的参数指定了检索条件。我们还可以用组合条件来进行查询:
<ol class="dp-xml"> <li class="alt"><span><span>MySQL(和PHP搭配之最佳组合)</span><span class="tag">></span><span> SELECT * FROM mytable WHERE </span><span class="attribute">sex</span><span> = </span><span class="attribute-value">"f"</span><span> AND </span><span class="attribute">birthaddr</span><span> = </span><span class="attribute-value">"china"</span><span>; </span></span></li> <li><span>+--------+------+------------+------------+ </span></li> <li class="alt"><span>| name |sex | birth | birthaddr | </span></li> <li><span>+--------+------+------------+------------+ </span></li> <li class="alt"><span>| abccs |f | 1977-07-07 | china | </span></li> <li><span>+--------+------+------------+------------+ </span></li> <li class="alt"><span>1 row in set (0.06 sec) </span></li> </ol>
5、 选择特定列
假如你想查看表中的所有人的姓名,则可以这样操作:
<ol class="dp-xml"> <li class="alt"><span><span>MySQL(和PHP搭配之最佳组合)</span><span class="tag">></span><span> SELECT name FROM mytable; </span></span></li> <li><span>+----------+ </span></li> <li class="alt"><span>| name | </span></li> <li><span>+----------+ </span></li> <li class="alt"><span>| abccs | </span></li> <li><span>| mary | </span></li> <li class="alt"><span>| tom | </span></li> <li><span>+----------+ </span></li> <li class="alt"><span>3 row in set (0.00 sec) </span></li> </ol>
如果想列出姓名和性别两列,则可以用逗号将关键词name和birth分开: myaql> select name,birth from mytable;
6、对行进行排序
我们可以对表中的记录按生日大小进行排序:
<ol class="dp-xml"> <li class="alt"><span><span>MySQL(和PHP搭配之最佳组合)</span><span class="tag">></span><span> SELECT name, birth FROM mytable ORDER BY birth; </span></span></li> <li><span>+----------+------------+ </span></li> <li class="alt"><span>| name | birth | </span></li> <li><span>+----------+------------+ </span></li> <li class="alt"><span>| tom | 1973-09-02 | </span></li> <li><span>| abccs | 1977-07-07 | </span></li> <li class="alt"><span>| mary | 1978-12-12 | </span></li> <li><span>+----------+------------+ </span></li> <li class="alt"><span>3 row in set (0.00 sec) </span></li> </ol>
我们可以用DESC来进行逆序排序:
<ol class="dp-xml"> <li class="alt"><span><span>MySQL(和PHP搭配之最佳组合)</span><span class="tag">></span><span> SELECT name, birth FROM mytable ORDER BY birth DESC; </span></span></li> <li><span>+----------+------------+ </span></li> <li class="alt"><span>| name | birth | </span></li> <li><span>+----------+------------+ </span></li> <li class="alt"><span>| mary | 1978-12-12 | </span></li> <li><span>| abccs | 1977-07-07 | </span></li> <li class="alt"><span>| tom | 1973-09-02 | </span></li> <li><span>+----------+------------+ </span></li> <li class="alt"><span>3 row in set (0.00 sec) </span></li> </ol>
7、 行计数
MySQL 数据库经常要统计一些数据,如表中员工的数目,我们就要用到行计数函数COUNT()。COUNT()函数用于对非NULL结果的记录进行计数:
<ol class="dp-xml"> <li class="alt"><span><span>MySQL(和PHP搭配之最佳组合)</span><span class="tag">></span><span> SELECT COUNT(*) FROM mytable; </span></span></li> <li><span>+----------+ </span></li> <li class="alt"><span>| COUNT(*) | </span></li> <li><span>+----------+ </span></li> <li class="alt"><span>| 3 | </span></li> <li><span>+----------+ </span></li> <li class="alt"><span>1 row in set (0.06 sec) </span></li> </ol>
员工中男女数量:
<ol class="dp-xml"> <li class="alt"><span><span>MySQL(和PHP搭配之最佳组合)</span><span class="tag">></span><span> SELECT sex, COUNT(*) FROM mytable GROUP BY sex; </span></span></li> <li><span>+------+----------+ </span></li> <li class="alt"><span>| sex | COUNT(*) | </span></li> <li><span>+------+----------+ </span></li> <li class="alt"><span>| f | 2 | </span></li> <li><span>| m | 1 | </span></li> <li class="alt"><span>+------+----------+ </span></li> <li><span>2 row in set (0.00 sec) </span></li> </ol>
注意我们使用了GROUP BY对SEX进行了分组。以上的相关内容就是对如何从 MySQL 数据库表中检索数据的介绍,望你能有所收获。