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数据库的操作总结就是：增删改查(CURD),今天记录一下基础的检索查询工作。
检索MySQL
1.查询表中所有的记录
mysql> select * from apps;
+----+------------+-----------------------+---------+
| id | app_name | url | country |
+----+------------+-----------------------+---------+
| 1 | QQ APP | http://im.qq.com | CN |
| 2 | 微博 APP | http://weibo.com | CN |
| 3 | 淘宝 APP | http://www.taobao.com | CN |
+----+------------+-----------------------+---------+
3 rows in set (0.00 sec)
2. 查询表中某列(单列)的记录
mysql> select app_name from apps;
+------------+
| app_name |
+------------+
| QQ APP |
| 微博 APP |
| 淘宝 APP |
+------------+
3 rows in set (0.00 sec)
3.检索表中多列的记录,列名之间用逗号分开
mysql> select id, app_name from apps;
+----+------------+
| id | app_name |
+----+------------+
| 1 | QQ APP |
| 2 | 微博 APP |
| 3 | 淘宝 APP |
+----+------------+
3 rows in set (0.00 sec)
4.检索不重复的记录，distinct关键字
mysql> select * from apps;
+----+------------+-----------------------+---------+
| id | app_name | url | country |
+----+------------+-----------------------+---------+
| 1 | QQ APP | http://im.qq.com | CN |
| 2 | 微博 APP | http://weibo.com | CN |
| 3 | 淘宝 APP | http://www.taobao.com | CN |
| 4 | QQ APP | http://im.qq.com | CN |
+----+------------+-----------------------+---------+
4 rows in set (0.00 sec)
上面表中是所有的数据，可以看到第1条和第4条数据是一样的，如果想要检索时不想出现重复的数据，可以使用distinct关键字，并且需要放在所有列的前面
mysql> select distinct app_name from apps;
+------------+
| app_name |
+------------+
| QQ APP |
| 微博 APP |
| 淘宝 APP |
+------------+
3 rows in set (0.00 sec)
5.限制检索记录的数量， limit关键字
mysql> select * from apps limit 2;
+----+------------+------------------+---------+
| id | app_name | url | country |
+----+------------+------------------+---------+
| 1 | QQ APP | http://im.qq.com | CN |
| 2 | 微博 APP | http://weibo.com | CN |
+----+------------+------------------+---------+
2 rows in set (0.00 sec)
limit后面可以跟两个值, 第一个为起始位置, 第二个是要检索的行数
mysql> select * from apps limit 1, 2;
+----+------------+-----------------------+---------+
| id | app_name | url | country |
+----+------------+-----------------------+---------+
| 2 | 微博 APP | http://weibo.com | CN |
| 3 | 淘宝 APP | http://www.taobao.com | CN |
+----+------------+-----------------------+---------+
2 rows in set (0.00 sec)
5.limit关键字和offset配合使用
limit可以配合offset使用, 如limit 2 offset 1(从行1开始后的2行,默认行数的角标为0)
mysql> select * from apps limit 2 offset 1;
+----+------------+-----------------------+---------+
| id | app_name | url | country |
+----+------------+-----------------------+---------+
| 2 | 微博 APP | http://weibo.com | CN |
| 3 | 淘宝 APP | http://www.taobao.com | CN |
+----+------------+-----------------------+---------+
2 rows in set (0.00 sec)