重拾SQL——表中索值
2024-08-23 13:43:17
2016.10.23 + 2016.11.02
1.选择所有数据（查看整表）
MariaDB [tianyuan]> select * from pet;
+----------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+----------+--------+---------+------+------------+-------+
| Fluffy | Harold | cat | f | 1993-02-04 | NULL |
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
| Puffball | Diane | hamster | f | 1999-03-30 | NULL |
+----------+--------+---------+------+------------+-------+
4 rows in set (0.00 sec)
2.修改数据的二种办法
2.1 直接单处更新（优）
MariaDB [tianyuan]> UPDATE pet SET birth = '1994-04-12' WHERE name = 'Buffy';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [tianyuan]> select * from pet;
+----------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+----------+--------+---------+------+------------+-------+
| Fluffy | Harold | cat | f | 1993-02-04 | NULL |
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1994-04-12 | NULL |
| Puffball | Diane | hamster | f | 1999-03-30 | NULL |
+----------+--------+---------+------+------------+-------+
4 rows in set (0.00 sec)
2.2 整表删除，重新加载
编辑文件"1.txt"改正错误，然后使用DELETE和LOAD DATA清空并重新装载表:
MariaDB [tianyuan]> DELETE FROM pet;
MariaDB [tianyuan]> LOAD DATA LOCAL INFILE 'pet.txt' INTO TABLE pet;
效果和上面一样，然而, 如果这样操做，必须重新输入Puffball记录。
2.选择特殊行
2.1 选择行
MariaDB [tianyuan]> select * from pet where name='Buffy';
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Buffy | Harold | dog | f | 1994-04-12 | NULL |
+-------+--------+---------+------+------------+-------+
1 row in set (0.00 sec)
2.2 活用WHERE
WHERE... : 指定条件（=, >, <）
MariaDB [tianyuan]> SELECT * FROM pet WHERE birth > '1994-4-12';
+-------+-------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+-------+---------+------+------------+-------+
| yuner | ayuan | person | f | 1997-11-13 | NULL |
+-------+-------+---------+------+------------+-------+
1 row in set (0.00 sec)
2.3 WHERE...AND... : 组合条件
MariaDB [tianyuan]> SELECT * FROM pet WHERE species = 'dog' AND sex = 'f';
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+
1 row in set (0.00 sec)
2.4 WHERE...OR... : 组合条件
SELECT * FROM pet WHERE species = 'dog' OR species = 'cat';
+--------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+--------+--------+---------+------+------------+-------+
| Fluffy | Harold | cat | f | 1993-02-04 | NULL |
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+--------+--------+---------+------+------------+-------+
3 rows in set (0.00 sec)
2.5 WHERE...AND...OR... : 组合条件
AND和OR可以混用，但AND比OR具有更高的优先级。如果你使用两个操作符，使用圆括号指明如何对条件进行分组是一个好主意。
MariaDB [tianyuan]> SELECT * FROM pet WHERE (species = 'cat' AND sex = 'm')
-> OR (species = 'dog' AND sex = 'f');
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+
2 rows in set (0.00 sec)
3.选择特殊列
3.1 宠物的名字与出生日期列组合呈现
MariaDB [tianyuan]> SELECT name, birth FROM pet;
+--------+------------+
| name | birth |
+--------+------------+
| Fluffy | 1993-02-04 |
| Claws | 1994-03-17 |
| Buffy | 1989-05-13 |
| yuner | 1997-11-13 |
+--------+------------+
4 rows in set (0.00 sec)
3.2 宠物的主人名单列呈现
MariaDB [tianyuan]> SELECT owner FROM pet;
+--------+
| owner |
+--------+
| Harold |
| Gwen |
| Harold |
| ayuan |
+--------+
4 rows in set (0.00 sec)
3.3 Distinct: 上条名单去重效果
MariaDB [tianyuan]> SELECT DISTINCT owner FROM pet;
+--------+
| owner |
+--------+
| Harold |
| Gwen |
| ayuan |
+--------+
3 rows in set (0.00 sec)
3.4 WHERE子句结合行选择与列选择
MariaDB [tianyuan]> SELECT name, species, birth FROM pet
-> WHERE species = 'dog' OR species = 'cat';
+--------+---------+------------+
| name | species | birth |
+--------+---------+------------+
| Fluffy | cat | 1993-02-04 |
| Claws | cat | 1994-03-17 |
| Buffy | dog | 1989-05-13 |
+--------+---------+------------+
3 rows in set (0.00 sec)
4.分类行
4.1 排序（ORDER BY）
MariaDB [tianyuan]> SELECT name, birth FROM pet ORDER BY birth;
+--------+------------+
| name | birth |
+--------+------------+
| Buffy | 1989-05-13 |
| Fluffy | 1993-02-04 |
| Claws | 1994-03-17 |
| yuner | 1997-11-13 |
+--------+------------+
4 rows in set (0.06 sec)
4.2 降序（DESC）
MariaDB [tianyuan]> SELECT name, birth FROM pet ORDER BY birth DESC;
+--------+------------+
| name | birth |
+--------+------------+
| yuner | 1997-11-13 |
| Claws | 1994-03-17 |
| Fluffy | 1993-02-04 |
| Buffy | 1989-05-13 |
+--------+------------+
4 rows in set (0.00 sec)
4.3 混合序
species升，birth降
MariaDB [tianyuan]> select name, species, birth FROM pet
-> ORDER BY species, birth DESC;
+--------+---------+------------+
| name | species | birth |
+--------+---------+------------+
| Claws | cat | 1994-03-17 |
| Fluffy | cat | 1993-02-04 |
| Buffy | dog | 1989-05-13 |
| yuner | person | 1997-11-13 |
+--------+---------+------------+
4 rows in set (0.06 sec)
species降，birth降
MariaDB [tianyuan]> select name, species, birth FROM pet
-> ORDER BY species DESC, birth DESC;
+--------+---------+------------+
| name | species | birth |
+--------+---------+------------+
| yuner | person | 1997-11-13 |
| Buffy | dog | 1989-05-13 |
| Claws | cat | 1994-03-17 |
| Fluffy | cat | 1993-02-04 |
+--------+---------+------------+
4 rows in set (0.00 sec)
5.日期计算
5.1 宠物年龄计算（简单的日期计算）
MariaDB [tianyuan]> SELECT name, birth, CURDATE(),
-> (YEAR(CURDATE())-YEAR(birth))
-> - (RIGHT(CURDATE(),5)<RIGHT(birth,5))
-> AS age
-> FROM pet;
+--------+---------+------------+
| name | species | birth |
+--------+---------+------------+
| yuner | person | 1997-11-13 |
| Buffy | dog | 1989-05-13 |
| Claws | cat | 1994-03-17 |
| Fluffy | cat | 1993-02-04 |
+--------+---------+------------+
4 rows in set (0.00 sec)
- CURDATE()：提前当前精确日期
- YEAR()：提取日期的年部分
- RIGHT()：提取日期的MM-DD (日历年)部分的最右面5个字符（即月与日）。
- 比较MM-DD值的表达式部分的值一般为1或0，如果CURDATE()（今年）的月与日比birth（出生时）的月与日早，则年份应减去1（因为还没到达生日日期）。
5.2 已死亡宠物年龄计算（带条件的日期计算）
MariaDB [tianyuan]> select name, birth, death,
-> (YEAR(death)-YEAR(birth)) - (Right(death,5)<RIGHT(birth,5))
-> AS age
-> FROM pet WHERE death IS NOT NULL ORDER BY age;
+--------+------------+------------+------+
| name | birth | death | age |
+--------+------------+------------+------+
| Fluffy | 1993-02-04 | 1995-02-04 | 2 |
+--------+------------+------------+------+
1 row in set (0.03 sec)
5.3 哪个宠物下个月过生日
MariaDB [tianyuan]> SELECT name, birth FROM pet WHERE MONTH(birth) = 11;
+-------+------------+
| name | birth |
+-------+------------+
| yuner | 1997-11-13 |
+-------+------------+
1 row in set (0.00 sec)
5.3.1 疑问：11能不能换成本月＋1？或者取余
MariaDB [tianyuan]> SELECT name, birth FROM pet WHERE MONTH(birth) = (MONTH(birth)+1);
Empty set (0.00 sec)
MariaDB [tianyuan]> SELECT name, birth FROM pet WHERE MONTH(birth) = (MONTH(birth)+MONTH(birth)/MONTH(birth));
Empty set (0.07 sec)
5.3.2 正解1
MariaDB [tianyuan]> SELECT name, birth FROM pet
-> WHERE MONTH(birth) = MONTH(DATE_ADD(CURDATE(),INTERVAL 1 MONTH));
DATE_ADD( )允许在一个给定的日期上加上时间间隔
5.3.3 正解2
MariaDB [tianyuan]> SELECT name, birth FROM pet
-> WHERE MONTH(birth) = MOD(MONTH(CURDATE()), 12) + 1;
得到的结果是一致的，因为目的一样。
+-------+------------+
| name | birth |
+-------+------------+
| yuner | 1997-11-13 |
+-------+------------+
1 row in set (0.11 sec)
6.NULL值操作
6.1 算术比较操作符无效
MariaDB [tianyuan]> SELECT 1 = NULL, 1 <> NULL, 1 < NULL, 1 > NULL;
+----------+-----------+----------+----------+
| 1 = NULL | 1 NULL | 1 NULL |
+----------+-----------+----------+----------+
| NULL | NULL | NULL | NULL |
+----------+-----------+----------+----------+
1 row in set (0.00 sec)
6.2 IS NULL, IS NOT NULL
MariaDB [tianyuan]> SELECT 1 IS NULL, 1 IS NOT NULL, null IS NULL, null IS NOT NULL;
+-----------+---------------+--------------+------------------+
| 1 IS NULL | 1 IS NOT NULL | null IS NULL | null IS NOT NULL |
+-----------+---------------+--------------+------------------+
| 0 | 1 | 1 | 0 |
+-----------+---------------+--------------+------------------+
1 row in set (0.00 sec)
7.模式匹配
7.1 x％：以x开头的字符串
MariaDB [tianyuan]> SELECT * FROM pet WHERE name LIKE 'y%';
+-------+-------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+-------+---------+------+------------+-------+
| yuner | ayuan | person | f | 1997-11-13 | NULL |
+-------+-------+---------+------+------------+-------+
1 row in set (0.00 sec)
7.2 ％x：以x结尾的字符串
MariaDB [tianyuan]> SELECT * FROM pet WHERE name LIKE '%r';
+-------+-------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+-------+---------+------+------------+-------+
| yuner | ayuan | person | f | 1997-11-13 | NULL |
+-------+-------+---------+------+------------+-------+
1 row in set (0.00 sec)
7.3 ％x%：包含x的字符串
MariaDB [tianyuan]> SELECT * FROM pet WHERE name LIKE '%un%';
+-------+-------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+-------+---------+------+------------+-------+
| yuner | ayuan | person | f | 1997-11-13 | NULL |
+-------+-------+---------+------+------------+-------+
1 row in set (0.00 sec)
7.4 x：正好包含x个字符的字符串
MariaDB [tianyuan]> SELECT * FROM pet WHERE name LIKE '______';（6个下划线）
+--------+--------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+--------+--------+---------+------+------------+------------+
| Fluffy | Harold | cat | f | 1993-02-04 | 1995-02-04 |
+--------+--------+---------+------+------------+------------+
1 row in set (0.00 sec)
7.5 MySQL正则表达式
操作中遇到了问题，暂时跳过，语法较为简单，只是需要练习。
MariaDB [tianyuan]> SELECT * FROM pet WHERE name REGEXP '^.{5}$';
ERROR 1139 (42000): Got error 'this version of PCRE is compiled
without UTF support at offset 0' from regexp
8.计数行
8.1 在pet表中有多少行?(动物数目)
MariaDB [tianyuan]> SELECT COUNT(*) FROM pet;
+----------+
| COUNT(*) |
+----------+
| 4 |
+----------+
1 row in set (0.00 sec)
8.2 每个主人有多少宠物(GROUP BY)
MariaDB [tianyuan]> SELECT owner, COUNT(*) FROM pet GROUP BY owner;
+--------+----------+
| owner | COUNT(*) |
+--------+----------+
| ayuan | 1 |
| Gwen | 1 |
| Harold | 2 |
+--------+----------+
3 rows in set (0.00 sec)
8.3 每种动物的数量?
MariaDB [tianyuan]> SELECT species, COUNT(*) FROM pet GROUP BY owner;
+---------+----------+
| species | COUNT(*) |
+---------+----------+
| person | 1 |
| cat | 1 |
| cat | 2 |
+---------+----------+
3 rows in set (0.00 sec)
8.4 按种类和性别组合的动物数量
MariaDB [tianyuan]> SELECT species, sex, COUNT(*) FROM pet GROUP BY species, sex;
+---------+------+----------+
| species | sex | COUNT(*) |
+---------+------+----------+
| cat | f | 1 |
| cat | m | 1 |
| dog | f | 1 |
| person | f | 1 |
+---------+------+----------+
4 rows in set (0.00 sec)
8.5 只对狗和猫进行检索时
MariaDB [tianyuan]> SELECT species, sex, COUNT(*) FROM pet
-> WHERE species = 'dog' OR species = 'cat'
-> GROUP BY species, sex;
+---------+------+----------+
| species | sex | COUNT(*) |
+---------+------+----------+
| cat | f | 1 |
| cat | m | 1 |
| dog | f | 1 |
+---------+------+----------+
3 rows in set (0.00 sec)
8.6 已知性别的按性别的动物数目
MariaDB [tianyuan]> SELECT species, sex, COUNT(*) FROM pet -> WHERE sex IS NOT NULL
-> GROUP BY species, sex;
+---------+------+----------+
| species | sex | COUNT(*) |
+---------+------+----------+
| cat | f | 1 |
| cat | m | 1 |
| dog | f | 1 |
| person | f | 1 |
+---------+------+----------+
4 rows in set (0.00 sec)
9.使用1个以上的表
9.1 创建第二张表
MariaDB [tianyuan]> CREATE TABLE event (name VARCHAR(20), date DATE,
-> type VARCHAR(15), remark VARCHAR(255));
Query OK, 0 rows affected (0.10 sec)
9.2 装载event.txt文件
LOAD DATA LOCAL INFILE 'desktop/event.txt' INTO TABLE event;
MariaDB [tianyuan]> select * from event;
+--------+------------+--------+-----------------------------+
| name | date | type | remark |
+--------+------------+--------+-----------------------------+
| Fluffy | 1995-05-15 | litter | 4 kittens, 3 female, 1 male |
| Buffy | 1993-06-23 | litter | 5 puppies, 2 female, 3 male |
| Buffy | 1994-06-19 | litter | 3 puppies, 3 female |
| Chirpy | 1999-03-21 | vet | needed beak straightened |
| Slim | 1997-08-03 | vet | broken rib |
| Bowser | 1991-10-10 | kennel | NULL |
+--------+------------+--------+-----------------------------+
7 rows in set (0.00 sec)
9.3 根据需要来使用两张表的数据（组成新表呈现）
MariaDB [tianyuan]> SELECT pet.name,
-> (YEAR(date)-YEAR(birth)) - (RIGHT(date,5)<RIGHT(birth,5)) AS age,
-> remark
-> FROM pet, event
-> WHERE pet.name = event.name AND event.type = 'litter';
+--------+------+-----------------------------+
| name | age | remark |
+--------+------+-----------------------------+
| Fluffy | 2 | 4 kittens, 3 female, 1 male |
| Buffy | -24 | 5 puppies, 2 female, 3 male |
| Buffy | -23 | 3 puppies, 3 female |
+--------+------+-----------------------------+
3 rows in set (0.00 sec)
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