系列文章：
数据库SQL语言入门（一）
数据库SQL语言入门（二）
DML语句
DML操作指对数据中的表记录的操作，主要包括常用的增(insert)、删(delete)、改(update)、查(select)。
1 增: insert 插入记录
INSERT INTO tablename
(field1,field2,......fieldn)
VALUES(value1,value2,......valuesn);
方法1:
mysql> insert into table1 (level_update, level_guid, level_name) values('2018-10-19', '1000', '青铜')
-> ;
Query OK, 1 row affected (0.01 sec)
mysql> select * from table1
-> ;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
+--------------+------------+------------+
1 row in set (0.00 sec)
方法2:可以不指定字段名直接插入，但values中的顺序需要和数据库中字段名顺序相同。
mysql> insert into table1 values('2018-10-19', '1001', '白银');
Query OK, 1 row affected (0.00 sec)
mysql> select * from table1
-> ;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
+--------------+------------+------------+
2 rows in set (0.00 sec)
- 含可空字段 若不填，默认NULL。
- 非空但含有默认值 若不填，默认值。
- 自增字段 若不填，自增的下一个数字
这三种字段，可以不用在insert后的字段列表出现，values后面只需添加前面出现的字段对应的value。
mysql> desc table1;
+--------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+-------------+------+-----+---------+-------+
| level_update | date | YES | | NULL | |
| level_guid | int(5) | YES | | NULL | |
| level_name | varchar(10) | YES | | NULL | |
+--------------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
mysql> insert into table1 (level_guid, level_name) values('1002', '黄金');
Query OK, 1 row affected (0.00 sec)
mysql> select * from table1;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
| NULL | 1002 | 黄金 |
+--------------+------------+------------+
3 rows in set (0.00 sec)
MySQL 还支持一次性插入多条记录。这个特性使得MySQL在插入大量数据时，可以节省很多的网络开销，大大提高插入效率。
INSERT INTO tablename (field1, field2,......fieldn) VALUES
(record1_value1, record1_value2,......record1_valuesn),
(record2_value1, record2_value2,......record2_valuesn),
......
(recordn_value1, recordn_value2,......recordn_valuesn) ;
如: 一次插入 3 条数据
mysql> insert into table1 (level_update, level_guid, level_name) value('2018-10-19', '1003', '铂金'),
-> ('2018-10-19', '1004', '钻石'),
-> ('2018-10-19', '1005', '星耀');
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select * from table1;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
| NULL | 1002 | 黄金 |
| 2018-10-19 | 1003 | 铂金 |
| 2018-10-19 | 1004 | 钻石 |
| 2018-10-19 | 1005 | 星耀 |
+--------------+------------+------------+
6 rows in set (0.00 sec)
2.1 更新记录(一条) update
UPDATE tablename SET field1=value1，field2.=value2，......fieldn=valuen [WHERE CONDITION]
将表 table1 中的 level_guid 为 “1002” 这行的 level_update 的值从 “NULL” 改为 “2018-10-19”。
mysql> update table1 set level_update='2018-10-19' where level_guid='1002';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from table1;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-19 | 1003 | 铂金 |
| 2018-10-19 | 1004 | 钻石 |
| 2018-10-19 | 1005 | 星耀 |
+--------------+------------+------------+
6 rows in set (0.00 sec)
2.2 更新记录(多条) update
MySQL支持使用 update 命令同时更新多个表的多个字段的数据。语法:
UPDATE t1,t2...tn set t1.field1=expr1,tn.fieldn=exprn [WHERE CONDITION]
先创建表 table2
mysql> create table table2;
ERROR 1113 (42000): A table must have at least 1 column
mysql> create table table2 (level_guid int(5), level_name varchar(6), level_update date);
Query OK, 0 rows affected (0.02 sec)
mysql> desc table2;
+--------------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+------------+------+-----+---------+-------+
| level_guid | int(5) | YES | | NULL | |
| level_name | varchar(6) | YES | | NULL | |
| level_update | date | YES | | NULL | |
+--------------+------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
mysql> select * from table2
Empty set (0.00 sec)
mysql> insert into table2 values('1004', '钻石', '2018-10-19');
Query OK, 1 row affected (0.00 sec)
mysql> select * from table2;
+------------+------------+--------------+
| level_guid | level_name | level_update |
+------------+------------+--------------+
| 1004 | 钻石 | 2018-10-19 |
+------------+------------+--------------+
1 row in set (0.00 sec)
执行:如果表 table1 和表 table2 的 level_guid 有相同的，那么，表 table1 的 level_update 的value更新为“2018-10-20”，表 table2 的 level_update 的value更新为“2018-10-21”。
//执行多条数据记录更新
mysql> update table1 a,table2 b set a.level_update='2018-10-20',b.level_update='2018-10-21' where a.level_guid=b.level_guid;
Query OK, 2 rows affected (0.01 sec)
Rows matched: 2 Changed: 2 Warnings: 0
ysql> select * from table1;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-19 | 1003 | 铂金 |
| 2018-10-20 | 1004 | 钻石 |
| 2018-10-19 | 1005 | 星耀 |
+--------------+------------+------------+
6 rows in set (0.00 sec)
mysql> select * from table2;
+------------+------------+--------------+
| level_guid | level_name | level_update |
+------------+------------+--------------+
| 1004 | 钻石 | 2018-10-21 |
+------------+------------+--------------+
1 row in set (0.00 sec)
从结果上看，两个表的数据都更新了。
注意: 多表更新的语法更多的用在了根据一个表的字段，来动态的更新另一个表的字段。
3.1 删除记录(单表中的) delete
DELETE FROM tablename [WHERE CONDITION]
如: 将表 table1 中的level_guid为1005的那一行删去。
mysql> delete from table1 where level_guid='1005';
Query OK, 1 row affected (0.00 sec)
mysql> select * from table1;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-19 | 1003 | 铂金 |
| 2018-10-20 | 1004 | 钻石 |
+--------------+------------+------------+
5 rows in set (0.00 sec)
3.2 删除记录(多表中的) delete
MySQL中除了支持一次性更新多表中的数据，还可以一次性删除多个表中的数据记录。
DELETE t1,t2...tn FROM t1,t2...tn [WHERE CONDITION]
如：删除表 table1 和表 table2 中level_guid相等的行。
mysql> delete a,b from table1 a,table2 b where a.level_guid=b.level_guid;
Query OK, 2 rows affected (0.00 sec)
mysql> select * from table1;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-19 | 1003 | 铂金 |
+--------------+------------+------------+
4 rows in set (0.00 sec)
mysql> select * from table2;
Empty set (0.00 sec)
注意:不管是单表还是多表，不加 where 条件将会把表的所有记录删除，所以操作时一定要小心。
4 查询记录 select
SELECT * FROM tablename [WHERE CONDITION]
“ * ”表示选出表中所有的数据记录，等同于用“ , ”号分割的所有字段的写法:
mysql> select * from table1;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-19 | 1003 | 铂金 |
+--------------+------------+------------+
4 rows in set (0.00 sec)
mysql> select level_update, level_guid, level_name from table1;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-19 | 1003 | 铂金 |
+--------------+------------+------------+
4 rows in set (0.00 sec)
在实际应用中常常遇到的查询情况:
- 查询不重复的记录 distinct+字段
mysql> select distinct level_update from table1;
+--------------+
| level_update |
+--------------+
| 2018-10-19 |
+--------------+
1 row in set (0.00 sec)
- 条件查询
mysql> select * from table1 where level_name='黄金';
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1002 | 黄金 |
+--------------+------------+------------+
1 row in set (0.00 sec)
where + 条件: 其中，
条件中除了“ = ”，还可以使用 >、 <、>=、<=、!=等比较运算符；
多个条件时，之间也可以使用or、and等逻辑运算符，进行多条件联合查询。
mysql> select * from table1 where level_guid>'1001' or level_name='青铜';
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-19 | 1003 | 铂金 |
+--------------+------------+------------+
3 rows in set (0.00 sec)
- 排除和限制
语法：
SELECT * FROM tablename [WHERE CONDITION] [ORDER BY field1 [DESC|ASC] ， field2 [DESC|ASC]，......fieldn [DESC|ASC]]
实例:
mysql> select * from table1;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-19 | 1003 | 铂金 |
| 2018-10-22 | 1001 | 钻石 |
| 2018-10-22 | 1002 | 星耀 |
+--------------+------------+------------+
6 rows in set (0.00 sec)
//level_guid的正序排列输出：从低到高
mysql> select * from table1 order by level_guid;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
| 2018-10-22 | 1001 | 钻石 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-22 | 1002 | 星耀 |
| 2018-10-19 | 1003 | 铂金 |
+--------------+------------+------------+
6 rows in set (0.00 sec)
//level_guid的倒叙排列输出：从高到低
mysql> select * from table1 order by level_guid desc;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1003 | 铂金 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-22 | 1002 | 星耀 |
| 2018-10-19 | 1001 | 白银 |
| 2018-10-22 | 1001 | 钻石 |
| 2018-10-19 | 1000 | 青铜 |
+--------------+------------+------------+
6 rows in set (0.00 sec)
//多字段(A,B,C...)正序排列，如果A相同，按B正序排列；如果B相同，按C正序排列；...
mysql> select * from table1 order by level_guid,level_update;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
| 2018-10-22 | 1001 | 钻石 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-22 | 1002 | 星耀 |
| 2018-10-19 | 1003 | 铂金 |
+--------------+------------+------------+
6 rows in set (0.00 sec)
//多字段(A,B,C...)倒序排列，如果A相同，按B倒序排列；如果B相同，按C倒序排列；...
mysql> select * from table1 order by level_guid,level_update desc;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-22 | 1001 | 钻石 |
| 2018-10-19 | 1001 | 白银 |
| 2018-10-22 | 1002 | 星耀 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-19 | 1003 | 铂金 |
+--------------+------------+------------+
6 rows in set (0.00 sec)
limit: 可以让排序后的记录，只显示其中的一部分。
SELECT ......[LIMIT offset_start,row_count]
如:
mysql> select * from table1 order by level_guid limit 4;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-19 | 1000 | 青铜 |
| 2018-10-19 | 1001 | 白银 |
| 2018-10-22 | 1001 | 钻石 |
| 2018-10-19 | 1002 | 黄金 |
+--------------+------------+------------+
4 rows in set (0.00 sec)
mysql> select * from table1 order by level_guid limit 2,4;
+--------------+------------+------------+
| level_update | level_guid | level_name |
+--------------+------------+------------+
| 2018-10-22 | 1001 | 钻石 |
| 2018-10-19 | 1002 | 黄金 |
| 2018-10-22 | 1002 | 星耀 |
| 2018-10-19 | 1003 | 铂金 |
+--------------+------------+------------+
4 rows in set (0.00 sec)
limit 经常和 order by 一起配合使用来进行记录的分页显示。
注意: limit 属于 MySQL 扩展 SQL92 后的语法，在其他数据库上并不能通用。
- 聚合
语法
SELECT [field1,field2,......fieldn] fun_name FROM tablename
[WHERE where_contition]
[GROUP BY field1,field2,......fieldn
[WITH ROLLUP]]
[HAVING where_contition]
参考:
《深入浅出MySQL》