DML語句：
DML操作是指對數據庫中的表進行操作，主要包括記錄的插入（insert），更新（update），刪除（delete），查詢（select）。
記錄插入
創建表完成後就需要給器插入記錄和數據了，插入記錄基本語法如下：
INSERT tablename (fielde1,fielden2....)VALUES(value1,value2....);
下面我給我製作的表名爲class_1填入以下下信息
name分別爲liao，liaoxz，marry age爲18,18,28 sex 爲man,man,woman
mysql> insert class_1 (name,age,sex)values('liao','18','man');
Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> insert class_1 (name,age,sex)values('liaoxz','18','man');
Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> insert class_1 (name,age,sex)values('marry','28','woman');
Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> select name,age,sex from class_1 ;
+--------+------+------+
| name | age | sex |
+--------+------+------+
| marry | 28 | w |
| liaoxz | 18 | m |
| liao | 18 | m |
+--------+------+------+
3 rows in set (0.00 sec)注：可以不用指定字段名但是values後面的順序必須要和字段排序一樣，加入新的數據記錄時如果只指定其中幾個字段，其他默認爲null值
例如：
mysql> insert class_1 (name,age)values('tom','19');
Query OK, 1 row affected (0.00 sec)
mysql> select name,age,sex from class_1 ;
+--------+------+------+
| name | age | sex |
+--------+------+------+
| marry | 28 | w |
| liaoxz | 18 | m |
| liao | 18 | m |
| tom | 19 | NULL |
+--------+------+------+
4 rows in set (0.00 sec)
mysql> insert class_1 values('jarry','18','woman');
Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> select name,age,sex from class_1 ;
+--------+------+------+
| name | age | sex |
+--------+------+------+
| marry | 28 | w |
| liaoxz | 18 | m |
| liao | 18 | m |
| tom | 19 | NULL |
| jarry | 18 | w |
+--------+------+------+
5 rows in set (0.00 sec)同時加入多條記錄
mysql> insert class_1 values('wang','19','man'),('li','16','woman'),('liu','17','woman');
Query OK, 3 rows affected, 3 warnings (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 3
mysql> select name,age,sex from class_1 ;
+--------+------+------+
| name | age | sex |
+--------+------+------+
| marry | 28 | w |
| liaoxz | 18 | m |
| liao | 18 | m |
| tom | 19 | NULL |
| jarry | 18 | w |
| wang | 19 | m |
| li | 16 | w |
| liu | 17 | w |
+--------+------+------+
8 rows in set (0.00 sec)記錄更新
表中的值可以通過update來更新語法如下：
UPDATE tablename SET filed1=value1,filed2=value2...[WHERE CONDITION];
例 如將表中的liao 的age更改爲20：
mysql> update test.class_1 set age=20 where name="liao";Query OK, 0 rows affected (0.00 sec) Rows matched: 1 Changed: 0 Warnings: 0 mysql> select name,age from class_1; +--------+------+ | name | age | +--------+------+ | marry | 28 | | liaoxz | 18 | | liao | 20 | | tom | 19 | | jarry | 18 | | wang | 19 | | li | 16 | | liu | 17 | +--------+------+ 8 rows in set (0.00 sec)
記錄刪除
當數據不再需要時，可以使用delete將其刪除，例如將class_1中所有name爲liao的所有數據刪除；
語法如下：
DELETE FROM tablename [WHERE CONDITION];
mysql> delete from class_1 where name='liao'; Query OK, 1 row affected (0.00 sec) mysql> select name,age,sex from class_1; +--------+------+------+ | name | age | sex | +--------+------+------+ | marry | 28 | w | | liaoxz | 18 | m | | tom | 19 | NULL | | jarry | 18 | w | | wang | 19 | m | | li | 16 | w | | liu | 17 | w | +--------+------+------+ 7 rows in set (0.00 sec)
記錄查詢
當想要查看數據庫中其中一條數據信息時可以使用select命令查找；基本語法如下；
SELECT*FROM tablename [WHERE CONDITION];
常見用法
例1
查看錶中class_1中所有數據；
mysql> select * from test.class_1; +--------+------+------+ | name | age | sex | +--------+------+------+ | marry | 28 | w | | liaoxz | 18 | m | | tom | 19 | NULL | | jarry | 18 | w | | wang | 19 | m | | li | 16 | w | | liu | 17 | w | +--------+------+------+ 7 rows in set (0.00 sec)
例2
查看class_1中所有age爲19的用戶記錄
mysql> select * from class_1 where age=19; +------+------+------+ | name | age | sex | +------+------+------+ | tom | 19 | NULL | | wang | 19 | m | +------+------+------+ 2 rows in set (0.00 sec)
根據查詢不同要求可以將查詢分爲以下幾類：
1）去重查詢
使用distinct關鍵字來實現
例如查看錶class_2中age去重後顯示出來
mysql> select distinct age from class_2; +------+ | age | +------+ | 18 | | 19 | | 16 | +------+ 3 rows in set (0.00 sec)
從上面可以看出class_2表中學生age都在16,18,19之間
2）條件查詢
條件查詢同where後的字段進行條件比較，比較符號包括 >,<,=,<=,>=,!= 還可以使用多個條件 使用or ，and等邏輯運算符進行多條件查詢。
例子1 查看class_1表中age大於等於18的數據，
mysql> select name,age,sex from class_1 where age>=18; +--------+------+------+ | name | age | sex | +--------+------+------+ | marry | 28 | w | | liaoxz | 18 | m | | tom | 19 | NULL | | jarry | 18 | w | | wang | 19 | m | +--------+------+------+ 5 rows in set (0.00 sec)
例子2 查看class_1表中sex爲man，且年齡大於等於18的數據
mysql> select name,age,sex from class_1 where sex='m' and age>=18; +--------+------+------+ | name | age | sex | +--------+------+------+ | liaoxz | 18 | m | | wang | 19 | m | +--------+------+------+ 2 rows in set (0.00 sec)
3）輸出排序查詢
在查詢過程中常會將數據進行排序後進行查看，在這裏排序查看使用關鍵字 ORDER BY來實現，語法如下：
SELECT * FROM tablename [WHERE CONDITION] [ORDER BY filed1 [DESC|ASC]];
DESC是按照字段進行排序，如果第一個字段值一樣賦值會按照第二個字段進行比較排序，ASC是按照升序排列，不加sac默認也是升序排列
例子 1 將表class_1按照age進行排序，
mysql> select name,age,sex from class_1 order by age asc; +--------+------+-------+ | name | age | sex | +--------+------+-------+ | li | 16 | woman | | liu | 17 | woman | | liaoxz | 18 | man | | jarry | 18 | woman | | tom | 19 | NULL | | wang | 19 | man | | marry | 28 | woman | +--------+------+-------+ 7 rows in set (0.00 sec)
4）限定輸出查詢
當一張表中數據過多時，我們只想查看其中一部分可以使用LIMIT關鍵字實現，LIMIT 語法如下：
SELECT ... [LIMIT offset_start,row_count]
offset_start表示記錄起始偏移量，row_count表示行數；
注意：默認其實偏移量爲0，例；顯示class_1表中按照age排序後的前三條記錄
mysql> select * from class_1 order by age; +--------+------+-------+ | name | age | sex | +--------+------+-------+ | li | 16 | woman | | liu | 17 | woman | | liaoxz | 18 | man | | jarry | 18 | woman | | tom | 19 | NULL | | wang | 19 | man | | marry | 28 | woman | +--------+------+-------+ 7 rows in set (0.00 sec) mysql> select * from class_1 order by age limit 3; +--------+------+-------+ | name | age | sex | +--------+------+-------+ | li | 16 | woman | | liu | 17 | woman | | liaoxz | 18 | man | +--------+------+-------+ 3 rows in set (0.00 sec)
例2 顯示從第3條開始後的三條記錄
mysql> select * from class_1 order by age limit 2,3; +--------+------+-------+ | name | age | sex | +--------+------+-------+ | liaoxz | 18 | man | | jarry | 18 | woman | | tom | 19 | NULL | +--------+------+-------+ 3 rows in set (0.00 sec)
寫在後面：多表操作將在後續文章中陸續貼出