數值類型
tinyint 1bytes
smallint 2bytes
mediumint 3bytes
int|intergint 4bytes
bigint 8bytes
float 4bytes 單精度
double 8bytes 雙精度
示例1： int數據類型 （int寬度並不能限制）
create table test(id int(4));
insert test VALUES(11111111);
select * from test;
alter table test change a a int(5);
#創建表一個是默認寬度的int，一個是指定寬度的int(5) mysql> create table t1 (id1 int,id2 int(5)); Query OK, 0 rows affected (0.02 sec)
#像t1中插入數據1，1 mysql> insert into t1 values (1,1); Query OK, 1 row affected (0.01 sec)
#可以看出結果上並沒有異常 mysql> select * from t1;
+‐‐‐‐‐‐+‐‐‐‐‐‐+
| id1 | id2 |
+‐‐‐‐‐‐+‐‐‐‐‐‐+
| 1 | 1 |
+‐‐‐‐‐‐+‐‐‐‐‐‐+
row in set (0.00 sec)
#那麼當我們插入了比寬度更大的值，會不會發生報錯呢？ mysql> insert into t1 values (111111,111111); Query OK, 1 row affected (0.00 sec)
#答案是否定的，id2仍然顯示了正確的數值，沒有受到寬度限制的影響
mysql> select * from t1;
+‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐+
| id1 | id2 |
+‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐+
| 0000000001 | 00001 |
| 0000111111 | 111111 |
+‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐+
rows in set (0.00 sec)
示例2：小數示例類型; 小數位會被限制，並且遵循四捨五入
#創建表的三個字段分別爲float，double和decimal參數表示一共顯示5位，小數部分佔2位 mysql> create table t2 (id1 float(5,2),id2 double(5,2),id3 decimal(5,2)); Query OK, 0 rows affected (0.02 sec)
#向表中插入1.23，結果正常 mysql> insert into t2 values (1.23,1.23,1.23); Query OK, 1 row affected (0.00 sec)
mysql> select * from t2;
+‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐+
| id1 | id2 | id3 |
+‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐+
| 1.23 | 1.23 | 1.23 |
+‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐+
row in set (0.00 sec)
#向表中插入1.234，會發現4都被截斷了 mysql> insert into t2 values (1.234,1.234,1.234); Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> select * from t2;
+‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐+
| id1 | id2 | id3 |
+‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐+
| 1.23 | 1.23 | 1.23 |
| 1.23 | 1.23 | 1.23 |
+‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐+
rows in set (0.00 sec)
#向表中插入1.235發現數據雖然被截斷，但是遵循了四捨五入的規則 mysql> insert into t2 values (1.235,1.235,1.235); Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> select * from t2;
+‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐+
| id1 | id2 | id3 |
+‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐+
| 1.23 | 1.23 | 1.23 |
| 1.23 | 1.23 | 1.23 |
| 1.24 | 1.24 | 1.24 |
+‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐‐+
rows in set (0.00 sec)
實例3：時間數據類型
mysql> create table t4 (d date,t time,dt datetime);
Query OK, 0 rows affected (0.02 sec)
mysql> desc t4;
+‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+
| Field | Type | Null | Key | Default | Extra |
+‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+
| d | date | YES | | NULL | |
| t | time | YES | | NULL | |
| dt | datetime | YES | | NULL | |
+‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐+‐‐‐‐‐+‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐+
rows in set (0.01 sec)
mysql> insert into t4 values (now(),now(),now());
Query OK, 1 row affected, 1 warning (0.01 sec)
mysql> select * from t4;
+‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+
| d | t | dt |
+‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+
| 2018‐09‐21 | 14:51:51 | 2018‐09‐21 14:51:51 |
+‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+
row in set (0.00 sec)
mysql> insert into t4 values (null,null,null);
Query OK, 1 row affected (0.01 sec)
mysql> select * from t4;
+‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+
| d | t | dt |
+‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+
| 2018‐09‐21 | 14:51:51 | 2018‐09‐21 14:51:51 |
| NULL | NULL | NULL |
+‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+
rows in set (0.00 sec)
當插入NULL值時，TIMESTAMP數據類型會將當前數據插入
示例4：字符串數據類型：超過指定寬度的字符串內容會被截取
varchar數據類型在定義寬度的時候：不管字符串長度爲多少，總是分配寬度值所對應的長度。
char數據類型在定義寬度的時候；字符串存儲長度爲多少，就分配多長的空間。
mysql> create table t9 (v varchar(4),c char(4));
Query OK, 0 rows affected (0.01 sec)
mysql> insert into t9 values ('ab ','ab ');
Query OK, 1 row affected (0.00 sec)
# 在檢索的時候char數據類型會去掉空格
mysql> select * from t9;
+‐‐‐‐‐‐+‐‐‐‐‐‐+
| v | c |
+‐‐‐‐‐‐+‐‐‐‐‐‐+
| ab | ab |
+‐‐‐‐‐‐+‐‐‐‐‐‐+
row in set (0.00 sec)
# 來看看對查詢結果計算的長度
mysql> select length(v),length(c) from t9;
+‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐+
| length(v) | length(c) |
+‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐+
| 4 | 2 |
+‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐+
row in set (0.00 sec)
# 當存儲的長度超出定義的長度，會截斷
mysql> insert into t9 values ('abcd ','abcd ');
Query OK, 1 row affected, 1 warning (0.01 sec)
mysql> select * from t9;
+‐‐‐‐‐‐+‐‐‐‐‐‐+
| v | c |
+‐‐‐‐‐‐+‐‐‐‐‐‐+
| ab | ab |
| abcd | abcd |
+‐‐‐‐‐‐+‐‐‐‐‐‐+
rows in set (0.00 sec)
示例5：set數據類型和enum數據類型
mysql> create table t10 (name char(20),gender enum('female','male'));
Query OK, 0 rows affected (0.01 sec)
# 選擇enum('female','male')中的一項作爲gender的值，可以正常插入
mysql> insert into t10 values ('nezha','male');
Query OK, 1 row affected (0.00 sec)
# 不能同時插入'male,female'兩個值，也不能插入不屬於'male,female'的值
mysql> insert into t10 values ('nezha','male,female');
ERROR 1265 (01000): Data truncated for column 'gender' at row 1
mysql> create table t11 (name char(20),hobby set('抽菸','喝酒','燙頭','翻車'));
Query OK, 0 rows affected (0.01 sec)
# 可以任意選擇set('抽菸','喝酒','燙頭','翻車')中的項，並自帶去重功能
mysql> insert into t11 values ('yuan','燙頭,喝酒,燙頭');
Query OK, 1 row affected (0.01 sec)
mysql> select * from t11;
+‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+
| name | hobby |
+‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+
| yuan | 喝酒,燙頭 |
+‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+
row in set (0.00 sec)
# 不能選擇不屬於set('抽菸','喝酒','燙頭','翻車')中的項，
mysql> insert into t11 values ('alex','燙頭,翻車,看妹子');
ERROR 1265 (01000): Data truncated for column 'hobby' at row 1