Numeric types
1, integer type
Integer type: TINYINT SMALLINT MEDIUMINT INT BIGINT
Role: store age, grade, id, number, etc. of various
========================================
tinyint[(m)] [unsigned] [zerofill]
小整数，数据类型用于保存一些范围的整数数值范围：
有符号：
-128 ～ 127
无符号：
0 ～ 255
PS： MySQL中无布尔值，使用tinyint(1)构造。
========================================
int[(m)][unsigned][zerofill]
整数，数据类型用于保存一些范围的整数数值范围：
有符号：
-2147483648 ～ 2147483647
无符号：
0 ～ 4294967295
========================================
bigint[(m)][unsigned][zerofill]
大整数，数据类型用于保存一些范围的整数数值范围：
有符号：
-9223372036854775808 ～ 9223372036854775807
无符号：
0 ～ 18446744073709551615verification
=========有符号和无符号tinyint==========
#tinyint默认为有符号
MariaDB [db1]> create table t1(x tinyint); #默认为有符号，即数字前有正负号
MariaDB [db1]> desc t1;
MariaDB [db1]> insert into t1 values
-> (-129),
-> (-128),
-> (127),
-> (128);
MariaDB [db1]> select * from t1;
+------+
| x |
+------+
| -128 | #-129存成了-128
| -128 | #有符号，最小值为-128
| 127 | #有符号，最大值127
| 127 | #128存成了127
+------+
#设置无符号tinyint
MariaDB [db1]> create table t2(x tinyint unsigned);
MariaDB [db1]> insert into t2 values
-> (-1),
-> (0),
-> (255),
-> (256);
MariaDB [db1]> select * from t2;
+------+
| x |
+------+
| 0 | -1存成了0
| 0 | #无符号，最小值为0
| 255 | #无符号，最大值为255
| 255 | #256存成了255
+------+
============有符号和无符号int=============
#int默认为有符号
MariaDB [db1]> create table t3(x int); #默认为有符号整数
MariaDB [db1]> insert into t3 values
-> (-2147483649),
-> (-2147483648),
-> (2147483647),
-> (2147483648);
MariaDB [db1]> select * from t3;
+-------------+
| x |
+-------------+
| -2147483648 | #-2147483649存成了-2147483648
| -2147483648 | #有符号，最小值为-2147483648
| 2147483647 | #有符号，最大值为2147483647
| 2147483647 | #2147483648存成了2147483647
+-------------+
#设置无符号int
MariaDB [db1]> create table t4(x int unsigned);
MariaDB [db1]> insert into t4 values
-> (-1),
-> (0),
-> (4294967295),
-> (4294967296);
MariaDB [db1]> select * from t4;
+------------+
| x |
+------------+
| 0 | #-1存成了0
| 0 | #无符号，最小值为0
| 4294967295 | #无符号，最大值为4294967295
| 4294967295 | #4294967296存成了4294967295
+------------+
==============有符号和无符号bigint=============
MariaDB [db1]> create table t6(x bigint);
MariaDB [db1]> insert into t5 values
-> (-9223372036854775809),
-> (-9223372036854775808),
-> (9223372036854775807),
-> (9223372036854775808);
MariaDB [db1]> select * from t5;
+----------------------+
| x |
+----------------------+
| -9223372036854775808 |
| -9223372036854775808 |
| 9223372036854775807 |
| 9223372036854775807 |
+----------------------+
MariaDB [db1]> create table t6(x bigint unsigned);
MariaDB [db1]> insert into t6 values
-> (-1),
-> (0),
-> (18446744073709551615),
-> (18446744073709551616);
MariaDB [db1]> select * from t6;
+----------------------+
| x |
+----------------------+
| 0 |
| 0 |
| 18446744073709551615 |
| 18446744073709551615 |
+----------------------+
======用zerofill测试整数类型的显示宽度=============
MariaDB [db1]> create table t7(x int(3) zerofill);
MariaDB [db1]> insert into t7 values
-> (1),
-> (11),
-> (111),
-> (1111);
MariaDB [db1]> select * from t7;
+------+
| x |
+------+
| 001 |
| 011 |
| 111 |
| 1111 | #超过宽度限制仍然可以存
+------+Note: when specifying the width of that type, just display width specified query results, regardless of the storage range, the following range of storage
In fact, we do not need to specify the display width of an integer type, default on it
The default display width, are added to a maximum value on the basis of
Int memory width is 4 Bytes, i.e., 32 bit, i.e. 2 ** 32
Unsigned maximum value is: 4294967296-1
Signed maximum: 2147483648-1
Signed and unsigned largest digital display width required is 10, while the minimum for a signed 11 will need to show complete, so the default display type int width of 11 is very reasonable
Finally: plastic types, in fact, not necessary to specify the display width, using the default on ok
2, float
DEC fixed point type equivalent to DECIMAL
Floating-point type: FLOAT DOUBLE
Role: storage salary, height, weight, and other physical parameters
======================================
#FLOAT[(M,D)] [UNSIGNED] [ZEROFILL]
定义：
单精度浮点数（非准确小数值），m是数字总个数，d是小数点后个数。m最大值为255，d最大值为30
有符号：
-3.402823466E+38 to -1.175494351E-38,
1.175494351E-38 to 3.402823466E+38
无符号：
1.175494351E-38 to 3.402823466E+38
精确度：
**** 随着小数的增多，精度变得不准确 ****
======================================
#DOUBLE[(M,D)] [UNSIGNED] [ZEROFILL]
定义：
双精度浮点数（非准确小数值），m是数字总个数，d是小数点后个数。m最大值为255，d最大值为30
有符号：
-1.7976931348623157E+308 to -2.2250738585072014E-308
2.2250738585072014E-308 to 1.7976931348623157E+308
无符号：
2.2250738585072014E-308 to 1.7976931348623157E+308
精确度：
****随着小数的增多，精度比float要高，但也会变得不准确 ****
======================================
decimal[(m[,d])] [unsigned] [zerofill]
定义：
准确的小数值，m是数字总个数（负号不算），d是小数点后个数。 m最大值为65，d最大值为30。
精确度：
**** 随着小数的增多，精度始终准确 ****
对于精确数值计算时需要用此类型
decaimal能够存储精确值的原因在于其内部按照字符串存储。verification
mysql> create table t1(x float(256,31));
ERROR 1425 (42000): Too big scale 31 specified for column 'x'. Maximum is 30.
mysql> create table t1(x float(256,30));
ERROR 1439 (42000): Display width out of range for column 'x' (max = 255)
mysql> create table t1(x float(255,30)); #建表成功
Query OK, 0 rows affected (0.02 sec)
mysql> create table t2(x double(255,30)); #建表成功
Query OK, 0 rows affected (0.02 sec)
mysql> create table t3(x decimal(66,31));
ERROR 1425 (42000): Too big scale 31 specified for column 'x'. Maximum is 30.
mysql> create table t3(x decimal(66,30));
ERROR 1426 (42000): Too-big precision 66 specified for 'x'. Maximum is 65.
mysql> create table t3(x decimal(65,30)); #建表成功
Query OK, 0 rows affected (0.02 sec)
mysql> show tables;
+---------------+
| Tables_in_db1 |
+---------------+
| t1 |
| t2 |
| t3 |
+---------------+
rows in set (0.00 sec)
mysql> insert into t1 values(1.1111111111111111111111111111111); #小数点后31个1
Query OK, 1 row affected (0.01 sec)
mysql> insert into t2 values(1.1111111111111111111111111111111);
Query OK, 1 row affected (0.00 sec)
mysql> insert into t3 values(1.1111111111111111111111111111111);
Query OK, 1 row affected, 1 warning (0.01 sec)
mysql> select * from t1; #随着小数的增多，精度开始不准确
+----------------------------------+
| x |
+----------------------------------+
| 1.111111164093017600000000000000 |
+----------------------------------+
row in set (0.00 sec)
mysql> select * from t2; #精度比float要准确点，但随着小数的增多，同样变得不准确
+----------------------------------+
| x |
+----------------------------------+
| 1.111111111111111200000000000000 |
+----------------------------------+
row in set (0.00 sec)
mysql> select * from t3; #精度始终准确,d为30，于是只留了30位小数
+----------------------------------+
| x |
+----------------------------------+
| 1.111111111111111111111111111111 |
+----------------------------------+
row in set (0.00 sec)