Data types for database forms

Database type of column:  

Currently, there are only 2 kinds of types: int, char  

Column type:

1. Number types

2. String type

3. Date type

Integer type in number type:

Tinyint of 1 bytes -128~127

SmallInt of 2 bytes -32768~32767

Mediumint of 3 bytes-8388608 ~ 8388607

int accounted for 4 bytes -2147483648~2147483647

BigInt occupies 8 bytes anyway the range is larger than int.

How do you choose these integer types when you use them in peacetime? Choose according to your business needs.

When we define a column type, we can also indicate unsigned.

All the columns of the T1 table are now unsigned.

At this point the unsigned case:

Tinyint of 1 bytes 0~255

SmallInt of 2 bytes 0~65535

Other slightly.

Supplement: 0 padding. The key word is Zerofill

Floating-point types:

Float accounts for 4 bytes and 7 digits in a valid number.

Double is a valid number of 8 bytes 15~16 digits.

Note that the result shows that the precision is lost because of the float and double significant digits.

What to note about floating-point types:

1. You can specify the number of columns that float and doouble are integers, and the number of columns that the decimals occupy.

Floating-point numbers also support scientific notation:

12345678 = 1.2345678e7

123456 = 1.23456e5

If you deal with money, you must not use float and double to deposit money. This leads to the one type: fixed-point number: decimal

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Data types for database forms