MySQL Boolean “tinyint(1)” holds values up to 127?

问题

I wanted to make a true/false field for if an item is in stock.

I wanted to set it to Boolean ( which gets converted to tinyint(1) ), 1 for in stock, 0 for not in stock.

I am getting feeds from vendors, so I thought to myself, "What if they pass how many are instock?"

So I wondered if I inserted a number higher than 1 what would happen. I assumed it would default to 1.

To my surprise it will allow me to hold any number up to 127, anything over defaults to 127.

Can anyone explain why?

回答1:

The signed TINYINT data type can store integer values between -128 and 127.

However, TINYINT(1) does not change the minimum or maximum value it can store. It just says to display only one digit when values of that type are printed as output.

回答2:

The tinyint data type utilizes 1 byte of storage. 256 possible integer values can be stored using 1 byte (-128 through 127). if you define as tinyint unsigned then negative values are discarded so is possible to store (0 through 255).

回答3:

See here for how MySQL handles this. If you use MySQL > 5.0.5 you can use BIT as data type (in older versions BIT will be interpreted as TINYINT(1). However, the (1)-part is just the display width, not the internal length.

回答4:

CREATE TABLE foo_test(
col_1 TINYINT
, col_2 TINYINT(2) 
, col_3 TINYINT(3) 
, col_4 TINYINT(2) ZEROFILL
, col_5 TINYINT(3) ZEROFILL
);

INSERT INTO foo_test( col_1,col_2,col_3,col_4,col_5 )
SELECT 1, 1,1,1,1
UNION ALL
SELECT 10, 10,10,10,10
UNION ALL
SELECT 100, 100,100,100,100;

SELECT * FROM foo_test; 

**OUTPUT:-**   
 col_1   col_2   col_3   col_4   col_5  
------  ------  ------  ------  --------
     1       1       1      01       001
    10      10      10      10       010
   100     100     100     100       100

MySQL will show the 0's in the start if zerofill is used while creating the table. If you didn't use the zerofill then it is not effective.

来源：https://stackoverflow.com/questions/4401673/mysql-boolean-tinyint1-holds-values-up-to-127

标签

mysql

boolean

tinyint