MySql：向空值添加非空约束传递？

Question

I have a JUnit test for some mysql code which passes locally but fails when run on the server. Locally I am using Windows 7 and the server is Ubuntu 14.04. Both are running MySql 5.6.

I have a char column with a null value and try and put a not null constraint on it. Locally this fails as it should but on the server I only get a warning but it passes and the null value is set to a empty string. (See images) I assume this is some difference in mysql server configuration? I am new to MySql and can't find how to fix this.

Example image: up is server, down is local:

Answer 1

First check:

SELECT @@sql_mode;

You probably get:

STRICT_TRANS_TABLES/STRICT_ALL_TABLES


UP env :   -------
DOWN env:   STRICT_..._TABLES

The difference is Error vs Warning :

Modes :

Strict mode controls how MySQL handles invalid or missing values in data-change statements such as INSERT or UPDATE. A value can be invalid for several reasons. For example, it might have the wrong data type for the column, or it might be out of range. A value is missing when a new row to be inserted does not contain a value for a non-NULL column that has no explicit DEFAULT clause in its definition. (For a NULL column, NULL is inserted if the value is missing.)

SqlFiddleDemo

The correct way to solve it is first to update NULL to empty string before altering schema.

CREATE TABLE test_table(primary_key INT AUTO_INCREMENT PRIMARY KEY,
                        short_char CHAR(100));

INSERT INTO test_table(short_char)
VALUES (NULL);

UPDATE test_table
SET short_char = ''
WHERE short_char IS NULL;

ALTER TABLE test_table modify short_char char(100) not null;

SqlFiddleDemo2

I recommend to use VARCHAR(100) instead of CHAR(100) .