Data problems can also be found if there is a space at the end of the field value of MySQL query criteria

1、 Problem description

I encountered a problem in my work today , The production environment has a null pointer exception when calling a scheduled task , After investigation, it was found that mysql Data can also be found if there is a space at the end of the field value of the query criteria . and map in key Is a value with spaces , If you can't get the null pointer . Here's a replay

Here are two people with the same name in my library , A name followed by a space , A name without spaces . This 1 To see the blank space effect in the screenshot

SELECT * FROM `student` where studentname = ' Zhang Wei ';

Here, the person who queries the field without spaces will query the person who has spaces at the end of the field

Here is the person with a space at the end of the query field

SELECT * FROM `student` where studentname = ' Zhang Wei  ';

Query results

2、 Question why

The reason for this problem is ： If the field is char or varchar type , So when comparing strings MySQL Use PADSPACE Proofread rules , The space character at the end of the field is ignored , Whether it is followed by a space or multiple

3、 The solution to the problem

3.1、 from SQL To solve the problem

1. Use the compared value BINARY Function to binary

SELECT * FROM `student` where studentname = BINARY' Zhang Wei ';

2. Use length Function to compare （ Large quantities of data will affect efficiency ）

SELECT * FROM `student` where studentname = ' Zhang Wei ' and LENGTH(studentname) = LENGTH(' Zhang Wei ');

3. Use like function

SELECT * FROM `student` where studentname like ' Zhang Wei ';

3.2、 from Java Aspect avoidance

from Java The way to avoid this aspect is to use the time string input parameter of the query trim() Method to remove white space , At the same time, the results of the query should also deal with spaces