MySQL query returns 0 rows when searching for value with dot (.) in string

问题

If I try to search for a value in mysql database and the string value contains dot in it, query returns 0 rows. Example:

SELECT * FROM table WHERE `username`='marco.polo'  --> 0 rows
SELECT * FROM table WHERE `username` LIKE '%.polo%'  --> 0 rows
SELECT * FROM table WHERE `username` LIKE 'polo'  --> Success

This appeared after moving server and database to another place. I know that dot is a set of extended regular expressions, but it should not apply to equal nor LIKE operator, simply because I don't use REGEXP in query.

I've tested the same query on my local database and it works fine. Could there be a special setting in mysql that treats dot differently than it usually does?

回答1:

user1084605, I tried to replicate the problem (using MySQL version 5.1.37), but got exactly the opposite results as you. See below:

mysql> create table test (username varchar(100));
Query OK, 0 rows affected (0.01 sec)

mysql> insert into test values ('marco.polo');
Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM test WHERE `username`='marco.polo';
+------------+
| username   |
+------------+
| marco.polo | 
+------------+
1 row in set (0.00 sec)

mysql> SELECT * FROM test WHERE `username` LIKE '%.polo%';
+------------+
| username   |
+------------+
| marco.polo | 
+------------+
1 row in set (0.00 sec)

mysql> SELECT * FROM test WHERE `username` LIKE 'polo';
Empty set (0.00 sec)

According to the MySQL docs, the only special characters when using the LIKE operator are "%" (percent: matches 0, 1, or many characters) and "_" (underscore: matches one and only one character). http://dev.mysql.com/doc/refman/5.0/en/string-comparison-functions.html

A "." (period) does have special meaning for MySQL's REGEXP operator, but it should still match a literal period in your column. http://dev.mysql.com/doc/refman/5.0/en/regexp.html

Can you replicate the SQL statements I ran above and paste your results in reply?

回答2:

As @cen already mentioned, character set can causes that problem. I have had this sample:

`email` VARCHAR(45) CHARACTER SET 'armscii8' NOT NULL,

this is was in the .sql dump, which I receive.

So, when I was trying to fetch object with this email I couldn't get it.

回答3:

The below query takes care of the scenario when we have only DOT operator in the columns.

 SELECT * FROM test WHERE `username` LIKE '%.%';

来源：https://stackoverflow.com/questions/8408905/mysql-query-returns-0-rows-when-searching-for-value-with-dot-in-string

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