I have a table:
CREATE TABLE `ids` (
id int(11) not null auto_increment,
PRIMARY KEY (id)
);
It contains some IDs: 111, 112, 113, 114 etc.
I made a query:
SELECT * FROM `ids` WHERE id = '112abcdefg'
I expected nothing but I've got a result, a row with ID of 112. Seems that MySQL quietly converted my string to integer and then compared it against column values.
How can I change the query so that querying the same string from id column will give no results as I expect? Is there a strict comparison modifier in MySQL?
One option is to CAST the 112 to CHAR to get a proper match:
WHERE CAST(id AS CHAR(12)) = '112abcdefg'
The 12 in CHAR is a guess; it should be large enough for your biggest id.
That will probably kill any chance of optimization, so another option (though one I'm not 100% sure of) is to use a BINARY comparison. I've tried this with a few different values and it works:
WHERE BINARY id = '112abcdefg'
You are comparing a string, just put the number with no quotes:
SELECT * FROM `ids` WHERE id = 112
If you dont, it will convert the string '112abcdefg' to a number and say its 112
The response you are seeing is because you are trying to compare an integer column to a string value. In that case, MySQL will type-cast the string literal value to an integer, and when it does that it starts from the left of the string and as soon as it reaches a character that cannot be considered part of a number, it strips out everything from that point on. So trying to compare "256abcd" to an integer column will result in actually comparing the number 256.
So your options (or at least a few of them) would be:
Validate the input string in your application code and reject it if it's not an integer (see the ctype_digit function in PHP).
Change the column type for the filename if you want to treat it as a string (e.g. a VARCHAR type).
Cast the column value to a string:
. . . WHERE CAST(Id AS CHAR) = '256aei'
Source
you can use this :
SET sql_mode = STRICT_TRANS_TABLES;
this sets you sql mode to strict checking, and then try firing the query you mentioned.
lame + kills optimization but serves it purpose
SELECT * FROM `ids` WHERE concat(id) = '112abcdefg';
that way you enforce casting to string
http://dev.mysql.com/doc/refman/5.1/en/type-conversion.html
Related
I have a table which primary key is numeric and auto-incremented.
When I run a query such as:
SELECT * FROM my_table where id = '1a';
The query returns the row with the primary key set to "1".
I was not aware of this behavior, is it possible to prevent it?
I was expecting this WHERE clause to retrieve nothing since the id is "1" and not "1a". It is behaving like it was a LIKE clause.
MySQL implicitly converts a String literal to int while comparing with an int column.
You should really fix your application code (eg: PHP), and properly typecast to (int) before using them in a query. Ideally, your application should not have been inputting string values to compare against an integer field.
Now still, if you don't have control over input value, an approach can be to check if the value is numeric or not, and use it accordingly for comparison. Adapting a sargable approach from https://dba.stackexchange.com/q/89760/160363
SELECT * FROM my_table
WHERE id = CASE WHEN CONCAT('','1a'*1) = '1a' THEN '1a' ELSE NULL END;
mysql automatically converts strings to numbers, and just takes the leading characters that are digits. You could instead explicitly cast the ID to a string:
SELECT * FROM my_table where CAST(id AS CHAR) = '1a';
I'm using MySQL 8 with InnoDB with a node server with mysql2 driver.
My table looks like:
CREATE TABLE IF NOT EXISTS users(
id VARCHAR(36) NOT NULL,
name VARCHAR(32) NOT NULL,
email VARCHAR(255) NOT NULL,
...
PRIMARY KEY (id)
)
I use no auto increment and as VARCHAR ids, I use time based UUIDs.
If I now do my SELECT query:
SELECT * FROM users where id = 'some valid id';
I get my expected result.
If I do:
SELECT * FROM users where id = '0';
I get nothing, because no id in my table has the value '0'.
BUT, if i do:
SELECT * FROM users where id = 0;
I get the last inserted row, which has, of course, a valid VARCHAR id different from 0.
This behavior occured on my node server by accident, because JS sometimes interpretes undefined as 0 in http querys.
In consequence I can easyly avoid inserting 0 in my querys (what I do now), but I would like to understand why this happens.
Your id is varchar(), so this comparison:
WHERE id = 0
requires type conversion.
According to the conversion rules in SQL, the id is turned into a string. Now, in many databases, you would get an error if any values of id could not be converted into numbers.
However, MySQL supports implicit conversion with no errors. (You can read about such conversion in the documentation.) This converts all leading digits to a number -- ignoring the rest. If there are no leading digits, then the value is zero. So, all these are true in MySQL:
'a' = 0
'0a' = 0'
'anything but 0!' = 0
There are two morals to this story.
If you really want id to be a number, then use a number data type (int, bigint, decimal).
Don't mix types in comparisons.
I am trying to clean the telephone numbers of a database so we can easily search for them. In the column TEL we have rows like:
654-598-5487
654.254.2456
(458)-5458789 e.3
I want to copy all those values to a new column where only the numeric characters are transferred:
6545985487
6542542456
45854587893
The new column (TEL_NO_FORMAT) is a big int and it only allows numbers, but if I execute something like this:
UPDATE CLIENTS set `TEL_NO_FORMAT` = `TEL`
It will only transfer the first numeric characters found and ignore the rest:
654
654
NULL
Easiest way is the REGEXP_REPLACE(MySQL 8.0+):
SELECT *, REGEXP_REPLACE(tel_no_format, '[^0-9]','') AS result
FROM clients
Answering the question in an update query
UPDATE CLIENTS SET TEL_NO_FORMAT = REGEXP_REPLACE(TEL, '[^0-9]','');
You should replace the undesired char before
UPDATE CLIENTS set `TEL_NO_FORMAT` = replace(replace(replace(`TEL`, '.',''),'-',''),')','')
because some char (eg '-') are create problem during conversion ..
anyway rember that a big int can't manage properly eventual tel number 0 prefixed eg:
00453778988
This happened when I was just testing.
I've created a table as
Create Table Test_Table
(
Field_char char(1)
);
When I want to insert value with code
Insert Into Test_Table(Field_char)
Select 13;
It inserts '*' in the column. For single digits it inserts them as it is. If the length is modified from 1 to 2, similar thing happen for 3 digits input such as 100 etc.
Why is this?
In your create statement you set the length of Field_char to 1 (char(1)). This means that your entries must have a length smaller or equal to 1. valid entries are 1,2 etc. Invalid entries are 12, 13 as they are longer than 1 char -> * is a placeholder to indicate invalid values.
EDIT: (Thanks To Vladimir)
To be more precise take a look here.
Truncating and Rounding Results
[...] Conversions to char, varchar, nchar, nvarchar, binary, and varbinary are truncated, except for the conversions shown in the following table.
There we have the following entry:
From data type int to data type char result *
where * = Result length too short to display
When you are writing
Insert Into Test_Table(Field_char)
Select 13;
The it is converting int to char. So your 13 is converted into *. If you want you can check by writing
select CONVERT(char(1),13)
If you want to see the result as 13 then you need to put that in single inverted comma like this:
Insert Into Test_Table(Field_char)
Select '13';
And also you need to increase the size of column as char(1) can hold only one character.
SQL FIDDLE DEMO
It simply Convert Int to Char
for Example
select CONVERT(char(1),13)
it will give *
Sql Implicitly convert int to char which is you column type..
I am writing a flexible search mechanism for a customer's website. I am utilizing union clauses to query a number of different fields in the database in search of a string value entered by the user. This works fine except for one issue.
When comparing a string of a text to an integer that is currently set to zero, the match always returns true. In other words, according to MySQL, "email#example.com" is equal to 0.
I have tried utilizing the CAST and CONVERT function to turn this into a standard string to string comparison, but I can't seem to get the syntax right. My attempts either repeat the above issue or return no rows at all when some should match. I am also concerned that doing this would have an effect on performance since I am combining lots of unions.
What I really need is a strict comparison between an entered string and the value in the database, be it an integer or string.
EDIT:
Here is an example.
CREATE TABLE `test_table` (
`id` INT NOT NULL AUTO_INCREMENT ,
`email` VARCHAR(255) NOT NULL ,
`phone` BIGINT(19) NOT NULL DEFAULT '0' ,
PRIMARY KEY (`id`) )
ENGINE = MyISAM;
INSERT INTO `test_table` (`id`, `email`, `phone`) VALUES (1, 'email#example.com', 0);
SELECT * FROM test_table WHERE phone = 'email#example.com';
Execute this and the one row that has been inserted will return. My issue is that it shouldn't!
This query should fail:
SELECT * FROM test_table WHERE cast(phone as char) = 'email#example.com';
The cause of the original problem is that when comparing strings and numbers, it converts the string to a number (so you can write where phone = '123'). You need to use an explicit cast of the field to make it a string-to-string comparison, to prevent this default conversion.
Unfortunately, casting like this is likely to prevent it from using indexes. Even if the field is already char, the cast apparently prevents it from indexing.
You could also solve it during input validation: if phone is an integer, don't allow the user to provide a non-integer value in the search field.
How about replacing:
SELECT * FROM test_table WHERE phone = 'email#example.com'
with:
SELECT * FROM test_table WHERE phone = 'email#example.com' and phone <> 0
<> means different from.
This will work for you because you are using 0 in the phone column to mean there isn't a phone number (although it would be better style to use NULL for no phone number).