I just found myself lost in the interesting situation that I need to query MySQL for fields containing a so called Left-to-right mark.
As the nature of this character is to be non-printing, thus invisible, I'm unable to simply copy/paste it into a query.
As mentioned in the linked Wikipedia article, the Left-to-right mark is Unicode character U+200F, which is a fact that I'm sure is the key to success in my current adventure.
My question is: How do I use raw Unicode in a MySQL query? Something along the lines of:
SELECT * FROM users WHERE username LIKE '%\U+200F%'
or
SELECT * FROM users WHERE username REGEXP '\U+200F'
or whatever the correct syntax for Unicode in MySQL is and depending on whether this is supported with LIKE and/or REGEXP.
To get a unicode char, something like this should work:
SELECT CHAR(<number> USING utf8);
Also, don't use REGEXP, because the regexp lib used by MySQL is very old, and doesn't support multi-byte charsets.
Related
Is it possible to search by Unicode range in MySQL? I have used this before, and I thought it worked:
SELECT * FROM people where surname NOT REGEXP "[\u0020\u0027\u002D\u0041-\uFF5A]"
The RegEx will find any surnames not composed of Latin characters, spaces, apostrohpes and hyphens, but it is not working on a table I am testing now.
From what I am reading, it seems this is not possible. If so, are there any workarounds? Such as specifying all the characters manually, e.g.
SELECT * FROM people where surname NOT REGEXP "[ -'abcdefg...]"
UPDATE: The above is an acceptable solution.
An old-yet-important question that was answered by #Mofi's comment:
On MySql 8.0 and above, the Unicode prefix \u should be escaped: \\u.
So, for example, to search for the range a-z:
SELECT * FROM people where surname REGEXP "[\\u0061-\\u007a]"
On earlier versions, using Unicode is unsupported (see this question), and what actually happens is a set match, e.g. for [\\u0061], strings containing u, 0, 6 or 1 are matched.
You can try it out with a fiddle that has both new & old version, like this one, and see for yourself.
We have some tables that were set with the Latin character set instead of UTF-8 and it allowed bad characters to be entered into the tables, the usual culprit is people copy / pasting from Word or Outlook which copys those nasty hidden characters...
Is there any query we can use to identify these characters to clean them?
Thanks,
I assume that your connection chacater set was set to UTF8 when you filled the data in.
MySQL replaces unconvertable characters with ? (question marks):
SELECT CONVERT('тест' USING latin1);
----
????
The problem is distinguishing legitimate question marks from illegitimate ones.
Usually, the question marks in the beginning of a word are a bad sign, so this:
SELECT *
FROM mytable
WHERE myfield RLIKE '\\?[[:alnum:]]'
should give a good start.
You're probably noticing something like this 'bug'. The 'bad characters' are most likely UTF-8 control characters (eg \x80). You might be able to identify them using a query like
SELECT bar FROM foo WHERE bar LIKE LOCATE(UNHEX(80), bar)!=0
From that linked bug, they recommend using type BLOB to store text from windows files:
Use BLOB (with additional encoding field) instead of TEXT if you need to store windows files (even text files). Better than 3-byte UTF-8 and multi-tier encoding overhead.
Take a look at this Q/A (it's all about your client encoding aka SET NAMES )
I have a MySQL table with two columns, both utf8_unicode_ci collated. It contains the following rows. Except for ASCII, the second field also contains Unicode codepoints like U+02C8 (MODIFIED LETTER VERTICAL LINE) and U+02D0 (MODIFIED LETTER TRIANGULAR COLON).
word | ipa
--------+----------
Hallo | haˈloː
IPA | ˌiːpeːˈʔaː
I need to search the second field with LIKE and REGEXP, but MySQL (5.0.77) seems to interpret these fields as bytes, not as characters.
SELECT * FROM pronunciation WHERE ipa LIKE '%ha?lo%'; -- 0 rows
SELECT * FROM pronunciation WHERE ipa LIKE '%ha??lo%'; -- 1 row
SELECT * FROM pronunciation WHERE ipa REGEXP 'ha.lo'; -- 0 rows
SELECT * FROM pronunciation WHERE ipa REGEXP 'ha..lo'; -- 1 row
I'm quite sure that the data is stored correctly, as it seems good when I retrieve it and shows up fine in phpMyAdmin. I'm on a shared host, so I can't really install programs.
How can I solve this problem? If it's not possible: is there a plausible work-around that does not involve processing the entire database with PHP every time? There are 40 000 lines, and I'm not dead-set on using MySQL (or UTF8, for that matter). I only have access to PHP and MySQL on the host.
Edit: There is an open 4-year-old MySQL bug report, Bug #30241 Regular expression problems, which notes that the regexp engine works byte-wise. Thus, I'm looking for a work-around.
EDITED to incorporate fix to valid critisism
Use the HEX() function to render your bytes to hexadecimal and then use RLIKE on that, for example:
select * from mytable
where hex(ipa) rlike concat('(..)*', hex('needle'), '(..)*'); -- looking for 'needle' in haystack, but maintaining hex-pair alignment.
The odd unicode chars render consistently to their hex values, so you're searching over standard 0-9A-F chars.
This works for "normal" columns too, you just don't need it.
p.s. #Kieren's (valid) point addressed using rlike to enforce char pairs
I'm not dead-set on using MySQL
Postgres seems to handle it quite fine:
test=# select 'ˌˈʔ' like '___';
?column?
----------
t
(1 row)
test=# select 'ˌˈʔ' ~ '^.{3}$';
?column?
----------
t
(1 row)
If you go down that road, note that in Postgres' ilike operator matches that of MySQL's like. (In Postgres, like is case-sensitive.)
For the MySQL-specific solution, you mind be able to work around by binding some user-defined function (maybe bind the ICU library?) into MySQL.
You have problems with UTF8? Eliminate them.
How many special characters do you use? Are you using only locase letters, am I right? So, my tip is: Write a function, which converts spec chars to regular chars, e.g. "æ" ->"A" and so on, and add a column to the table which stores that converted value (you have to convert all values first, and upon each insert/update). When searching, you just have to convert search string with the same function, and use it on that field with regexp.
If there're too many kind of special chars, you should convert it to multi-char. 1. Avoid finding "aa" in the "ba ab" sequence use some prefix, like "#ba#ab". 2. Avoid finding "#a" in "#ab" use fixed length tokens, say, 2.
I have a couple escaped characters in user-entered fields that I can't figure out.
I know they are the "smart" single and double quotes, but I don't know how to search for them in mysql.
The characters in ruby, when output from Ruby look like \222, \223, \224 etc
irb> "\222".length => 1
So - do you know how to search for these in mysql? When I look in mysql, they look like '?'.
I'd like to find all records that have this character in the text field. I tried
mysql> select id from table where field LIKE '%\222%'
but that did not work.
Some more information - after doing a mysqldump, this is how one of the characters is represented - '\\xE2\\x80\\x99'. It's the smart single quote.
Ultimately, I'm building an RTF file and the characters are coming out completely wrong, so I'm trying to replace them with 'dumb' quotes for now. I was able to do a gsub(/\222\, "'").
Thanks.
I don't quite understand your problem but here is some info for you:
First, there are no escaped characters in the database. Because every character being stored as is, with no escaping.
they don't "look ilke ?". I's just wrong terminal settings. SET NAMES query always should be executed first, to match client encoding.
you have to determine character set and use it on every stage - in the database, in the mysql client, in ruby.
you should distinguish ruby strings representation from character itself.
To enter character in the mysql query, you can use char function. But in terminal only. In ruby just use the character itself.
smart quotes looks like 2-byte encoded in the unicode. You have to determine your encoding first.
I'm working with a MySQL database that has some data imported from Excel. The data contains non-ASCII characters (em dashes, etc.) as well as hidden carriage returns or line feeds. Is there a way to find these records using MySQL?
MySQL provides comprehensive character set management that can help with this kind of problem.
SELECT whatever
FROM tableName
WHERE columnToCheck <> CONVERT(columnToCheck USING ASCII)
The CONVERT(col USING charset) function turns the unconvertable characters into replacement characters. Then, the converted and unconverted text will be unequal.
See this for more discussion. https://dev.mysql.com/doc/refman/8.0/en/charset-repertoire.html
You can use any character set name you wish in place of ASCII. For example, if you want to find out which characters won't render correctly in code page 1257 (Lithuanian, Latvian, Estonian) use CONVERT(columnToCheck USING cp1257)
You can define ASCII as all characters that have a decimal value of 0 - 127 (0x00 - 0x7F) and find columns with non-ASCII characters using the following query
SELECT * FROM TABLE WHERE NOT HEX(COLUMN) REGEXP '^([0-7][0-9A-F])*$';
This was the most comprehensive query I could come up with.
It depends exactly what you're defining as "ASCII", but I would suggest trying a variant of a query like this:
SELECT * FROM tableName WHERE columnToCheck NOT REGEXP '[A-Za-z0-9]';
That query will return all rows where columnToCheck contains any non-alphanumeric characters. If you have other characters that are acceptable, add them to the character class in the regular expression. For example, if periods, commas, and hyphens are OK, change the query to:
SELECT * FROM tableName WHERE columnToCheck NOT REGEXP '[A-Za-z0-9.,-]';
The most relevant page of the MySQL documentation is probably 12.5.2 Regular Expressions.
This is probably what you're looking for:
select * from TABLE where COLUMN regexp '[^ -~]';
It should return all rows where COLUMN contains non-ASCII characters (or non-printable ASCII characters such as newline).
One missing character from everyone's examples above is the termination character (\0). This is invisible to the MySQL console output and is not discoverable by any of the queries heretofore mentioned. The query to find it is simply:
select * from TABLE where COLUMN like '%\0%';
Based on the correct answer, but taking into account ASCII control characters as well, the solution that worked for me is this:
SELECT * FROM `table` WHERE NOT `field` REGEXP "[\\x00-\\xFF]|^$";
It does the same thing: searches for violations of the ASCII range in a column, but lets you search for control characters too, since it uses hexadecimal notation for code points. Since there is no comparison or conversion (unlike #Ollie's answer), this should be significantly faster, too. (Especially if MySQL does early-termination on the regex query, which it definitely should.)
It also avoids returning fields that are zero-length. If you want a slightly-longer version that might perform better, you can use this instead:
SELECT * FROM `table` WHERE `field` <> "" AND NOT `field` REGEXP "[\\x00-\\xFF]";
It does a separate check for length to avoid zero-length results, without considering them for a regex pass. Depending on the number of zero-length entries you have, this could be significantly faster.
Note that if your default character set is something bizarre where 0x00-0xFF don't map to the same values as ASCII (is there such a character set in existence anywhere?), this would return a false positive. Otherwise, enjoy!
Try Using this query for searching special character records
SELECT *
FROM tableName
WHERE fieldName REGEXP '[^a-zA-Z0-9#:. \'\-`,\&]'
#zende's answer was the only one that covered columns with a mix of ascii and non ascii characters, but it also had that problematic hex thing. I used this:
SELECT * FROM `table` WHERE NOT `column` REGEXP '^[ -~]+$' AND `column` !=''
In Oracle we can use below.
SELECT * FROM TABLE_A WHERE ASCIISTR(COLUMN_A) <> COLUMN_A;
for this question we can also use this method :
Question from sql zoo:
Find all details of the prize won by PETER GRÜNBERG
Non-ASCII characters
ans: select*from nobel where winner like'P% GR%_%berg';