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How should I escape characters inside this LIKE query?
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I have a column called \'column. I am able to use it in SELECT statements just like any other column. However, when I try to perform SHOW COLUMNS FROM myTable LIKE '\\''column' I get no results. I observed that it works if I double escape the backslash: '\\\\''column'.
I tested this from MariaDB console, but I also observed the same behaviour in MySQL 8.
How does the escaping work? How should I properly escape the value so that I can fetch the column information?
DB Fiddle
From the mysql documentation
MySQL uses C escape syntax in strings (for example, \n to represent
the newline character). If you want a LIKE string to contain a literal
, you must double it. (Unless the NO_BACKSLASH_ESCAPES SQL mode is
enabled, in which case no escape character is used.) For example, to
search for \n, specify it as \\n. To search for \, specify it as \\\\;
this is because the backslashes are stripped once by the parser and
again when the pattern match is made, leaving a single backslash to be
matched against.
Related
This failed in Java 13 (JDBC) code so I went to MySQL Workbench to duplicate problem.
I run a simple query as:
START TRANSACTION;
SET SESSION sql_mode = NO_BACKSLASH_ESCAPES;
SELECT *, "x\\x", "y\y" from dirs
WHERE d_pathname like 'E:\\\\BOOKS\\\\Dictionaries_and_Encyclopedias\\\\%' ORDER BY d_pathname;
and I get 400 rows returned. The issue is, that I do not want to use double-backslashes.
Rows returned show a single backslash, not a double backslash.
Interestingly, the x\\x and y\y clauses appear just as represented in the SELECT statement.
When I remove the double backslashes in the LIKE clause, I get zero rows!
Why? I'd rather not have to double-up the backslashes, and run simple and clean code.
The NO_BACKSLASH_ESCAPES mode only affects how backslashes are treated in ordinary string literals. It doesn't change how they're processed in LIKE patterns.
However, you can use the ESCAPE option to specify a different character to use as the escape character in LIKE. Just use some other character that doesn't appear in your pattern.
WHERE d_pathname like 'E:\BOOKS\Dictionaries_and_Encyclopedias\%' ESCAPE '|'
I have written regex and tested it online, works fine. When I test in terminal, MySQL console, it doesn't match and I get an empty set. I believe MySQL regexp syntax is somehow different but I cannot find the right way.
This is data I use:
edu.ba;
medu.ba;
edu.ba;
med.edu.ba;
edu.com;
edu.ba
I should get only edu.ba matches including; if there is some. Works fine except in actual query.
(\;+|^)\bedu.ba\b(\;+|$|\n)
Is there anything I could change to get the same results?
You want to match edu.ba in between semi-colons or start/end of string. The word boundaries are redundant here (although if you want to experiment, the MySQL regex before MySQL v8 used [[:<:]] / [[:>:]] word boundaries, and in MySQL v8+, you need to use double backslashes with \b - '\\b').
Use
(;|^)edu[.]ba(;|$)
Details
(;|^) - ; or start of string
edu[.]ba - edu.ba literal string (dot inside brackets always matches a literal dot)
(;|$) - ; or end of string.
Consider the following regex
#(.*\..*){2,}
Expected behaviour:
a#b doesnt match
a#b.c doesnt match
a#b.c.d matches
a#b.c.d.e matches
and so on
Testing in regexpal it works as expected.
Using it it in a mysql select doesn't work as expected. Query:
SELECT * FROM `users` where mail regexp '#(.*\..*){2,}'
is returning lines like
foo#example.com
that should not match the given regex. Why?
I think the answer to your question is here.
Because MySQL uses the C escape syntax in strings (for example, “\n”
to represent the newline character), you must double any “\” that you
use in your REGEXP strings.
MYSQL Reference
Because your middle dot wasn't properly escaped it was treated as just another wildcard and in the end your expression was effectively collapsed to #.{2,} or #..+
#anubhava's answer is probably a better substitute for what you tried to do though I would note #dasblinkenlight's comment about using the character class [.] which will make it easy to drop in a regex you've already tested in at RegexPal.
You can use:
SELECT * FROM `users` where mail REGEXP '([^.]*\\.){2}'
to enforce at least 2 dots in mail column.
I would match two dots in MySQL using like:
where col like '%#.%.%'
The problem with your code is that .* (match-everything dot) matches dot '.' character. Replacing it with [^.]* fixes the problem:
SELECT *
FROM `users`
where mail regexp '#([^.]*[.]){2,}'
Note the use of [.] in place of the equivalent \.. This syntax makes it easier to embed the regex into programming languages that use backslash as escape character in their string literals.
Demo.
I tried running this query:
SELECT column FROM table WHERE column REGEXP '[^A-Za-z\-\']'
but this returns
#1139 - Got error 'invalid character range' from regexp
which seems to me like the - in the character class is not being escaped, and instead read as an invalid range. Is there some other way that it's suppose to be escaped for mysql to be the literal -?
This regex works as expected outside of mysql, https://regex101.com/r/wE8vY5/1.
I came up with an alternative to that regex which is
SELECT column FROM table WHERE column NOT REGEXP '([:alpha:]|-|\')'
so the question isn't how do I get this to work. The question is why doesn't the first regex work?
Here's a SQL fiddle of the issue, http://sqlfiddle.com/#!9/f8a006/1.
Also, there is no language being used here, query is being run at DB level.
Regex in PHP: http://sandbox.onlinephpfunctions.com/code/10f5fe2939bdbbbebcc986c171a97c0d63d06e55
Regex in JS: https://jsfiddle.net/6ay4zmrb/
Just change the order.
SELECT column FROM table WHERE column REGEXP '[^-A-Za-z\']'
#Avinash Raj is correct the - must be first (or last). The \ is not an escape character in POSIX, which is what mysql uses, https://dev.mysql.com/doc/refman/5.1/en/regexp.html.
One key syntactic difference is that the backslash is NOT a metacharacter in a POSIX bracket expression.
-http://www.regular-expressions.info/posixbrackets.html
What special characters must be escaped in regular expressions?
Inside character classes, the backslash is a literal character in POSIX regular expressions. You cannot use it to escape anything. You have to use "clever placement" if you want to include character class metacharacters as literals. Put the ^ anywhere except at the start, the ] at the start, and the - at the start or the end of the character class to match these literally
I'm attempting to query our MSSQL database but I'm getting no data when there clearly is data there.
First I query
SELECT id, instruction_link FROM work_instructions WHERE instruction_link LIKE "%\\\\cots-sbs%";
Which returns 100+ lines.
http://tinypic.com/r/ief8td/8
(sorry couldn't post as actual picture, don't have enough rep :(
However if I query
SELECT id, instruction_link FROM work_instructions WHERE instruction_link LIKE "%\\\\cots-sbs\\%";
http://tinypic.com/r/33ksw3q/8
I get no results with the 2nd query. I have no idea what I'm doing wrong here. Seems pretty simple but I can't make any sense of it..
Thanks in advance.
As documented under LIKE:
Note
Because MySQL uses C escape syntax in strings (for example, “\n” to represent a newline character), you must double any “\” that you use in LIKE strings. For example, to search for “\n”, specify it as “\\n”. To search for “\”, specify it as “\\\\”; this is because the backslashes are stripped once by the parser and again when the pattern match is made, leaving a single backslash to be matched against.
\\% is parsed as a string containing a literal backslash followed by a percentage character, which is then interpreted as a pattern containing only a literal percentage sign.