I found this query in mysql query log and I will like to know what exactly does it do.
select * from tblname WHERE TRIM(NAME) REGEXP 'John[ ]*Smith'
It selects all rows from tblname where name (with spaces around removed, if any) equals to John<any number of spaces>Smith
So you'll find JohnSmith as well as John_________________________Smith (stackoverflow eats repetitive spaces, so I replaced them with underscore).
The regex itself is a little bloated and can be rewritten as John *Smith
Related
So I'm trying to find what "special characters" have been used in my customer names. I'm going through updating this query to find them all one-by-one, but it's still showing all customers with a - despite me trying to exlude that in the query.
Here's the query I'm using:
SELECT * FROM customer WHERE name REGEXP "[^\da-zA-Z\ \.\&\-\(\)\,]+";
This customer (and many others with a dash) are still showing in the query results:
Test-able Software Ltd
What am I missing? Based on that regexp, shouldn't that one be excluded from the query results?
Testing it on https://regex101.com/r/AMOwaj/1 shows there is no match.
Edit - So I want to FIND any which have characters other than the ones in the regex character set. Not exclude any which do have these characters.
Your code checks if the string contains any character that does not belong to the character class, while you want to ensure that none does belong to it.
You can use ^ and $ to check the while string at once:
SELECT * FROM customer WHERE name REGEXP '^[^\da-zA-Z .&\-(),]+$';
This would probably be simpler expressed with NOT, and without negating the character class:
SELECT * FROM customer WHERE name NOT REGEXP '[\da-zA-Z .&\-(),]';
Note that you don't need to escape all the characters within the character class, except probably for -.
Use [0-9] or [[:digit:]] to match digits irrespective of MySQL version.
Use the hyphen where it can't make part of a range construction.
Fix the expression as
SELECT * FROM customer WHERE name REGEXP "[^0-9a-zA-Z .&(),-]+";
If the entire text should match this pattern, enclose with ^ / $:
SELECT * FROM customer WHERE name REGEXP "^[^0-9a-zA-Z .&(),-]+$";
- implies a range except if it is first. (Well, after the "not" (^).)
So use
"[^-0-9a-zA-Z .&(),]"
I removed the + at the end because you don't really care how many; this way it will stop after finding one.
I have a SQL table, with genetic information (name of the gene, function, strand...)
I want to retrieve the amount of chromosomes (21 as I'm working with the human genome). Problem is that some chromosomes are "repeated". For example:
SELECT DISTINCT chrom FROM table LIMIT 6;
chr1
chr10
chr10_GL383545v1_alt
chr10_GL383546v1_alt
chr11
chr11_JH159136v1_alt
As you can see I have more than one chr10, so if I count the DISTINCT chromosomes I get about 6000.
I've tried using NOT LIKE "_" but didn't work. I've thought I could "force" the result with LIKE "chr1" and so on, but I feel like cheating and is not exactly what I'm searching for. I would like a way to avoid every "_", but running
SELECT COUNT(DISTINCT chrom) NOT LIKE "_" FROM table; gives me back just 1 result...
LEFT is not optimal either, because I would have to specify the length of the string, and, I want a system that I could use without knowing anything about the expected result. So running a LEFT "", 4 and LEFT "", 5 is not what I'm searching for.
Is there a way I can count everything that does NOT CONTAIN a certain character? There's a better strategy?
Thank you very much!
Underscore is a wildcard character itself, so it must be escaped. Furthermore you want to match any characters before and after that underscore character so the % wildcard is needed around the escaped underscore.
SELECT count(chrom) FROM table WHERE chrom NOT LIKE '%\_%`;
Also you could use substring_index() to get distinct string before the underscore and count those:
SELECT COUNT(DISTINCT SUBSTRING_INDEX(chrom, '_', 1)) FROM table;
Although that is almost definitely going to be slower.
The problem with SELECT COUNT(DISTINCT chrom) NOT LIKE "_" FROM table; is the location of the comparison and the lack of the % wildcards in the LIKE comparison string.
Either of the following should work for you:
SELECT COUNT(DISTINCT chrom) FROM table WHERE chrom NOT LIKE '%|_%' ESCAPE '|';
Using ESACPE and specifying an escape character after the LIKE is easier than using \ in many cases since, depending on your scenario, you may need to remember to double escape with \. (or if you are writing this in say php, triple escape)
SELECT COUNT(DISTINCT chrom) FROM table WHERE LOCATE('_', chrom) > 0;
LOCATE() is also easier to use here. But I believe it would be slower than just doing a LIKE. The performance difference is probably pretty insignificant, so in most cases, its just preference.
Use REGEXP if you wish to keep it simple.LIKE is faster though.
SELECT count(chrom) FROM table WHERE chrom NOT REGEXP '_';
I also recommend INSTR which I think will perform better than REGEXP.
SELECT count(chrom) FROM table WHERE INSTR(chrom, '_')=0;
I have two records with names bowser and Tommy in the table pet. Now when I run the following query in cmd nothing happen:
SELECT * FROM pet WHERE name LIKE '.%';
On the other hand the following query matches Bowser record:
SELECT * FROM pet WHERE name LIKE 'b%';
As far as I know, . should match any character. So '.%' should match every word.
Why is dot metacharactor of regex not working in mysql?
The reason your query doesn't work is because it is looking for names that start with a period. That is how LIKE works.
Use RLIKE or REGEXP:
WHERE name REGEXP '.*';
LIKE uses the ANSI standard for the operator. The equivalent of . is _. However, the way LIKE works is different from regular expressions.
The documentation does a good job of explaining the differences between LIKE and REGEXP.
So I have a table called "lu_regex" with a column called "regex"
Select * from lu_regex;
athedsl-\d+
i5[93][0-9a-fA-F]+\.versa
5ac[a-f0-9]+.+sky
The table contains 1000's of rows, with various Regular Expressions syntax, i'm just showing three in this example.
Now I'm trying to take user input and match that input against the rows in the table. So I'm doing this.
SELECT * FROM lu_regex where '5aca3a11.bb.sky.comr' regexp regex;
regex
5ac[a-f0-9]+.+sky
1 row returned.
I'm getting back what I expected, with that query, then I try this one.
SELECT * FROM lu_regex where 'athedsl-07371.home.otenet.gr' regexp regex;
0 rows returned.
It should match on "athedsl-\d+", but i'm assuming it has something to do with the "\d". I even tried adding this to the database "athedsl-\\d+" and that didn't cause a match either.
I'm trying to stick to a MySQL solution, what am I doing wrong, this should be possible.
I just found this link, it looks like a bug that hasn't been fixed. It was verified in 2013.
https://bugs.mysql.com/bug.php?id=70413
Bug #70413 \d is not working in REGEXP for a MySQL query
I think the solution is going to be is to replace all \d with [0-9]
I have a mysql table with a list of keywords such as:
id | keywords
---+--------------------------------
1 | apple, oranges, pears
2 | peaches, pineapples, tangerines
I'm trying to figure out how to query this table using an input string of:
John liked to eat apples
Is there a mysql query type that can query a field with a sentence and return results (in my example, record #1)?
One way to do it could be to convert apple, oranges, pears to apple|oranges|pears and use RLIKE (ie regular expression) to match against it.
For example, 'John liked to eat apples' matches the regex 'apple|orange|pears'.
First, to convert 'apple, oranges, pears' to the regex form, replace all ', ' by '|' using REPLACE. Then use RLIKE to select the keyword entries that match:
SELECT *
FROM keywords_table
WHERE 'John liked to eat apples' RLIKE REPLACE(keywords,', ','|');
However this does depend on your comma-separation being consistent (i.e. if there is one row that looks like apples,oranges this won't work as the REPLACE replaces a comma followed by a space (as per your example rows).
I also don't think it'll scale up very well.
And, if you have a sentence like 'John liked to eat pineapples', it would match both of the rows above (as it does have 'apple' in it). You could then try to add word boundaries to the regex (i.e. WHERE $sentence RLIKE '[[:<:]](apple|oranges|pears)[[:>:]]'), but this would screw up matching when you have plurals ('apples' wouldn't match '[wordboundary]apple[wordboundary]').
Hopefully this isn't more abstract than what you need but maybe good way of doing it.
I haven't tested this but I think it would work. If you can use PHP you can use str_replace to turn the spaces into keyword LIKE '%apple%'
$sentence = "John liked to eat apples";
$sqlversion = str_replace(" ","%' OR Keyword like '%",$sentence );
$finalsql = "%".$sqlversion."%";
the above will echo:
%John%' OR Keyword like '%liked%' OR Keyword like '%to%' OR Keyword like '%eat%' OR Keyword like '%apples%
Then just combine with your SQl statement
SQL ="SELECT *
FROM keywords_table
WHERE Keyword like" . $finalsql;
Storing comma delimited data is... less than ideal.
If you broke up the string "John liked to eat apples" into individual words, you could use the FIND_IN_SET operator:
WHERE FIND_IN_SET('apple', t.keywords) > 0
The performance wouldn't be great - this operation is better suited to Full Text Search.
I'm not aware of any direct solution to that type of query. But Full Text Search is a possibility. If you have a full-text index on the field of interest then a search with OR between each word in the sentence (although I think the OR operator is implied) would find that record ... but it might also find more than you want too.
I really don't think what you are looking for is completely possible but you can look into Full Text Search or SOUNDEX. SOUNDEX, for example, can do something like:
WHERE SOUNDEX(sentence) = SOUNDEX('%'+keywords+'%');
I have never tried it in this context but you should and let me know how it works out.