I want to write an SQL query that will fetch all the students who live in a specific Post Code. Following is my query.
SELECT * FROM `students` AS ss WHERE ss.`postcode` LIKE 'SE4 1NA';
Now the issue is that in database some records are saved without the white space is postcode, like SE41NA and some may also be in lowercase, like se41na or se4 1na.
The query gives me different results based on how the record is saved. Is there any way in which I can handle this?
Using regexp is one way to do it. This performs a case insensitive match by default.
SELECT * FROM students AS ss
WHERE ss.postcode REGEXP '^SE4[[:space:]]?1NA$';
[[:space:]]? matches an optional space character.
REGEXP documentation MySQL
Whether case matters depends on the collation of the string/column/database/server. But, you can get around it by doing:
WHERE UPPER(ss.postcode) LIKE 'SE4%1NA'
The % will match any number of characters, including none. It is a bit too general for what you might really need -- but it should work fine in practice.
The more important issue is that your database does not validate the data being put into it. You should fix the application so the postal codes are correct and follow a standard format.
Use a combination of UPPER and REPLACE.
SELECT *
FROM students s
WHERE UPPER(REPLACE(s.postcode, ' ', '')) LIKE '%SE41NA%'
SELECT * FROM students AS ss
WHERE UPPER(REPLACE(ss.postcode, ' ', '')) = 'SE41NA' ;
SELECT *
FROM students AS ss
WHERE UPPER(ss.postcode) LIKE SELECT REPLACE(UPPER('SE4 1NA'), ' ', '%'); ;
I propose using the spaces replaced with the'%' placeholder. Also transform the case to upper for both sides of the LIKE operator
Related
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 need to use the '_' wildcard to find all id that are only one letter which there are a few of. However when I run my query no rows are returned.
Heres my query:
SELECT *
FROM table
WHERE id LIKE '_';
I have a table lets call Table1 that has two columns, id and name.
id either has 1 or 2 characters to label a name. I'm trying to only find the names where the id is only one character. Heres an example of the table:
id name
A Alfred
AD Andy
B Bob
BC Bridget
I only want to return Alfred and Bob in this example.
I don't want the solution but any advice or ideas would be helpful.
Here is a screenshot of my query:
http://i.imgur.com/EWTfoVI.png?1
And here is a small example of my table:
http://i.imgur.com/urGRZeK.png?1
So in this example of my table I would ideally like only East Asia... to be returned.
I if I search specifically for the character it works but for some strange reason the '_' wildcard doesn't.
For example:
SELECT *
FROM icao
WHERE prefix_code ='Z';
This works.
Try using TRIM
Select *
FROM [Table]
where TRIM(ID) LIKE '_';
In MySQL, the underscore is used to represent a wildcard for a single character. You can read more about that Pattern Matching here.
The way you have it written, your query will pull any rows where the id column is just one single character, you don't need to change anything.
Here is an SQL Fiddle example.
EDIT
One trouble shooting tip is to be sure there is no whitespace before/after the prefix code. If there is, and you need to remove it, add TRIM():
SELECT *
FROM myTable
WHERE TRIM(id) LIKE '_';
Here is an example with TRIM.
EDIT 2
A little explanation to your weird behavior, hopefully. In MySQL, if there is trailing white space on a character, it will still match if you say id = 'Z'; as seen by this fiddle now. However, leading white space will not match this, but will still be corrected by TRIM(), because that removes white space on the front and back end of the varchar.
TL;DR You have trailing white space after Z and that's causing the problem.
The most likely explanation for the behavior you observe is trailing spaces (or other whitespace) in the value. That is, you see one character
'A'
But the value may actually be stored as two (or more) characters.
'A '
To see what's actually stored, you can use the HEX and LENGTH functions.
SELECT t.foo
, LENGTH(t.foo)
, HEX(t.foo)
FROM mytable t
WHERE t.foo LIKE 'A%'
The % is a wildcard for the LIKE operator that matches any number of characters (zero, one or more).
You can use the RTRIM() function to remove trailing spaces...
SELECT RTRIM(t.foo)
, LENGTH(RTRIM(t.foo))
, HEX(RTRIM(t.foo))
FROM mytable t
WHERE t.foo LIKE 'A%'
SELECT *
FROM table
WHERE LENGTH(id)=1
Strange..., in my case works perfectly (I am using mysql 5.5).
Please, try this:
select * from mysql.help_topic where name like '_';
What set you get?
let's say I have a string in which the words are separated by 1 or more spaces and I want to use that string in and SQL LIKE condition. How do I make my SQL and tell it to match 1 or more blank space character in my string? Is there an SQL wildcard that I can use to do that?
Let me know
If you're just looking to get anything with atleast one blank / whitespace then you can do something like the following WHERE myField LIKE '% %'
If your dialect allows it, use SIMILAR TO, which allows for more flexible matching, including the normal regular expression quantifiers '?', '*' and '+', with grouping indicated by '()'
where entry SIMILAR TO 'hello +there'
will match 'hello there' with any number of spaces between the two words.
I guess in MySQL this is
where entry RLIKE 'hello +there'
I know this is late, but I never found a solution to this in relation to a LIKE question.
There is no way to do what you're wanting within a SQL LIKE. What you would have to do is use REGEXP and [[:space:]] inside your expression.
So to find one or more spaces between two words..
WHERE col REGEXP 'firstword[[:space:]]+secondword'
Another way to match for one or more space would be to use [].
It's done like this.
LIKE '%[ ]%'
This will match one or more spaces.
you can't do this using LIKE but what you can do, if you know this condition can exist in your data, is as you're inserting the data into the table, use regular expression matching to detect it up front and set a flag in a different column created for this purpose.
I just replace the whitespace chars with '%'. Lets say I want to do a LIKE query on a string like this 'I want to query this string with a LIKE'
#search_string = 'I want to query this string with a LIKE'
#search_string = ("%"+#search_string+"%").tr(" ", "%")
#my_query = MyTable.find(:all, :conditions => ['my_column LIKE ?', #search_string])
first I add the '%' to the start and end of string with
("%"+#search_string+"%")
and then replace other remaining whitespace chars with '%' like so
.tr(" ", "%")
http://www.techonthenet.com/sql/like.php
The patterns that you can choose from are:
% allows you to match any string of any length (including zero length)
_ allows you to match on a single character
I think that the question is not asking to match any spaces but to match two strings one a pattern and the other with wrong number of spaces because of typos.
In my case I have to check two fields from different tables one preloaded and the other filled typed by users so sometimes they don't respect 100% the pattern.
The solution was to use LIKE in the join
Select table1.field
from table1
left join table2 on table1.field like('%' + replace(table2.field,' ','%')+'%')
if the condition:
WHERE myField LIKE '%Hello world%'
doesn't work try
WHERE myField LIKE '%Hello%'
and
WHERE myField LIKE '%world%'
this approach is helpful in a few specific use cases, hope this helps.
I have an InnoDB database table of 12 character codes which often need to be entered by a user.
Occasionally, a user will enter the code incorrectly (for example typing a lower case L instead of a 1 etc).
I'm trying to write a query that will find similar codes to the one they have entered but using LIKE '%code%' gives me way too many results, many of which contain only one matching character.
Is there a way to perform a more detailed check?
Edit - Case sensitive not required.
Any advice appreciated.
Thanks.
Have a look at soundex. Commonly misspelled strings have the same soundex code, so you can query for:
where soundex(Code) like soundex(UserInput)
use without wildcard % for that
SELECT `code` FROM table where code LIKE 'user_input'
thi wil also check the space
SELECT 'a' = 'a ', return 1 whereas SELCET 'a' LIKE 'a ' return 0
reference
How can I search for "1-800-flowers" by "1800flowers" in MySQL?
I have the data "1-800-flowers", but I want to find it by "1800flowers".
You're probably best off creating a second column that you fill with 1800flowers (replacing all characters you want to ignore) and searching that. That way, you can make full use of indexing.
A quick way to convert all existing data would be
UPDATE table SET columnname_without_hyphens = REPLACE(columnname, "-", "");
If your problem is just ignoring hyphens, I may suggest using REPLACE to eliminate them, like this:
SELECT ... WHERE REPLACE(column, '-', '') ...
Otherwise, if you're looking for strings that "sound alike", you may want to have a look at the SOUNDEX function.
The use of the replace function will kill any ability to use an index on the column, but:
select *
from YourTable
where replace(YourColumn, '-', '') = '1800flowers'