I have the following problem with a MySQL query in C#:
Given a list of strings, I want to query the database for any rows that match said strings. The strings are unique in that each string matches no more than one row. Today, my query looks something like this:
SELECT Id FROM SomeTable
WHERE SomeColumn IN("foo", "bar", "baz")
Now, ideally I would like to be able to map the result from the query directly to the list of strings I supplied in the IN clause:
String Returned ID
------------------------------------------
foo 123
bar NULL <-- Missing row filled with NULL
baz 42
This works fine as long as all strings I pass to the query match a row. When one is missing, however, I would like to fill in the blank with a NULL as in the example above.
Is there any way to accomplish this?
Edit: I should probably have pointed out that the solution must scale to a lot of strings. The way I do it right now is that I pass 100 at a time through the IN clause.
You could do this:
SELECT
helper.SomeColumn,
SomeTable.Id
FROM
(
SELECT 'foo' AS SomeColumn
UNION SELECT 'bar'
UNION SELECT 'baz'
) AS helper
LEFT JOIN SomeTable ON SomeTable.SomeColumn = helper.SomeColumn
Of course you can create the helper table (as a temp table) beforehand instead of inline.
Anyway, maybe it is smarter and more efficient to just do the query you have (WHERE SomeColumn IN (...)) and simply figure out the missing rows in your application. You will loop over them anyway, so you will notice.
What you could do is SELECT the set of strings as a result set and then LEFT JOIN on SomeTable.SomeColumn.
Try this:
SELECT Id
FROM (
SELECT "foo" SomeColumn
UNION ALL
SELECT "bar" AS SomeColumn
UNION ALL
SELECT "baz" AS SomeColumn
) b
LEFT JOIN
SomeTable a
ON a.SomeColumn = b.SomeColumn
Related
(MySQL)
I have a query to check if 'phone_number' or 'fax_number' startsWith a value from a given array,
lets say const possibleValues = [123,432,645,234]
currently my query runs with the 'or' condition, to check if -
'phone_number' or 'fax_number' that starts with 123
or
'phone_number' or 'fax_number' that starts with 432
or
'phone_number' or 'fax_number' that starts with 645
or
'phone_number' or 'fax_number' that starts with 234
it runs extremely slow on a big database, and I wish to make it faster,
is there a way to make it run faster?
I'm kinda new to sql queries,
any help would be highly appreciated!
You can try something like:
SELECT * FROM table_1
WHERE CONCAT(',', `phone_number`, ',') REGEXP ',(123|432|645|234),'
OR CONCAT(',', `fax_number`, ',') REGEXP ',(123|432|645|234),';
Demo
Try creating an in-line table and join with it.
WITH telnostart(telnostart) AS (
SELECT '123'
UNION ALL SELECT '432'
UNION ALL SELECT '645'
UNION ALL SELECT '234'
)
SELECT
*
FROM your_search_table
JOIN telnostart ON (
LEFT(tel_number,3) = telnostart
OR LEFT(fax_number,3) = telnostart
you can use a case statement to add a flag column
select *
,case when left(phone_number,3) in (123,432,645,234) or left(fax_number,3) in (123,432,645,234) then 1 else 0 end as contact_check_flag
from table_name
As per your requirement, you can filter it or use it elsewhere.
SELECT * FROM table_1
WHERE `phone_number` REGEXP '^(123|432|645|234)'
OR `fax_number` REGEXP '^(123|432|645|234)';
But it won't be fast. (And no regular INDEX will help.)
If there phone numbers are spelled out like in the US: "123-456-7890", then you could use a FULLTEXT(phone_number, fax_number) index and
SELECT * FROM table_1
WHERE MATCH(phone_number, fax_number)
AGAINST('123 432 645 234');
This is likely to be much faster, but not as "general".
I am trying to optimize the search engine of my wensite. My data base contains phrases. #word is defined as varchar and contains a similar phrase to the one which exist in the DB.
I want if the given search phrase matches exactly to the entry in DB the entry will be chosen, if nothing could be found, search with like '%phrase%' and if nothing will be find with this method, then the MATCH columnx against (phrase) method should be used. This is the code I tried with:
select distinct columnx
from tabley
where
( CASE when columnx LIKE #word is not null
then columnx LIKE #word
when columnx like concat('%',#word,'%') is not null
then columnx like concat('%',#word,'%')
else MATCH (columnx) AGAINST (#word) END
);
To make sure if the cases on a standalone select query works fine I used them separately in where clause. I get result for these queries:
select distinct columnx from view_materialisiert where MATCH (columnx) AGAINST (#word);
and
select distinct columnx from view_materialisiert where columnx like concat('%',#word,'%');
And as expected no result for:
select distinct columnx from view_materialisiert where columnx like #word;
The question is why i dont get any result when I use the case condition at all?
If you want values that match on any of the three condition, you can use boolean logic:
select columnx
from tabley
where columnx = #word
or columnx like concat('%', #word, '%')
or match(columnx) against (#word)
Or you can extend the case logic:
where case
when columnx = #word then 1
when columnx like concat('%', #word, '%') then 1
when match(columnx) against (#word) then 1
end
However I am unsure that's really what you expect. It seems like you want to iteratively check the conditions, trying the next one only when the preceding had no match on the entire table. This type of logic would be typically implemented with union all and not exists:
select columnx
from tabley
where columnx = #word
union all
select columnx
from tabley
where columnx like concat('%', #word, '%')
and not exists (select 1 from tabley where columnx = #word)
union all
select columnx
from tabley
where match(columnx) against (#word)
and not exists (select 1 from tabley where columnx = #word)
and not exists (select 1 from tabley where columnx like concat('%', #word, '%'))
How the database will optimize such query is highly dependent on your data and other factors. In the best case scenario, the following members will be "skipped" as soon as one member returns anything (because the not exists subquery is quite explicit about that), but there is no guarantee. You would need to assess the performance on your actual dataset.
Do only
MATCH (columnx) AGAINST ("+word" IN BOOLEAN MODE)
It is very fast. That expression eliminates the need for the exact match and some of the other cases.
The OR approaches mentioned are quite inefficient. They will check every row, usually with every test.
Caveats:
"Short" words cannot be used.
"Stop" words cannot be used.
If you aren't careful about those limitations, you will get nothing or everything. So do some preprocessing to decide when MATCH will work.
I tried something out. Here is a simple example in SQL Fiddle: Example
There is a column someNumbers (comma-seperated numbers) and I tried to get all the rows where this column contains a specific number. Problem is, the result only contains rows where someNumbers starts with the specific number.
The query SELECT * FROM myTable where 2 in ( someNumbers ) only returns the row with id 2 and not the row with id 1.
Any suggestions? Thank you all.
You are storing data in the wrong format! You should not be storing multiple values in a single string column. You should not be storing numbers as strings. Instead, you should have a junction table with one row per id and per number.
Sometimes, you just have no choice, because someone else created a really poorly designed database. For these situations, MySQL has the function find_in_set():
SELECT *
FROM myTable
WHERE find_in_set(2, someNumbers ) > 0;
The right solution, however, is to fix the data model.
While Gordon's answer is a good one, here is a way to do this with like
SELECT * FROM myTable where someNumbers like '2,%' or someNumbers like '%,2,%' or someNumbers like '%,2'
The first like checks if your array starts with the number you are looking for (2). The second one checks if 2 is within the array and the last like tests for appearance at the end.
Note that the commas are essential here, because something like '%2%' would also match ...,123,...
EDIT: As suggested by the OP it may happen that only a single value is present in the row. Consequently, the query must check this case by doing ... someNumbers = '2'
I would suggest this query :
SELECT * FROM myTable where someNumbers like '%2%'
It will select every entry where someNumbers contains '2'
Select * from table_name where coloumn_name IN(value,value,value)
you can use it
I am looking to compare the results of 2 cells in the same row. the way the data is structured is essentially this:
Col_A: table,row,cell
Col_B: row
What I want to do is compare when Col_A 'row' is the same as Col_B 'row'
SELECT COUNT(*) FROM MyTable WHERE Col_A CONTAINS Col_B;
sample data:
Col_A: a=befd-47a8021a6522,b=7750195008,c=prof
Col_B: b=7750195008
Col_A: a=bokl-e5ac10085202,b=4478542348,c=pedf
Col_B: b=7750195008
I am looking to return the number of times the comparison between Col_A 'b' and Col_B 'b' is true.
This does what I was looking for:
SELECT COUNT(*) FROM MyTable WHERE Col_A LIKE CONCAT('%',Col_B,'%');
I see You answered Your own question.
SELECT COUNT(*) FROM MyTable WHERE Col_A LIKE CONCAT('%',Col_B,'%');
is good from performance perspective. While normalization is very good idea, it would not improve speed much in this particular case. We must simply scan all strings from table. Question is, if the query is always correct. It accepts for example
Col_A: a=befd-47a8021a6522,ab=7750195008,c=prof
Col_B: b=7750195008
or
Col_A: a=befd-47a8021a6522,b=775019500877777777,c=prof
Col_B: b=7750195008
this may be a problem depending on the data format. Solution is quite simple
SELECT COUNT(*) FROM MyTable WHERE CONCAT(',',Col_A,',') LIKE CONCAT('%,',Col_B,',%');
But this is not the end. String in LIKE is interpreted and if You can have things like % in You data You have a problem. This should work on mysql:
SELECT COUNT(*) FROM MyTable WHERE LOCATE(CONCAT(',',Col_B,','), CONCAT(',',Col_A,','))>0;
SELECT * FROM MyTable WHERE Col_A = Col_B (AND Col_A = 'cell')
^^ Maybe you are looking for this statement. The part in brackets is optional.
If this is not the solution, please supply us with further information.
The easiest way would be to use the IN operator.
SELECT COUNT(*) FROM MyTable WHERE Col_A IN (Col_B);
More info on the IN operator: http://www.w3schools.com/sql/sql_in.asp
There's also the SUBSTRING() or MID() (depending on what you're using) function if you know that the substring will be in the same position everytime.
MID()/SUBSTRING() function: http://www.w3schools.com/sql/sql_func_mid.asp
You can use SUBSTRING_INDEX to extract a delimited field from a column.
SELECT COUNT(*)
FROM MyTable
WHERE Col_B = SUBSTRING_INDEX(SUBSTRING_INDEX(Col_A, ',', 2), ',', -1)
You need to call it twice to get a single field. The inner call gets the first two fields, the outer call gets the last field of that.
Note that this will be very slow if the table is large, because it's not possible to index substrings in MySQL. It would be much better if you normalized your schema so each field is in a separate column.
If column Col_a has data with format table,row,cell then search expression will be next:
SELECT COUNT(*) FROM MyTable AS MT
WHERE SUBSTRING(Col_A,
INSTR(Col_A, ',b=') + 3,
INSTR(Col_A, ',c=') - INSTR(Col_A, ',b=') + 3) = Col_B
I'm trying do something like this:
SELECT * FROM table WHERE column IN (1,2,3)
but in place of 1,2,3 I want to use a column from another table that contains a comma-delimited list just like "1,2,3" above.
I have tried to do this:
SELECT
GROUP_CONCAT(a.eating_area SEPARATOR ', ')
FROM table_areas a
WHERE a.eating_area_id IN (
SELECT
o.eating_area_ids
FROM table_offers o WHERE o.rid=1
)
however this only returns the value associated with 1, and not 2 or 3. Can this be done or is there another way to do this?
Many thanks
SELECT * FROM table t
WHERE IF(FIND_IN_SET(column,(SELECT "1,2,3" FROM otherTable WHERE 1))>=1,1,0)
-- FIND_IN_SET will return the position.
I don't know if it's the best way to do it but... i think it could work.
Source: Find_in_set