I need to extract all records which have a field which does NOT have a unique value.
I can't figure out an elegant way to do it - using annotation or some other way. I see a "value_annotate" method to the object manager but it's unclear if it's at all related.
Currently I'm using the inelegant way of simple looping through all values and doing a get on the value, and if there's an exception it means it's not unique..
Thanks
I can't say much about the Django part, but the query would look something like:
SELECT *
FROM foo
WHERE id IN (
SELECT MAX(id)
FROM foo
GROUP BY bar
HAVING COUNT(*)=1)
This will return all records where the "bar" field is unique.
I'd go direct to a raw query in this case. This'll look something like the following, assuming you're using Django 1.2:
query = """
SELECT *
FROM table
GROUP BY field
HAVING COUNT(*) > 1
"""
non_uniques = Table.objects.raw(query)
For earlier than 1.2, see the django docs on raw queries
Related
I am trying to write code that allows me to check if there are any cases of a particular pattern inside a table.
The way I am currently doing is with something like
select count(*)
from database.table
where column like (some pattern)
and seeing if the count is greater than 0.
I am curious to see if there is any way I can speed up this process as this type of pattern finding happens in a loop in my query and all I need to know is if there is even one such case rather than the total number of cases.
Any suggestions will be appreciated.
EDIT: I am running this inside a Teradata stored procedure for the purpose of data quality validation.
Using EXISTS will be faster if you don't actually need to know how many matches there are. Something like this would work:
IF EXISTS (
SELECT *
FROM bigTbl
WHERE label LIKE '%test%'
)
SELECT 'match'
ELSE
SELECT 'no match'
This is faster because once it finds a single match it can return a result.
If you don't need the actual count, the most efficient way in Teradata will use EXISTS:
select 1
where exists
( select *
from database.table
where column like (some pattern)
)
This will return an empty result set if the pattern doesn't exist.
In terms of performance, a better approach is to:
select the result set based on your pattern;
limit the result set's size to 1.
Check whether a result was returned.
Doing this prevents the database engine from having to do a full table scan, and the query will return as soon as the first matching record is encountered.
The actual query depends on the database you're using. In MySQL, it would look something like:
SELECT id FROM database.table WHERE column LIKE '%some pattern%' LIMIT 1;
In Oracle it would look like this:
SELECT id FROM database.table WHERE column LIKE '%some pattern%' AND ROWNUM = 1;
I'm currently trying to integrate Sphinx search engine into Python application. The problem is that SphinxQL doesn't support OR clause as common SQL does. There are some hacks to use, like writing expressions in SELECT like this:
SELECT id,(field1 = val1 OR field2 = val2) as expr FROM foo_bar WHERE expr = 1;
However, it doesn't work with strings, because they should be handled using MATCH function. So I decided to divide query into separate subqueries and combine results obtained. Yet there's still a problem of getting a proper META information, especially the total_found field. Sphinx counts it for separate queries, but rows obtained from these queries may intersect and I have no ability to check it (database is large).
I believe there must be a solution. I'm using Sphinxit (SphinxAlchemy has a version conflict with SQLAlchemy I'm using).
Repost from SphinxSearch forum:
I have a table I need to search in with text and numerical columns as well. I need to
write a query with OR condition; found out that there's a way to do it using SELECT
expressions like:
SELECT *, quantity>=50 OR quantity=0 AS mycond FROM table1 WHERE mycond = 1;
Hopelessly it doesn't work with string attributes. This query isn't parsed:
SELECT *, category='foo' OR category='bar' AS mycond FROM table1 WHERE mycond = 1;
Yet this is working in Beta 2.2.3:
SELECT * FROM table1 WHERE category='foo';
What should I do to find count of rows that fit one of conditions, not every one of them?
I can make a few queries and merge obtained items into one list, but I need to now how
much of these rows are in the database now.
For attribute / facet OR'ing, I think you're correct that the only way is to put an expression in the SELECT clause.
For strings, though, check out the documentation on the fulltext query syntax. You can't exactly use the OR keyword, but something like this should work:
SELECT id, name
FROM recipes
WHERE MATCH('(#ingredients chocolate) | (#name cake)')
LIMIT 10;
I am wondering if there is a way to write the SQL so that it would return me a result as usual but now, on the first row that would return also the attribute names.
To explain what I mean:
say you have a table "test" which has 2 attributes "id" and "name":
id name
1 nik
2 tst
query:
SELECT * FROM test;
produces:
1 nik
2 tst
but what I want it to return is this:
id name
1 nik
2 tst
Is this possible?
edit: I am using PostreSQL
You cannot return the names and the actual column values in a single result unless you give up on the real datatypes (which is probably not what you want).
Your example mixes character data and numeric data in the id column and Postgres will (rightfully) refuse to return such a result set.
Edit:
I tested the "union" solution given e.g. by JNK and it fails (as expected) on Postgres, Oracle and SQL Server precisely because of the non-matching datatypes. MySQL follows it's usual habits of not throwing errors and simply converts everything to characters.
Extremely generic answer since you don't provide an RDBMS:
SELECT id, name FROM(
SELECT 'id' as 'id', 'name' as 'name', 1 as 'Rank'
UNION ALL
SELECT *, 2 as 'Rank' FROM test) as X
ORDER BY [RANK]
EDIT
Thanks to Martin for pointing out the need for the ORDER BY
Assuming you are on SQL Server, you can get the column names of a specific table by using this query:
select column_name 'Column Name', data_type 'Data Type'
from information_schema.columns
where table_name = 'putYourTableNameHere'
Then, you'll have to UNION your things together.
I agree with OMG Ponies above, the way to get this meta-data is usually from the interface you use.
for example the Perl DBI module has a method fetchrow_hashref where the columns of the returned row are returned as an associative array (hash) where the colnames are the keys.
print $ref->{'name'}; # would print nik or tst
Update:
I had forgotten to add that some of these interface layers have a method that return s the col names and you could use that instead of adding the names into your result set.
The DBI method you'd use would be $sth->{NAMES}->[0] would return the first column name.
Depending on your tools / technique, but here are a couple:
If you're using SSMS (Sql-Server), and want to copy/paste your results with the column headers:
Query Window -->
R-Click
Results -->
Grid or Text -->
Check-mark the 'Include column headers in the result set' option
If you're using Sql-Server, you can query meta-tables (sys.columns, etc.)
If you're using an ASP.NET databound control, you usually have access to methods or properties (sqldatareader.getname(i), etc.)
Anyway -- just depends on the layer you're trying to get the names from -- if these above don't help, then edit / re-tag your question so we can focus on whatever tool you're wanting to use to do this.
EDIT for PostgresSQL
If you're using PostgresSQL, you can query meta-tables (information_schema.columns, etc.)
My problem is straight forward:
I have Query A:
SELECT Old, New
FROM MAPPING
WHERE Old = [Param];
I now need a Query B that calls Query A by giving it a value for [Param].
Is that possible without VBA ?
Thanks in advance
Miloud
I don't think you can do that. But you can replace your parameter in QueryA by a reference to an unbound control. This way you can set the value of the control and queryB can silently call queryA. In the same way, you could also replace your parameter by a UDF.
It soundn like you want to create a nested select query. If you are doing a select query in B, just put it inside parentheses where [Param]; is.
It sounds as though you want to pull the results from Query A, based on data from a Query B, is that correct?
A nested query is probably your best bet. What B looks like will depend on what you want to do, but try a model similar to this:
SELECT Old, New FROM MAPPING WHERE Old
= (SELECT somefield FROM sometable WHERE somefield = somevalue);
I have a table structure like :
ID, Test_ID, Verdict, PATH, Last_Status,
Present_status, Remote_location,TestCase
I want the result to be displayed starting with TestCase
But I do not want to mention all the fileds particularly.
Is there anything like
select TestCase,* from Table order by TestCase` ?
Basically the result should be displayed as
Testcase, ID, Test_ID, Verdictm PATH,
Last_Status, Present_statusmRemote_location
If I try the above select, it does not work in MYSQL. Is there any command to achive what I require?
Thanks.
Not that I know of. Even so, it's good practice to avoid using SELECT * FROM tableName wherever possible.
If your column list ever changes, queries in your code may assign values to the wrong fields.
you have to list all the fields you want in the order you want them in. it is either use * or list what you want, and just for the future using * is bad practice.
yes, just list the columns you want first explicitly in the Select clause:
Select Testcase, t.* From TableName
But the asterisk will cause the testcase column to be output no matter what, so you will get it twice. To avoid ambiguous redundant column names, you will have to alias the first one:
Select Testcase as FirsttestCase, t.* From TableName