I am using Model.group(:category) in order to get unique records based on category field in Rails 5 application.
Table data:
id catgeory description
1 abc test
2 abc test1
3 abc test2
4 xyz test
5 xyz testabc
I want records (1,4) as a result. Therefore I am using Model.group(:category) which works fine for MYSQL whose sql_mode is " " .
Unforunately its throwing an error "SELECT list is not in GROUP BY clause and contains nonaggregated column which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by" whose sql_mode is "only_full_group_by".
whats the best way to change the query to match the mode?
Perhaps try specifying which id you want? You could use MIN(id), MAX(id) etc.
MySQL supports a non-standard extension to SQL described here. To continue using that behavior, you could change the sql_mode to TRADITIONAL in config/database.yml.
Related
I'm using a QUERY function in Google Sheets. I have a named data range ("Contributions" in table on another sheet) that consists of many columns, but I'm only concerned with two of them. For simplicity sake, it looks something like this:
I have another table that contains the unique set of names (e.g.: "Fred", "Ginger", etc. each only once) and I want to extract the level # (column B) from the above table to insert the most recent (largest number) in this second table.
Right now, my query looks like this:
=QUERY(Contributions, "select B,C where C='"&A5&"' order by B desc limit 1",1)
The problem is, that it outputs both B & C data - e.g.:
11 Fred
But since I already have the name (in column A of this other table) I only want it to output the value from B - e.g.:
11
Is there a way to output only a subset (in this case 1 of 2) of the columns of output based on a directive within the query itself (as opposed to doing post-processing of the results)?
Outputting a Subset of Columns Used in Query
In order to output only certain columns of a query result, the query only needs to select the columns to be displayed while the constraints / conditions may utilize other columns of data.
For example (as an answer to my own question) - I have a table like this:
I needed to get the data from the row with a name matching another cell (on another sheet) and with the latest (largest) number - but I only want to output the number part.
My initial attempt was:
=QUERY(Contributions, "select B,C where C='"&A5&"' order by B desc limit 1",1)
But that output both B & C where I only wanted B. The answer (thanks to # Calculuswhiz) was to continue using C for the condition but only select on B:
=QUERY(Contributions, "select B where C='"&A5&"' order by B desc limit 1",1)
This ActiveRecord query works in SQLite:
SlotReq.group(:team_id)
In PostgreSQL, the same query gives this error "GroupingError - column slot_reqs.id must appear in the GROUP BY clause or be used in an aggregate function"
Based on the answer to this question I changed my query to:
SlotReq.select("slot_reqs.team_id").group("slot_reqs.team_id")
and it works as expected.
I would like to know if I'm doing it right and why does this work?
Yes, you are doing it right, although you could also use:
SlotReq.select(:team_id).group(:team_id)
What happens is that PG (among other DB's) needs that all column names in SELECT must be either aggregated or used in GROUP BY clause; this is because, if any unagreggated column is omitted, it could lead to indeterminate behavior (i.e. What value should be used in that column?)
So, by specifying in select just the column you want to group, you don't omit any column; on the other hand, using group withoutselect, is equivalent to doing SELECT * FROM table GROUP BY column, which brings all columns but only one being specified on GROUP BY clause.
I'm having a problem with a .first query in Rails 4 ActiveRecord. New behavior in Rails 4 is to add an order by the id field so that all db systems will output the same order.
So this...
Foo.where(bar: baz).first
Will give the query...
select foos.* from foos order by foos.id asc limit 1
The problem I am having is my select contains two sum fields. With the order by id thrown in the query automatically, I'm getting an error that the id field must appear in the group by clause. The error is right, no need for the id field if I want the output to be the sum of these two fields.
Here is an example that is not working...
baz = Foo.find(77).fooviews.select("sum(number_of_foos) as total_number_of_foos, sum(number_of_bars) as total_number_of_bars").reorder('').first
Here is the error...
ActiveRecord::StatementInvalid: PG::GroupingError: ERROR: column "foos.id" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: ...bars FROM "fooviews" ORDER BY "...
Since the select is an aggregate expression, there is no need for the order by id, but AR is throwing it in automatically.
I found that I can add a reorder('') on to the end before the .first and that removes the order by id, but is that the right way to fix this?
Thank you
[UPDATE] What I neglected to mention is that I'm converting a large Rails 3 project to Rails 4. So the output from the Rails 3 is an AR object. If possible, the I would like the solution to keep in that format so that there is less code to change in the conversion.
You will want to use take:
The take method retrieves a record without any implicit ordering.
For example:
baz = Foo.find(77).fooviews.select("sum(number_of_foos) as total_number_of_foos, sum(number_of_bars) as total_number_of_bars").take
The commit message here indicates that this was a replacement for the old first behavior.
I am getting this error in the pg production mode, but its working fine in sqlite3 development mode.
ActiveRecord::StatementInvalid in ManagementController#index
PG::Error: ERROR: column "estates.id" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: SELECT "estates".* FROM "estates" WHERE "estates"."Mgmt" = ...
^
: SELECT "estates".* FROM "estates" WHERE "estates"."Mgmt" = 'Mazzey' GROUP BY user_id
#myestate = Estate.where(:Mgmt => current_user.Company).group(:user_id).all
If user_id is the PRIMARY KEY then you need to upgrade PostgreSQL; newer versions will correctly handle grouping by the primary key.
If user_id is neither unique nor the primary key for the 'estates' relation in question, then this query doesn't make much sense, since PostgreSQL has no way to know which value to return for each column of estates where multiple rows share the same user_id. You must use an aggregate function that expresses what you want, like min, max, avg, string_agg, array_agg, etc or add the column(s) of interest to the GROUP BY.
Alternately you can rephrase the query to use DISTINCT ON and an ORDER BY if you really do want to pick a somewhat arbitrary row, though I really doubt it's possible to express that via ActiveRecord.
Some databases - including SQLite and MySQL - will just pick an arbitrary row. This is considered incorrect and unsafe by the PostgreSQL team, so PostgreSQL follows the SQL standard and considers such queries to be errors.
If you have:
col1 col2
fred 42
bob 9
fred 44
fred 99
and you do:
SELECT col1, col2 FROM mytable GROUP BY col1;
then it's obvious that you should get the row:
bob 9
but what about the result for fred? There is no single correct answer to pick, so the database will refuse to execute such unsafe queries. If you wanted the greatest col2 for any col1 you'd use the max aggregate:
SELECT col1, max(col2) AS max_col2 FROM mytable GROUP BY col1;
I recently moved from MySQL to PostgreSQL and encountered the same issue. Just for reference, the best approach I've found is to use DISTINCT ON as suggested in this SO answer:
Elegant PostgreSQL Group by for Ruby on Rails / ActiveRecord
This will let you get one record for each unique value in your chosen column that matches the other query conditions:
MyModel.where(:some_col => value).select("DISTINCT ON (unique_col) *")
I prefer DISTINCT ON because I can still get all the other column values in the row. DISTINCT alone will only return the value of that specific column.
After often receiving the error myself I realised that Rails (I am using rails 4) automatically adds an 'order by id' at the end of your grouping query. This often results in the error above. So make sure you append your own .order(:group_by_column) at the end of your Rails query. Hence you will have something like this:
#problems = Problem.select('problems.username, sum(problems.weight) as weight_sum').group('problems.username').order('problems.username')
#myestate1 = Estate.where(:Mgmt => current_user.Company)
#myestate = #myestate1.select("DISTINCT(user_id)")
this is what I did.
In PostgreSQL, I created a new table and assigned a new sequence to the id column. If I insert a record from the PostgreSQL console it works but when I try to import a record from from Rails, it raises an exception that it is unable to find the associated sequence.
Here is the table:
\d+ user_messages;
Table "public.user_messages"
Column | Type | Modifiers | Storage | Description
-------------+-----------------------------+------------------------------------------------------------+----------+-------------
id | integer | not null default nextval('new_user_messages_id'::regclass) | plain |
But when I try to get the sequence with the SQL query which Rails uses, it returns NULL:
select pg_catalog.pg_get_serial_sequence('user_messages', 'id');
pg_get_serial_sequence
------------------------
(1 row)
The error being raised by Rails is:
UserMessage.import [UserMessage.new]
NoMethodError: undefined method `split' for nil:NilClass
from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:910:in `default_sequence_name'
This problem only occurs when I use the ActiveRecord extension for importing bulk records, single records get saved through ActiveRecord.
How do I fix it?
I think your problem is that you set all this up by hand rather than by using a serial column. When you use a serial column, PostgreSQL will create the sequence, set up the appropriate default value, and ensure that the sequence is owned by the table and column in question. From the fine manual:
pg_get_serial_sequence(table_name, column_name)
get name of the sequence that a serial or bigserial column uses
But you're not using serial or bigserial so pg_get_serial_sequence won't help.
You can remedy this by doing:
alter sequence new_user_messages_id owned by user_messages.id
I'm not sure if this is a complete solution and someone (hi Erwin) will probably fill in the missing bits.
You can save yourself some trouble here by using serial as the data type of your id column. That will create and hook up the sequence for you.
For example:
=> create sequence seq_test_id;
=> create table seq_test (id integer not null default nextval('seq_test_id'::regclass));
=> select pg_catalog.pg_get_serial_sequence('seq_test','id');
pg_get_serial_sequence
------------------------
(1 row)
=> alter sequence seq_test_id owned by seq_test.id;
=> select pg_catalog.pg_get_serial_sequence('seq_test','id');
pg_get_serial_sequence
------------------------
public.seq_test_id
(1 row)