Forum: Ruby on Rails conditional count mysql query.

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Morgan M. (Guest)
on 2009-04-06 03:10
so i have a database filled with stats and i need to return a number
from those stats for processing.  how would i go about counting how many
of a certian thing there are in a particular column..

example: say i wanted to see how many records showed female in the users
table but i didn't actually want to pull a bunch of info, i just want
the number returned.

thanks..  i hope this makes sense.
Simon M. (Guest)
on 2009-04-06 03:18
(Received via mailing list)
isn't it just
User.count(:conditions => {:sex => 'female'})
syntax may be a bit wrong, but you should be able to google to sort it
out.

Simon
Matthew MacLeod (Guest)
on 2009-04-06 03:18
(Received via mailing list)
On 6 Apr 2009, at 00:10, Morgan M. wrote:
> example: say i wanted to see how many records showed female in the
> users
> table but i didn't actually want to pull a bunch of info, i just want
> the number returned.

Use the count method: Person.count("gender", :conditions=>["gender=?",
"female"])

There are more calculation methods available in the ActiveRecord
Calculations model if you check the documentation.

-Matt
Schalk N. (Guest)
on 2009-04-06 03:19
(Received via mailing list)
Hi there Morgan,

Something such as the following should do the trick:
Article.count(:conditions => "status = 'active'")

HTH,
Schalk
QJGui (Guest)
on 2009-04-07 08:24
(Received via mailing list)
Count operates using three different approaches.

    * Count all: By not passing any parameters to count, it will
return a count of all the rows for the model.
    * Count using column: By passing a column name to count, it will
return a count of all the rows for the model with supplied column
present
    * Count using options will find the row count matched by the
options used.

The third approach, count using options, accepts an option hash as the
only parameter. The options are:

    * :conditions: An SQL fragment like "administrator = 1" or
[ "user_name = ?", username ]. See conditions in the intro to
ActiveRecord::Base.
    * :joins: Either an SQL fragment for additional joins like "LEFT
JOIN comments ON comments.post_id = id" (rarely needed) or named
associations in the same form used for the :include option, which will
perform an INNER JOIN on the associated table(s). If the value is a
string, then the records will be returned read-only since they will
have attributes that do not correspond to the table‘s columns.
Pass :readonly => false to override.
    * :include: Named associations that should be loaded alongside
using LEFT OUTER JOINs. The symbols named refer to already defined
associations. When using named associations, count returns the number
of DISTINCT items for the model you‘re counting. See eager loading
under Associations.
    * :order: An SQL fragment like "created_at DESC, name" (really
only used with GROUP BY calculations).
    * :group: An attribute name by which the result should be grouped.
Uses the GROUP BY SQL-clause.
    * :select: By default, this is * as in SELECT * FROM, but can be
changed if you, for example, want to do a join but not include the
joined columns.
    * :distinct: Set this to true to make this a distinct calculation,
such as SELECT COUNT(DISTINCT posts.id) …
    * :from - By default, this is the table name of the class, but can
be changed to an alternate table name (or even the name of a database
view).

Examples for counting all:

  Person.count         # returns the total count of all people

Examples for counting by column:

  Person.count(:age)  # returns the total count of all people whose
age is present in database

Examples for count with options:

  Person.count(:conditions => "age > 26")
  Person.count(:conditions => "age > 26 AND job.salary >
60000", :include => :job) # because of the named association, it finds
the DISTINCT count using LEFT OUTER JOIN.
  Person.count(:conditions => "age > 26 AND job.salary >
60000", :joins => "LEFT JOIN jobs on jobs.person_id = person.id") #
finds the number of rows matching the conditions and joins.
  Person.count('id', :conditions => "age > 26") # Performs a COUNT(id)
  Person.count(:all, :conditions => "age > 26") # Performs a COUNT(*)
(:all is an alias for '*')

Note: Person.count(:all) will not work because it will use :all as the
condition. Use Person.count instead.


On Apr 6, 7:10 am, Morgan M. <removed_email_address@domain.invalid>
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