count(column_name = nil, options = {})
Instance Public methods
Count the records.
1 2 3 4 5 6 7 8 9 10 11 | Person.count# => the total count of all peoplePerson.count(:age)# => returns the total count of all people whose age is present in databasePerson.count(:all)# => performs a COUNT(*) (:all is an alias for '*')Person.distinct.count(:age)# => counts the number of different age values |
If count is used with group, it returns a Hash whose keys represent the aggregated column,
and the values are the respective amounts:
1 2 | Person.group(:city).count# => { 'Rome' => 5, 'Paris' => 3 } |
If count is used with select, it will count the
selected columns:
1 2 | Person.select(:age).count# => counts the number of different age values |
Note: not all valid select expressions are valid
count expressions. The specifics differ between databases. In
invalid cases, an error from the databsae is thrown.
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