Module: ArJdbc::MSSQL::LimitHelpers::SqlServerReplaceLimitOffset

Included in:
Arel::Visitors::SQLServer
Defined in:
lib/arjdbc/mssql/limit_helpers.rb

Class Method Summary collapse

Class Method Details

.replace_limit_offset!(sql, limit, offset, order) ⇒ Object 



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# File 'lib/arjdbc/mssql/limit_helpers.rb', line 13

def replace_limit_offset!(sql, limit, offset, order)
  if limit
    offset ||= 0
    start_row, end_row = offset + 1, offset + limit.to_i

    if match = FIND_SELECT.match(sql)
      select, distinct, rest_of_query = match[1], match[2], match[3]
      rest_of_query.strip!
    end
    rest_of_query[0] = '*' if rest_of_query[0...1] == '1' && rest_of_query !~ /1 AS/i
    if rest_of_query[0...1] == '*'
      from_table = Utils.get_table_name(rest_of_query, true)
      rest_of_query = "#{from_table}.#{rest_of_query}"
    end

    # Ensure correct queries if the rest_of_query contains a 'GROUP BY'. Otherwise the following error occurs:
    #   ActiveRecord::StatementInvalid: ActiveRecord::JDBCError: Column 'users.id' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.
    #   SELECT t.* FROM ( SELECT ROW_NUMBER() OVER(ORDER BY users.id) AS _row_num, [users].[lft], COUNT([users].[lft]) FROM [users] GROUP BY [users].[lft] HAVING COUNT([users].[lft]) > 1 ) AS t WHERE t._row_num BETWEEN 1 AND 1
    if rest_of_query.downcase.include?('group by')
      if order.match(/^ORDER +BY +(#{FIND_AGGREGATE_FUNCTIONS})\(/i)
        # do nothing
      elsif order.count(',') == 0
        order.gsub!(/ORDER +BY +([^\s]+)(\s+ASC|\s+DESC)?/i, 'ORDER BY MIN(\1)\2')
      else
        raise('Only one order condition allowed.')
      end
    end

    if distinct # select =~ /DISTINCT/i
      order = order.gsub(/([a-z0-9_])+\./, 't.')
      new_sql = "SELECT t.* FROM "
      new_sql << "( SELECT ROW_NUMBER() OVER(#{order}) AS _row_num, t.* FROM (#{select} #{rest_of_query}) AS t ) AS t"
      new_sql << " WHERE t._row_num BETWEEN #{start_row} AND #{end_row}"
    else
      select_columns_before_from = rest_of_query.gsub(/FROM.*/, '').strip
      only_one_column            = !select_columns_before_from.include?(',')
      only_one_id_column         = only_one_column && (select_columns_before_from.ends_with?('.id') || select_columns_before_from.ends_with?('.[id]'))

      if only_one_id_column
        # If there's only one id column a subquery will be created which only contains this column
        new_sql = "#{select} t.id FROM "
      else
        # All selected columns are used
        new_sql = "#{select} t.* FROM "
      end
      new_sql << "( SELECT ROW_NUMBER() OVER(#{order}) AS _row_num, #{rest_of_query} ) AS t"
      new_sql << " WHERE t._row_num BETWEEN #{start_row} AND #{end_row}"
    end

    sql.replace(new_sql)
  end
  sql
end