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

.append_limit_row_num_clause(sql, limit, offset) ⇒ Object 



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# File 'lib/arjdbc/mssql/limit_helpers.rb', line 65

def append_limit_row_num_clause(sql, limit, offset)
  if limit
    start_row = offset + 1; end_row = offset + limit.to_i
    sql << " WHERE t._row_num BETWEEN #{start_row} AND #{end_row}"
  else
    sql << " WHERE t._row_num > #{offset}"
  end
end

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



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# File 'lib/arjdbc/mssql/limit_helpers.rb', line 14

def replace_limit_offset!(sql, limit, offset, order)
  offset ||= 0

  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')
    order_start = order.strip[0, 8]; order_start.upcase!
    if order_start == 'ORDER BY' && order.match(FIND_AGGREGATE_FUNCTION)
      # 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"
    append_limit_row_num_clause(new_sql, limit, offset)
  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"
    append_limit_row_num_clause(new_sql, limit, offset)
  end

  sql.replace new_sql
end