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          // If left_field is set use it for a field-to-field condition.

          if (!empty($info['left_field'])) {

            $operator = !empty($info['operator']) ? $info['operator'] : '=';

            $left_table = (isset($info['left_table'])) ? $info['left_table'] : $left['alias'];

            $extras[] = "$join_table$info[field] $operator $left_table.$info[left_field]";

          }

          // Else if formula is set, us it for a flexible on clause.

          elseif (!empty($info['formula'])) {

            // If a field is given, we build a "$field $op $formula".

            // Without it would only be "$formula".

            $extra = '';

            if (isset($info['field'])) {

              // With a single value, the '=' operator is implicit.

              $operator = !empty($info['operator']) ? $info['operator'] : '=';

              $extra .= "$join_table$info[field] $operator ";

            $extra .= $info['formula'];

            // Add placeholder arguments.

            if (isset($info['formula_arguments']) && is_array($info['formula_arguments'])) {

              $arguments = array_merge($arguments, $info['formula_arguments']);

            $extras[] = $extra;

          // Otherwise - and if we have a value - use it for a field-to-value condition.

          elseif (!empty($info['value'])) {

            // Convert a single-valued array of values to the single-value case,

            // and transform from IN() notation to = notation

            if (is_array($info['value']) && count($info['value']) == 1) {

              if (empty($info['operator'])) {

                $operator = '=';

              }

              else {

                $operator = $info['operator'] == 'NOT IN' ? '!=' : '=';

              }

              $info['value'] = array_shift($info['value']);

            }

            if (is_array($info['value'])) {

              // With an array of values, we need multiple placeholders and the

              // 'IN' operator is implicit.

              foreach ($info['value'] as $value) {

                $placeholder_i = ':views_join_condition_' . $select_query->nextPlaceholder();

                $arguments[$placeholder_i] = $value;

              }

              $operator = !empty($info['operator']) ? $info['operator'] : 'IN';

              $placeholder = '( ' . implode(', ', array_keys($arguments)) . ' )';

            }

            else {

              // With a single value, the '=' operator is implicit.

              $operator = !empty($info['operator']) ? $info['operator'] : '=';

              $placeholder = ':views_join_condition_' . $select_query->nextPlaceholder();

              $arguments[$placeholder] = $info['value'];

            $extras[] = "$join_table$info[field] $operator $placeholder";