Illuminate\Database\Query\Builder::select PHP Method

    public function select($columns = ['*'])
    {
        $this->columns = is_array($columns) ? $columns : func_get_args();
        return $this;
    }

 /**
  * Add subselect queries to count the relations.
  *
  * @param  mixed  $relations
  * @return $this
  */
 public function withCount($relations)
 {
     if (is_null($this->query->columns)) {
         $this->query->select(['*']);
     }
     $relations = is_array($relations) ? $relations : func_get_args();
     foreach ($this->parseWithRelations($relations) as $name => $constraints) {
         // First we will determine if the name has been aliased using an "as" clause on the name
         // and if it has we will extract the actual relationship name and the desired name of
         // the resulting column. This allows multiple counts on the same relationship name.
         $segments = explode(' ', $name);
         if (count($segments) == 3 && Str::lower($segments[1]) == 'as') {
             list($name, $alias) = [$segments[0], $segments[2]];
         }
         $relation = $this->getHasRelationQuery($name);
         // Here we will get the relationship count query and prepare to add it to the main query
         // as a sub-select. First, we'll get the "has" query and use that to get the relation
         // count query. We will normalize the relation name then append _count as the name.
         $query = $relation->getRelationCountQuery($relation->getRelated()->newQuery(), $this);
         $query->callScope($constraints);
         $query->mergeModelDefinedRelationConstraints($relation->getQuery());
         // Finally we will add the proper result column alias to the query and run the subselect
         // statement against the query builder. Then we will return the builder instance back
         // to the developer for further constraint chaining that needs to take place on it.
         $column = snake_case(isset($alias) ? $alias : $name) . '_count';
         $this->selectSub($query->toBase(), $column);
     }
     return $this;
 }