Is it permissible for a worshiper to join a row between two pillars in the mosque, or should he pray behind the row?

If someone enters the mosque and finds the worshippers lined up between the pillars, then standing with them in the row is more preferable than praying alone behind the row, due to the hadith: "Complete the first row, then the one after it," and "There is no prayer for one who prays alone behind the row." As for praying between the pillars, it is disliked according to the Maliki and Hanbali schools, and not disliked according to the Shafi'i and Hanafi schools.