#standardSQL with chars as ( SELECT * FROM UNNEST(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', null]) as char ) select str from ( select concat(ifnull(a.char, ''), ifnull(b.char, ''), ifnull(c.char, ''), ifnull(d.char, ''), ifnull(e.char, ''), ifnull(f.char, '')) as str from chars as a cross join chars as b cross