How many times that the word pair of "barcelona" and "precolombina" occur?
Pair is a relationship of two words: w1st and w2nd, where w1st is word id of the first word and w2nd is a word id of the second word; w1st or w2nd = 'barcelona'; w1st or w2nd = 'precolombina';
SELECT SUM(occurrences) FROM biwords WHERE w1st = ( SELECT wid FROM words WHERE word = 'barcelona' ) AND w2nd = ( SELECT wid FROM words WHERE word = 'precolombina' )