CREATE OR REPLACE FUNCTION merge(A1 double precision[],A2 double precision[], i integer, j integer,acc double precision[])

RETURNS double precision[] AS $$

SELECT

CASE WHEN (i > array_length(A1,1) and j > array_length(A2,1)) THEN acc

WHEN i > array_length(A1,1) THEN merge(A1,A2,i,j+1,array_append(acc,A2[j]))

WHEN j > array_length(A2,1) THEN merge(A1,A2,i+1,j,array_append(acc,A1[i]))

WHEN A1[i] < A2[j] THEN merge(A1,A2,i+1,j,array_append(acc, A1[i]))

WHEN A1[i] >= A2[j] THEN merge(A1,A2,i,j+1,array_append(acc, A2[j]))

END;

$$ LANGUAGE SQL;