text: -- join5.test
  -- 
  -- execsql {
  --     CREATE TABLE ab(a,b);
  --     INSERT INTO "ab" VALUES(1,2);
  --     INSERT INTO "ab" VALUES(3,NULL);
  -- 
  --     CREATE TABLE xy(x,y);
  --     INSERT INTO "xy" VALUES(2,3);
  --     INSERT INTO "xy" VALUES(NULL,1);
  -- }
  CREATE TABLE ab(a,b);
  INSERT INTO "ab" VALUES(1,2);
  INSERT INTO "ab" VALUES(3,NULL);
  CREATE TABLE xy(x,y);
  INSERT INTO "xy" VALUES(2,3);
  INSERT INTO "xy" VALUES(NULL,1);