PARAMETERS p Short;
SELECT First(Choose(p,t1.a,t2.a,t3.a)) AS a, First(Choose(p,t1.b,t2.b,t3.b)) AS b
FROM t1, t2, t3
GROUP BY Choose(p,t1.cou,t2.cou,t3.cou);

SELECT First(t1.a) AS a, First(t1.b) AS b
FROM t1, t2, t3
GROUP BY t1.cou;

PARAMETERS p Short;
SELECT First(Choose(p,t1.a,t2.a,t3.a)) AS a, First(Choose(p,t1.b,t2.b,t3.b)) AS b
FROM
[select * from t1 union select * from OneLine]. AS t1,
[select * from t2 union select * from OneLine]. AS t2,
[select * from t3 union select * from OneLine]. AS t3
GROUP BY Choose(p,t1.cou,t2.cou,t3.cou)
HAVING Choose(p,t1.cou,t2.cou,t3.cou) Not In (select cou from OneLine);

select *,  1  as t from t1
union
select *,  2  as t from t2
union
select *,  3  as t from t3;

PARAMETERS p Short;
select * from U where t=p

PARAMETERS p Text;
SELECT * FROM [
select *,  "t1"  as t from t1
union
select *,  "t2"  as t from t2
union
select *,  "t3"  as t from t3
]. AS U
WHERE t=p;