Good people,
I would like to know what approach they would take to make a union only if the above query, from the union, returns values. Consider that the tables are compatible EX:
SELECT * FROM Tabela1
UNION
SELECT * FROM Tabela2
/*Esta query so deve ser executada apenas se a query acima, select * from Tabela1, tiver devolvido algum valor*/
Regards, Leandro
Only if you use the table above to filter the second
declare @Tabela1 table
(
id int
)
declare @Tabela2 table
(
id int
)
--insert into @Tabela1 values (1),(2),(3),(4)
insert into @Tabela2 values (1),(2),(3),(5)
SELECT * FROM @Tabela1
UNION
SELECT * FROM @Tabela2
where exists (SELECT top 1 id FROM @Tabela1)
I tested the statement below and it worked (I think it's easy to understand):
select * from bairro where id = 1
union
select * from bairro where id > 15 and
EXISTS (select FIRST 1 * from bairro where id = 1)
SELECT
*
FROM(
SELECT * FROM Tabela1
UNION ALL
SELECT * from Tabela2) as aux
WHERE (SELECT COUNT(*) FROM Tabela1) > 0