使用
exists()让所有的客户和标签，当客户有指数1的标签：
select ct.customernumber, ct.tagindex, c.datefrom customers c inner join customers_tags ct on c.customernumber = ct.customernumberwhere exists ( select 1 from customers_tags i where i.customernumber = ct.customernumber and i.tagindex = 1 )
或使用
in()：
select ct.customernumber, ct.tagindex, c.datefrom customers c inner join customers_tags ct on c.customernumber = ct.customernumberwhere c.customernumber in ( select i.customernumber from customers_tags i where i.tagindex = 1 )
