我怎样才能让 JooQ 联合两个不同的表，它们具有相同的列和数据类型？

Question

I have two tables in my database, these tables have the same exact columns and datatypes but in different order.

Table A has the columns: A, B, C, D.

Table B has the columns: A, C, D, B.

I have an application that uses JooQ to query the database, and that it utilized the Codegen to create the Tables and Records. However, it will not allow me to union my two select statements due to a compile error. What can I do, to union the two tables?

StepWhereSelect<ARecord> query = dsl.selectFrom(A);
StepWhereSelect<BRecord> query2 = dsl.selectFrom(B);
query.union(query2)

On the variable inside the union function, it compains about a type mismatch from SelectUnionStep about union(ARecord) cannot be applied to union(BRecord).

Where can I do in JooQ to union these 2 tables?

Answer 1

What you're looking for is jOOQ support for the SQL standard syntax UNION CORRESPONDING . The syntax is currently not implemented in any RDBMS I'm aware of, but it could be emulated by jOOQ, easily. In the absence of this syntax support, you can create the correct order of columns in both subqueries using this code:

var q1 = dsl.select(Stream.of(A.fields()).sorted(Field::getName).collect(toList()))
            .from(A);
var q2 = dsl.select(Stream.of(B.fields()).sorted(Field::getName).collect(toList()))
            .from(A);
q1.union(q2).fetch();

Of course, there is no type safety in this anymore. If you still want to receive ARecord types, you can write

q1.union(q2).fetchInto(A);