Multiple selection from different tables in one query - spring

Question

My question is about optimizing queries with mybatis.
List<SomeObject> someObjectList = oracleMapper.getAllSomeObject();
in my project I have to unload data from one database and make a request to another
List<String> subscriptionIds = someObjectList.stream().map(g -> g.getSubscriptionId()).collect(Collectors.toList());
List<Subscription> subscriptionsByIds = postgresMapper.getSubscriptionsByIds(subscriptionIds);
List<SubscriptionSubject> subjectsByIds = postgresMapper.getSubscriptionSubjectsByIds(subscriptionIds);
I have to do a query using a list of id to different tables twice
<select id="getSubscriptionsByIds" resultType="com.mappers.Subscription">
SELECT "s_id" as sId, "old" as old FROM "subscriptions"."subscriptions" s where s."subscription_id_old" IN
<foreach item="item" collection="subscriptionIds" separator="," open="(" close=")">
#{item}
</foreach>
</select>
<select id="getSubscriptionSubjectsByIds" resultType="com.mappers.SubscriptionSubject">
SELECT "s_id" as sId, "old" as old FROM "subscriptions"."subscription_subjects" s where s."subscription_id_old" IN
<foreach item="item" collection="subscriptionIds" separator="," open="(" close=")">
#{item}
</foreach>
</select>
#Data
public class Subscription {
private Long subscriptionId;
private String subscriptionIdOld;
//others
}
#Data
public class SubscriptionSubject {
private Long subscriptionId;
private String subscriptionIdOld;
//others
}
is it possible somehow not to do two queries, but get by with one for two tables?
There is a lot of data and there will be a lot of requests too, I would like to reduce it. thanks in advance

Answer 1

If the only difference between both queries is the table name. You can pass that value as an extra parameter and add it to the query using "SQL Injection".
For example:
<select id="getSubscriptionsByIds" resultType="com.mappers.Subscription">
SELECT "s_id" as sId, "old" as old FROM ${tableName} s
WHERE s."subscription_id_old" IN
<foreach item="item" collection="subscriptionIds" separator=","
open="(" close=")">
#{item}
</foreach>
</select>
Make sure the object you are passing as a parameter includes an extra property tableName apart from the list of IDs you are already passing.
Notice that in order to implement SQL Injection you need to use ${parameter} instead of #{parameter}. Use SQL Injection when absolutely necessary only. In the wrong hands it can open security vulnerabilities in your application.