在 Java 中将多个 ResultSet 合并为单个 ResultSet
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Merging Multiple ResultSet into Single ResultSet in Java
提问by Priyank Doshi
Let say I have multiple ResultSet(each resultSet would refer to 1 row in database) (they are of same table.) . Now I want to create consolidated ResultSet which would intern have all other resultSet. So my primary goal is to create a combined ResultSet which would point to all rows which where previously pointed by individual resultSet.
假设我有多个 ResultSet（每个 resultSet 将引用数据库中的 1 行）（它们属于同一个表。）。现在我想创建合并的 ResultSet，它将实习生拥有所有其他 resultSet。所以我的主要目标是创建一个组合的 ResultSet，它将指向以前由单个 resultSet 指向的所有行。
I am using Java. Do any one know how pragmatically we can achieve this?
我正在使用 Java。有谁知道我们可以如何务实地实现这一目标？
Edit : we are using java.sql.ResultSet.
编辑：我们正在使用java.sql.ResultSet.
Edit : To make it more clear :
编辑：为了更清楚：
Let say I have
假设我有
List<ResultSet> someResults ; // each resultSet Would point to a single row in database.
I want to create a consolidated ResultSet finalResults;
我想创建一个统一的 ResultSet finalResults;
psudo code :
伪代码：
List<ResultSet> resultSets = // poppulated from code
ResultSet rs = convert(resultSets) // psude conver method
回答by Thihara
If you are talking about a java.sql.ResultSet, it's not possible as far as I know. I suggest you change your query instead.
如果您在谈论 java.sql.ResultSet，据我所知这是不可能的。我建议您改为更改查询。
Or you can retrieve the results into an java object and then combine all the objects into a Collection.
或者您可以将结果检索到一个 java 对象中，然后将所有对象组合到一个集合中。
回答by SudoRahul
If the results are gonna be from the same table, why not use UNION/UNION ALL(depending on your needs) in your query itself.
如果结果将来自同一个表，为什么不在UNION/UNION ALL查询本身中使用（取决于您的需要）。
Something like this:
像这样的东西：
select A, B
from C where Q = R
union
select A, B
from C where P = S
Or else, there is the hard way of iterating through each result set and populating POJOs and adding them to a List/Set(Based on your needs). This seems to be an overkill if there are a lot of result sets.
否则，很难遍历每个结果集并填充 POJO 并将它们添加到List/Set（根据您的需要）。如果有很多结果集，这似乎是一种矫枉过正。
回答by Evgeniy Dorofeev
I would do it this way
我会这样做
class GatheringResultSet implements ResultSet {
List<E> resultSets;
ResultSet current;
GatheringResultSet(List resultSets) {
this.resultSets = new ArrayList(resultSets);
current = resultSets.remove(0);
}
@Override
public boolean next() throws SQLException {
if (current.next()) {
return true;
}
if (resultSets.isEmpty()) {
return false;
}
current = resultSets.remove(0);
return true;
}
...
...
the rest of the methods just delegate call to current ResultSet
其余的方法只是将调用委托给当前的 ResultSet
回答by Ramkumar Pillai
public class ResultSets {
private java.util.List<java.sql.ResultSet> resultSets;
private java.sql.ResultSet current;
@lombok.SneakyThrows
public ResultSets(java.util.List<java.sql.ResultSet> resultSets) {
this.resultSets = new java.util.ArrayList<>(resultSets);
current = resultSets.remove(0);
}
@lombok.SneakyThrows
public boolean next() {
if (current.next()) {
return true;
}else if (!resultSets.isEmpty()) {
current = resultSets.remove(0);
return next();
}
return false;
}
@lombok.SneakyThrows
public int getInt(int pos){
return current.getInt(pos);
}
@lombok.SneakyThrows
public String getString(String field){
return current.getString(field);
}
}
Usage :-
用法 ：-
@lombok.SneakyThrows
public static void main(String ... args) {
Connection conn = pe.getConnection("backup");
String sql1 = "SELECT count(distinct(User_Key)) FROM user_table";
String sql2 = "SELECT count(distinct(Username)) FROM user_table";
Statement stmt1 = conn.createStatement();
Statement stmt2 = conn.createStatement();
List<ResultSet> resultSets = new ArrayList<>();
resultSets.add(stmt1.executeQuery(sql1));
resultSets.add(stmt2.executeQuery(sql2));
ResultSets rs = new ResultSets(resultSets);
while(rs.next()){
System.out.println(rs.getInt(1));
}
}
