java - 不使用聚合函数删除sql中的重复项

Question

我开始学习 Java，但我的练习遇到了问题。

这是整个代码的片段:

import java.io.PrintWriter;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Connection;
import java.util.ArrayList;
import java.sql.PreparedStatement;

private static final int MAX_LINES      = 44;

private static final int REPORT_COL1    = 30;   
private static final int REPORT_COL     = 15;   

private ArrayList<String>   errors      = new ArrayList<String>();
private ArrayList<String>   detailReport    = new ArrayList<String>();
private ArrayList<String>   summaryReport=  new ArrayList<String>();

String firstSortCode= (String) parameters.get("01");

if(firstSortCode==null || firstSortCode.trim().equals("")) {
    errors.add("Missing required parameter 01");
    invalidParameters= true;
}
else {
    for(int i=0; i<SORT_CODES.length; i++) {
        if(firstSortCode.equals(SORT_CODES[i][0])) {
            pSort1              = SORT_CODES[i][1];
            sort1Attr           = SORT_CODES[i][2];
            sort1GetDescTable   = SORT_CODES[i][3];
            sort1GetDescCode    = SORT_CODES[i][4];
            sort1GetDescValue   = SORT_CODES[i][5];
            val1 = firstSortCode + " - " + pSort1;
            break;
        }
    }
    if(pSort1.equals("")) {
        errors.add("Invalid value '"+ firstSortCode + "' for parameter 01");
        invalidParameters= true;
    }
}

String mainSelectSQL ="SELECT shrdgmr_pidm, " +  
"   shrdgmr_levl_code, "+   
"   shrdgmr_grst_code, " 
"  NVL("+sort1Attr+", 'Not Reported') ";


mainSelectSQL =mainSelectSQL +
    "FROM shrdgmr " + 
    "WHERE shrdgmr_pidm is not null " + 

//Appends the ORDER BY clause
mainSelectSQL+= "ORDER BY "+sort1Attr;


//Executes the query and obtains the ResultSet
ResultSet rs= sqlStatement.executeQuery();

String sort1Desc= "***";            
String Sort1Prev= "*";

//Arrays to hold the student counts for each of the reported sort values
int sort1Count= 0;

int grandTotal = 0;

while(rs.next()) {
    String Value1       = rs.getString(2);  

    if(!Value1.equals(prevSort1Value)) {


    String sort1Record= Library.lPad(sort1Count, REPORT_COL, ' ');

    if(!sort1Desc.equals("***")) {

        if(lineCount[0]+4>MAX_LINES) {
            startNewPage(detailReport, pageCount, lineCount, currentDate, 
                databaseName, pGradTerm, pInitiator, sort1Desc, pSort1, false);
        }

            detailReport.add(Library.rPad(sort1Desc, REPORT_COL1, ' ')+sort1Record);
            summaryReport.add(Library.rPad(sort1Desc, REPORT_COL1, ' ')+sort1Record);
            lineCount[0]++;
        }
        //Resets the counter
        sort1Count =0;


        sort1Desc= getSortDescription(connection, pSort1, sort1GetDescValue, sort1GetDescTable,
                                              sort1GetDescCode, Value1, errors);
    }
sort1Count++; 

我的问题是如何合并重复的项目并总结它们的数量？

例如，我现在的代码只是在我的摘要报告中打印以下内容，

架构 40
工程56
dentry 66
架构16
计算机科学10
工程11
架构5

输出应该是:

架构61
工程67
dentry 66
计算机科学10
架构5

我只是不知道如何做到这一点。我正在考虑使用 HashMap 或哈希集，但我不确定如何使用。感谢任何帮助，谢谢!

Answer 1

如果实在不想在sql中使用聚合，可以使用HashMap<String, Integer> 。类似这样的事情:

Map<String, Integer> aggResult = new HashMap<>();
while (rs.next()) {
    String name = rs.getString(NAME_INDEX); //NAME_INDEX - name column index
    int value = rs.getInt(VALUE_INDEX); //VALUE_INDEX - value column index

    aggResult.merge(name, value, Integer::sum);

    //if you dont have java8 use this "if":
    /*
    if (aggResult.containsKey(name)) {
        Integer sum = aggResult.get(name);
        aggResult.put(name, sum + value);
    } else {
        aggResult.put(name, value);
    }
    */
}
//test output:
aggResult.forEach((key, value) -> System.out.println(key + ": " + value));

也许您需要TreeMap (有或没有比较器)改为 HashMap对于顺序，对 ResultSet 或其他内容中的值进行 null 检查。