多线程优化无效(其中一个线程执行10秒导致)

尽量避免循环写sql,row_number 实际基本应用

一、原来sql

java 复制代码

    // 原来是 t1 表和t2 表关联,查t1的code,同时要是t2 表某个属性xx 降序后取一个
    String sql ="    SELECT t1.*, t2.xx, " +
            "    FROM table1 t1 " +
            "    LEFT JOIN table2 t2 ON t1.id = t2.table1_id " +
            "    WHERE t1.code = '{}' order by t2.xx desc fetch first 1 rows only ";
//    在循环中写sql
    for(YourObject item : objectList){
        String code = item.getCode();
        Map<Stirng,Object> resultMap = getSqlMapper().selectOne(strUtil.format(sql,code));
//        查出结果继续别的处理
    }

二、优化后sql

java 复制代码

    public void processWithRowNumber(List<YourObject> objectList) {
        if (objectList.isEmpty()) return;
        
        Set<Long> codeSet = objectList.stream()
            .map(YourObject::getCode)
            .collect(Collectors.toSet());
        
        String inClause = codeSet.stream()
            .map(String::valueOf)
            .collect(Collectors.joining(","));
        
        // 使用ROW_NUMBER()为每个ID分组，取最新的一条
        String sql = "SELECT * FROM (" +
                     "    SELECT t1.*, t2.xx, " +
                     "           ROW_NUMBER() OVER (PARTITION BY t1.id ORDER BY t2.xx DESC) as rn " +
                     "    FROM table1 t1 " +
                     "    LEFT JOIN table2 t2 ON t1.id = t2.table1_id " +
                     "    WHERE t1.code IN (" + inClause + ")" +
                     ") WHERE rn = 1";
        
        List<Map<String, Object>> results = sqlMapper.selectList(sql);
        
        // 构建映射关系
        Map<Long, Map<String, Object>> resultMap = results.stream()
            .collect(Collectors.toMap(
                result -> ((Number) result.get("CODE")).longValue(),
                result -> result
            ));
        
        // 处理结果
        for (YourObject obj : objectList) {
            Map<String, Object> result = resultMap.get(obj.getCode());
            if (result != null) {
                processSingleResult(obj, result);
            }
        }
    }

三、总结

这是row_number 实际基本应用（用于优化sql放在循环外）

将sql拿出循环就是用row_number() over()原因

之前博客记录 row_number用法 Row number 函数用法

实际项目使用过 row_number 实际基本应用