Question

有两个表产品，颜色产品与颜色之间存在一对多关系。

产品表： ID，标题，说明

颜色表： ID，PRODUCT_ID，COLOR_NAME

现在我想做一个选择产品的查询，其中颜色表中包含所有（例如）三种颜色（＆＃39;红色＆＃39;，＆＃39;绿色＆＃39; ＆＃39;褐色＆＃39）

Answer 1

一种方法是：

select c.product_id
from colors c
where c.color_name in ('red', 'green', 'brown')
group by c.product_id
having count(distinct color_name) = 3;

Answer 2

如果要从colors表格中选择所有颜色，请尝试以下查询。

它将选择所有颜色，不限于3种颜色

SELECT c.product_id
FROM colors c
WHERE c.color_name IN (SELECT DISTINCT color_name FROM colors)
GROUP BY c.product_id
HAVING COUNT(DISTINCT color_name) = (SELECT COUNT(DISTINCT color_name) FROM colors);

如果您需要获取产品的标题和描述，那么：

SELECT * FROM products WHERE id in (
SELECT c.product_id
FROM colors c
WHERE c.color_name IN (SELECT DISTINCT color_name FROM colors)
GROUP BY c.product_id
HAVING COUNT(DISTINCT color_name) = (SELECT COUNT(DISTINCT color_name) FROM colors));

Answer 3

HAVING是要走的路。

package com.example;

import java.util.Iterator;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

public class CompletionIterator<T> implements Iterator<T>, AutoCloseable {

    private AtomicInteger count = new AtomicInteger(0);

    private CompletionService<T> completer;

    private ExecutorService executor = Executors.newWorkStealingPool(100);

    public CompletionIterator() {
        this.completer = new ExecutorCompletionService<>(executor);
    }

    public void submit(Callable<T> task) {
        completer.submit(task);
        count.incrementAndGet();
      }

    @Override
    public boolean hasNext() {
        return count.decrementAndGet() > 0;
    }

    @Override
    public T next() {
        try {
            return completer.take().get();
        } catch (InterruptedException | ExecutionException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public void close() {
        try {
            executor.shutdown();
            executor.awaitTermination(Long.MAX_VALUE, TimeUnit.MILLISECONDS);
            executor = null;
            completer = null;
            count = null;
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }

}

列一对多关系的三个条件

3 个答案: