Question

我有三个表：客户，收据，薪水

Customers
 Id    Name    
  1    john

Receipts
Id    Amount 
1      500
2      250
3      600
4      700

Salary
Id   Amount 
1    300
2    300
3    680

我想找一些与约翰相关的工资和收据。我认为这是简单的sql语句，如：

select  cus.Name, sum(sal.Amount) as Salary, sum(re.Amount) as Recieved 
from Customers as cus inner join Salaries as sal on cus.Id = sal.Id
inner join Receipts as re on cus.Id = re.Id
where cus.Id= 1
Group by cus.Name

但我发现结果更大

Name    Salary   Recieved
john    6150      4320

当我编写没有sum的查询时：

select  cus.Name, sal.Amount as Salary, re.Amount as Recieved 
    from Customers as cus inner join Salaries as sal on cus.Id = sal.Id
    inner join Receipts as re on cus.Id = re.Id
    where cus.Id= 1

我得到了这些重复记录

    john    500 100
    john    500 300
    john    500 680
    john    250 100
    john    250 300
    john    250 680
    john    600 100
    john    600 300
    john    600 680
    john    700 100
    john    700 300
    john    700 680

为什么内部联接行为像这样？我希望得到一次记录，但重复4次！我是否必须尝试子选择查询？

Answer 1

查询看起来正确。

http://www.sqlfiddle.com/#!9/1b5157/1

您的近似查询有一个小提琴，它按预期工作。因此，如前所述，由于您有CustomerOrSupplier，您可能会加入错误的表

Answer 2

select  cus.Name, 
        sum(sal.Amount) as Salary, 
        sum(re.Amount) as Recieved 
from Customers as cus 
inner join Salary as sal 
on cus.Id = sal.Id
inner join 
Receipts as re 
on cus.Id = re.Id
Group by cus.Name;

<强>演示

http://sqlfiddle.com/#!18/956fb/10

Answer 3

我发现问题恰好是表名称之一。

更改以下内容：

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.beans.PropertyVetoException;
import java.beans.VetoableChangeListener;


public class Square extends Canvas implements VetoableChangeListener, PropertyChangeListener {
    private final int SIZE = 100;
    private int side = 1;
    public Square() {
        setSize(SIZE,SIZE);
    }

    public void vetoableChange(PropertyChangeEvent pce) throws PropertyVetoException {
        if ((pce.getPropertyName()).equals("value")) {
            int v = (Integer)pce.getNewValue();
            if ((v <=0)||(v > SIZE/2))
                throw new PropertyVetoException ("Value out of bounds!", pce);        
        }   
    }

    public void propertyChange(PropertyChangeEvent pce) {
        if ((pce.getPropertyName()).equals("value")) {
            setSide((Integer)pce.getNewValue());
            repaint();
        }
    }

    public void setSide(int side) {
        this.side = side;
    }

    public int getSide() {
        return this.side;
    }

    public void paint (Graphics g) {
        Dimension d = getSize();
        g.setColor(Color.BLUE);
        g.drawRect(d.width/2 - side, d.height/2 - side, side*2, side*2);
    }

}

为：

from Customers as cus inner 
join Salaries as sal 
on cus.Id = sal.Id

我在内连接中获得了3个表的重复数据

3 个答案: