Question

这可能很简单，但是找不到正确的搜索词，因此，如果重复搜索，就很可能会在某个地方找到答案。

我设置了以下表格

CREATE TABLE IF NOT EXISTS `customer` (
  `id` int(6) unsigned auto_increment NOT NULL,
  `name` varchar(200) NOT NULL,
  PRIMARY KEY (`id`)
) DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `billing_run` (
  `id` int(6) unsigned auto_increment NOT NULL,
  `date` datetime NOT NULL,
  PRIMARY KEY (`id`)
) DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `invoice` (
  `id` int(6) unsigned auto_increment NOT NULL,
  `billing_run_id` int(6) unsigned NOT NULL,
  `customer_id` int(6) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  FOREIGN KEY (billing_run_id) REFERENCES billing_run(id),
  FOREIGN KEY (customer_id) REFERENCES customer(id)
) DEFAULT CHARSET=utf8;

具有以下数据

insert into customer (name) values ('test customer');
insert into billing_run (date) values ('2019-01-01 12:00:00');
insert into billing_run (date) values ('2019-02-01 12:00:00');
insert into billing_run (date) values ('2019-03-01 12:00:00');
insert into invoice (customer_id,billing_run_id) values (1,1);

SQLFiddle此处-> http://sqlfiddle.com/#!9/a54162/5

我想获取customer与invoice相关且billing_run为2的id不相关的记录

我的查询

select c.id from customer c
left join invoice i on i.customer_id = c.id
left join billing_run br on br.id = i.billing_run_id and br.id = 2
where i.id is null

返回0条记录。为什么？

Answer 1

首先，将表customer（1行）与表invoice（1行）连接。此联接将返回1行，因为ON子句中的列之间存在匹配项：

on i.customer_id = c.id

（示例数据中i.customer_id和c.id的值均为1）。
因此，i.id is null没有任何行。
表billing_run的下一个联接不影响前2个联接的表。
所以条件：

where i.id is null

不返回任何行。
正确的条件（您在原始小提琴中具有的条件）是：

where br.id is null

因为对表billing_run的联接将为该条件返回不匹配的行：

on br.id = i.billing_run_id and br.id = 2

因为i.billing_run_id = 2中没有invoice。

Answer 2

您将要执行一个排他的where子句，该子句将返回所需的1行。

select * from customer c 
where c.id not in (Select customer_id from invoice i LEFT JOIN billing_run br on 
i.billing_run_id=br.id WHERE br.id=2 and br.id is not null)

http://sqlfiddle.com/#!9/a54162/14

Answer 3

您不需要billing_run表。所以我认为您打算：

select c.id
from customer c left join
     invoice i
     on i.customer_id = c.id and i.billing_run_id = 2
where i.id is null

左联接特定行

3 个答案: