坚持一个简单的查询 - OUTER JOIN - 编程

I have a simple query to get, but I'm stuck and I really can't figure out how to do this. More specifically: The table Allarmi has a lot of entries, which i show all grouped by Allarmi.IDComponente

我有一个简单的查询,但我卡住了,我真的无法弄清楚如何做到这一点。更具体地说:表Allarmi有很多条目,我显示所有条目由Allarmi.IDComponente分组

something like this

这样的事情

SELECT * 
FROM ALLARMI AS ALLARMI
WHERE ID_CELLA = 1
GROUP BY ID_Componente

I only need to add to this table a COUNT column, something like

我只需要在这个表中添加一个COUNT列,就像这样

(SELECT COUNT( * ) 
FROM allarmi
WHERE isAttivo = 1
GROUP BY id_componente)

but I would like to show COUNT even when its 0 or NULL

但我想显示COUNT,即使它的0或NULL

How can I do it? Thanks in advance

我该怎么做?提前致谢

1 个解决方案

#1

Assuming table Componenti defines the components, and you want to get a count of records from allarmi for each component, what you actually want to do is select the component from Componenti and add a LEFT OUTER JOIN on allarmi

假设表Componenti定义了组件,并且您希望从allarmi获取每个组件的记录计数,您实际想要做的是从Componenti中选择组件并在allarmi上添加LEFT OUTER JOIN

SELECT COMPONENTI.ID_Componente, COUNT(ALLARMI.ID_Componente)
FROM COMPONENTI
LEFT OUTER JOIN ALLARMI ON
   -- insert your join here!
   -- maybe COMPONENTI.ID_Componente= ALLARMI.ID_Componente?
   -- add any query for this table here as well.
   AND ALLARMI.ID_Cella = 1
GROUP BY COMPONENTI.ID_Componente

坚持一个简单的查询 - OUTER JOIN

1 个解决方案

#1

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