I'm doing
我在做
Event.where(state: nil) and get 1 result, but for Event.where('state = ?', nil) get 0 results.
事件。其中(state: nil)得到1个结果，但对于事件。其中(state = ?'， nil)得到0个结果。
What's the difference between these?
它们之间有什么区别?
2 个解决方案
#1
5
where(state: nil) evaluates to WHERE events.state IS NULL and other one evaluates to WHERE (state = NULL) in SQL.
where(state: nil)计算事件。状态为NULL，另一个值计算到SQL中的WHERE (state = NULL)。
Now, A NULL compared to anything returns NULL, except if you use IS operators. So, if you want to check if it is NULL then use state IS NULL, if not NULL then state IS NOT NULL.
现在，与任何返回NULL的值相比，空值都是NULL，除非使用的是操作符。如果你想检查它是否为空，那么use state为空，如果不是空，那么state为非空。
state = NULL, returns NULL, which, in WHERE clause, is equivalent to FALSE, that is why you got 0 records.
状态= NULL，返回NULL，在WHERE子句中，它等于FALSE，这就是为什么有0个记录。
events.state IS NULL is the correct null comparisons so you got the output as you have in DB.
事件。状态为NULL是正确的空值比较所以就得到了DB中的输出。
#2
1
They generate different sql. When you have questions like this you can add a .to_sql to your relation and it will show you the sql that is generated and sent to the database.
他们产生不同的sql。当您有这样的问题时，您可以向您的关系添加.to_sql，它将显示生成并发送到数据库的sql。
Event.where(state: nil) produces this, which checks if x is a null like value
事件。这里(state: nil)生成这个，它检查x是否为空值
... WHERE events.state IS NULL
Event.where('state = ?', nil) produces this, which checks if X equals null which will never be true
事件。这里(state = ?， nil)产生了这个，它检查X是否等于null这永远都不会是真的
... WHERE (state = NULL)
#1
5
where(state: nil) evaluates to WHERE events.state IS NULL and other one evaluates to WHERE (state = NULL) in SQL.
where(state: nil)计算事件。状态为NULL，另一个值计算到SQL中的WHERE (state = NULL)。
Now, A NULL compared to anything returns NULL, except if you use IS operators. So, if you want to check if it is NULL then use state IS NULL, if not NULL then state IS NOT NULL.
现在，与任何返回NULL的值相比，空值都是NULL，除非使用的是操作符。如果你想检查它是否为空，那么use state为空，如果不是空，那么state为非空。
state = NULL, returns NULL, which, in WHERE clause, is equivalent to FALSE, that is why you got 0 records.
状态= NULL，返回NULL，在WHERE子句中，它等于FALSE，这就是为什么有0个记录。
events.state IS NULL is the correct null comparisons so you got the output as you have in DB.
事件。状态为NULL是正确的空值比较所以就得到了DB中的输出。
#2
1
They generate different sql. When you have questions like this you can add a .to_sql to your relation and it will show you the sql that is generated and sent to the database.
他们产生不同的sql。当您有这样的问题时，您可以向您的关系添加.to_sql，它将显示生成并发送到数据库的sql。
Event.where(state: nil) produces this, which checks if x is a null like value
事件。这里(state: nil)生成这个，它检查x是否为空值
... WHERE events.state IS NULL
Event.where('state = ?', nil) produces this, which checks if X equals null which will never be true
事件。这里(state = ?， nil)产生了这个，它检查X是否等于null这永远都不会是真的
... WHERE (state = NULL)