Rails where condition with nil value

Question

I found out that using where with symbol :my_id => nil and using old school one with ? is different. Could anyone explain me why?

MyTable.where(\"my_id = ? \", n         


        

Answer 1

For any relational database the predicate (my_id = NULL ) is always false, because NULL never equals anything - not even NULL.

A more complete explanation is here https://dba.stackexchange.com/questions/166579/why-is-null-ignored-in-query-results/166586#166586.

ActiveRecord will cope with this very well, even when null is included in an array.

irb(main):029:0> Book.where(id: 1).to_sql
=> "SELECT ... WHERE \"books\".\"id\" = 1"
irb(main):030:0> Book.where(id: nil).to_sql
=> "SELECT ... WHERE \"books\".\"id\" IS NULL"
irb(main):031:0> Book.where(id: [1, nil]).to_sql
=> "SELECT ... WHERE (\"books\".\"id\" = 1 OR \"books\".\"id\" IS NULL)"