ignoring condition in where clause in mysql

Question

Can we write conditional where clause in mysql? I know one way ie with CASE WHEN

But my condition is if where clause fails then ignore it and execute query as there was no where clause

eg. I want to select persons in particular city. but if I got city null as input then ignore that statement and return all persons in all cities

Can someone please tell me how to do this

please Help!!

Answer 1

像这样的东西？

select p from Person p where (:city is null or p.city = :city)

Answer 2

select * from your_table
where @city is null 
or city = @city