MySQL Join - Not unique table/alias error

Question

I am trying to join 2 tables but i got an error

'not unique table/alias: 'ct'

query is

select em.* ,ct.Cities_NAME
from Customer em,
     Cities ct inner join Cities ct on ct.Cities_ID = em.Customer_CITY 
where Customer_GROUP is NULL and Customer_ENABLED is not FALSE and Customer_TYPE != 'User'

where is the mistake and why?

Answer 1

Never use commas in the FROM clause. Always use proper, explicit, standard JOIN syntax:

select em.*, ct.Cities_NAME
from Customer em inner join
     Cities ct
     on ct.Cities_ID = em.Customer_CITY 
where em.Customer_GROUP is NULL and
      em.Customer_ENABLED and
      em.Customer_TYPE <> 'User';

For some reason, you have listed ct twice in the query. You should also qualify all column references in the query.