Question

I have two tables. tl and t2. Each table has the columns: ID, name. The ID is a PK and Auto increment. The two tables are not connected to each other. The t2.name is a subset of t1.name, but after adding www. at the beginning of the string in the name.
Ex:

`t1`.`name`= ggg
`t2`.`name`= www.ggg

What I am trying to do is: selecting all the record of where t1.name not inserted in t2. So I wrote the following query:

select concat('www.',name) 
from db.t1
LEFT JOIN db.t2 
ON t2.name = t1.name
WHERE NOT EXISTS (select name from db.t2);

But, I get 0 result. I am certain that there are records that are available in t1 but not in t2. How can I select all the names in t1 that are not in t2??

Answer 1

select concat('www.',name) 
from db.t1
LEFT JOIN db.t2 ON t2.name = concat('www.', t1.name)
WHERE db.t2.name IS NULL