How to declare a variable in MySQL?

Question

How to declare a variable in mysql, so that my second query can use it?

I would like to write something like:

SET start = 1;
SET finish = 10;

SELECT         


        

Answer 1

For any person using @variable in concat_ws function to get concatenated values, don't forget to reinitialize it with empty value. Otherwise it can use old value for same session.

Set @Ids = '';

select 
  @Ids := concat_ws(',',@Ids,tbl.Id),
  tbl.Col1,
  ...
from mytable tbl;