Question

For example, i have an empty table ‘A’ with columns: number(INT) and id.
I know that in MySQL null + number returns null. However there is workaround using IFNULL function:

SELECT IFNULL(NULL, 0) + @number

would return @number. But if I try to select from an existing table, results are not the same:

SELECT IFNULL(number, 0) + @number FROM A 

gives me a result with no rows selected.

How can i get MySQL to display one row with ‘number’ being a number, so I could insert minimal @number using REPLACE statement into table A?
Maybe there is another way..?

Answer 1

If this is indeed some aggregate function then something along these lines will always return 1 row

select MIN(IFNULL(tablesum.mysum, 0))
from 
  (select MIN(t.score) mysum from table t    
   union all 
   select @number as mysum
  ) tablesum

Reading your comment I think you want
Select min of a table (0 or 1 row), combine that with a row with a fixed number then sum those 1 or 2 rows:

select SUM(IFNULL(d.number, 0))
from 
  (select MIN(t.number) number from table t    
   union all 
   select @number as number
  ) d