The 1st query calls row(1), row(4) and the 2nd query calls row(2) and row(4).
The 1st query UNION the 2nd query calls row(1), row(2) and row(4).
Then, How can I call common row only?
The 1st query OPPOSITE of UNION 2nd query calls row(4) only.
Is there any operator or function which is OPPOSITE of UNION?
Normally you would do that with an INTERSECT (which is the opposite of union), but as far as I know MySQL doesn’t support INTERSECT.
So what you could do is something like:
field IN (<second select query>)
you can do several unions so lon as you ensure they return the same number of values
from table 1 AS t1
from table AS t2
from table AS t3
Thats not a full query but is meant to show how using NULL can let you have a query with differing numbers of columns in each union. ALso meant to show UNION ALL, which you can google for.