Question

I’m still learning SQL so I was wondering if there is a better way of doing the following.

I need to get row data for the lowest and highest values in a column (lets call it columnA).
I would use:

SELECT *
  FROM table
 ORDER BY columnA
  DESC LIMIT 1

Problem is I get only one result due to the LIMIT 1 but there may be identical lowest / highest values in ColumnA that have different values in the other columns. I need those other rows too.

There is SELECT(MAX) but I believe that will also only produce one row of data.

The ways I can think do this are by putting the highest / lowest columnA values into a variable and then back into a second query OR use a LEFT JOIN on alias tables to do this in single query but is there any more direct method?

Answer 1

The simplest way is to perform a sub-query:

SELECT * FROM MyTable WHERE columnA = (SELECT MAX(columnA) FROM MyTable);

You can even query both extremes at once:

SELECT * FROM MyTable
WHERE columnA = (SELECT MAX(columnA) FROM MyTable);
   OR columnA = (SELECT MIN(columnA) FROM MyTable);

I haven’t tested the next one (don’t know if MySQL supports UNION in
sub-queries), but it should work as well, might be a bit more
efficient (depending on your data size).

SELECT * FROM MyTable
WHERE columnA IN (
    SELECT MAX(columnA) FROM MyTable
    UNION
    SELECT MIN(columnA) FROM MyTable
);