MYSQL usng derived value in select multiple times

WhiffWham :

Is it possible to do something like the following?

select a as res, res * 2 as res2, res2 * 4 from tableA;

The instance I want to do this is much more complicated and it would make the query much more manageable if there was a way to not have to duplicate logic.

I was thinking a function would work but then I would not have the row by row action that the select allows for.

SELECT
    comp.playerID,
    comp.RC,
    comp.RC / (t.BPF + 100) / 200
FROM
    (
        SELECT
            playerID,
            coalesce(
                (sum(H) + sum(2B) + (2 * sum(3B)) + (3 * sum(HR))) + ((sum(BB) + sum(HBP) - sum(IBB)) * 0.26) - (sum(SH) + sum(SF) + sum(SB)) * 0.52,
                0
            ) AS RC
        FROM
            Batting
        GROUP BY
            playerID
    ) AS comp,
    Teams t;

There are a few nested layers outside of this, but this is the root of the duplication.

Barmar :

You can't refer to an alias in the same SELECT list. You need to use a subquery.

SELECT res, res * 2, res * 8
FROM (
    SELECT a AS res
    FROM tableA
) AS x

In your larger query, you're getting a full cross product between comp and teams, so you're duplicating each player on each team. You need to join the tables based on the player's team.

SELECT
    comp.playerID,
    comp.RC,
    comp.RC / (t.BPF + 100) / 200
FROM
    (
        SELECT
            playerID,
            teamID,
            coalesce(
                (sum(H) + sum(2B) + (2 * sum(3B)) + (3 * sum(HR))) + ((sum(BB) + sum(HBP) - sum(IBB)) * 0.26) - (sum(SH) + sum(SF) + sum(SB)) * 0.52,
                0
            ) AS RC
        FROM
            Batting
        GROUP BY
            playerID
    ) AS comp
JOIN Teams t ON comp.teamID = t.teamID

You didn't post your schema, so I had to guess at how the tables are related. You should be able to adjust the answer to the actual relationship (e.g. if there's a join table that relates players to teams, add another join).