Question

i have a query like this:

ID    |    name                     |    commentsCount
1     |    mysql for dummies        |    33
2     |    mysql beginners guide    |    22

SELECT
    ...,
    commentsCount    // will return 33 for first row, 22 for second one
FROM
    mycontents
WHERE
    name LIKE "%mysql%"

also i want to know the total of comments, of all rows:

SELECT
    ...,
    SUM(commentsCount) AS commentsCountAggregate    // should return 55
FROM
    mycontents
WHERE
    name LIKE "%mysql%"

but this one obviously returns a single row with the total.

now i want to merge these two queries in one single only,

because my actual query is very heavy to execute (it uses boolean full text search, substring offset search, and sadly lot more), then i don’t want to execute it twice

is there a way to get the total of comments without making the SELECT twice?

!! custom functions are welcome !!

also variable usage is welcome, i never used them…

Answer 1

One obvious solution is storing intermediate results withing another ‘temporary’ table, and than perform aggregation in the second step.

Another solution is preparing a lookup table containing sums you need (but there obviously needs to be some grouping ID, I call it MASTER_ID), like that:

CREATE TABLE comm_lkp AS
SELECT MASTER_ID, SUM(commentsCount) as cnt
FROM mycontents
GROUP BY MASTER_ID

Also create an index on that table on column MASTER_ID. Later, you can modify your query like that:

SELECT
    ...,
    commentsCount,
    cnt as commentsSum
FROM
    mycontents as a
        JOIN comm_lkp as b ON (a.MASTER_ID=b.MASTER_ID)
WHERE
    name LIKE "%mysql%"

It also shouldn’t touch your performance as long as lookup table will be relatively small.