Better way to write these SQL statements - mysql

Question

I want to read data for reporting purpose. Currently, I populate a table using another table's calculated data, and read data for reporting from the populated table. My current logic is too delete the old data, and insert the new data, all within a transaction.
UPDATE
Requirements
1) The logic below is to run once every second. Please note that other processes also udpates tableB with the same refresh rate.
2) TableB is used for reporting purpose. TableA and TableB resides in different databases.
3) TableB contains around 10 millions rows, around 4 millions rows will be updated once every second by the code below. Other processes also update the other part of data (6 = 10-4 millions) in tableB at the same refresh rate.
My concern is that:
1) three statements use similar sum, and where clauses, which might be improved.
2) There are about 1-2 millions row in tablea to update to tableB. Using an explicit temporary table might slow down.
3) Using transaction might slow down, but it seems the only way.
4) Update the data might be a better option than delete and insert (which one should I choose?)
I want to find a better performant way (including table redesign etc.). Below is the current way:
pseudocode below:
start/begin transaction here
DELETE from tableb data that I want to insert below, e.g. delete data where Code = 'code'
INSERT INTO tableb(Code, Total)
SELECT sum(a.Code, price)
FROM tablea a
GROUP BY a.Code;
IINSERT INTO tableb(Code, Total)
SELECT sum(a.Code price) -- use price
FROM tablea a
WHERE a.meanPrice IS NOT NULL
GROUP BY a.Code;
INSERT INTO tableb(Code, Total)
SELECT sum(a.Code, meanPrice ) -- use meanPrice
FROM tablea a
WHERE a.meanPrice IS NOT NULL
GROUP BY a.Code;
Commit transaction here
It is for MySQL, but ideally it should be generic.
Any idea?

Answer 1

Do you actually need to update values in the table? They are not tagged with any id or names to identify them.
The following SELECT statement returns the data you want:
SELECT code,
sum(price),
sum(case when a.meanPrice is not null then price else 0 end),
sum(case when a.meanPrice is not null then meanprice else 0 end)
FROM tablea a
GROUP BY a.Code;
If you needed to insert this into a temp table, you can unpivot the data. However, that format does not make sense to me. Can you explain why you are using a table with one numeric column in this way?

Answer 2

This query does your INSERT task in 1 step, but ... kids, don't do this at home without actually measuring actual performance:
http://sqlfiddle.com/#!2/381e2/9
INSERT INTO tableb(Total)
SELECT
CASE
WHEN t.v = 1
THEN SUM( price )
WHEN t.v = 2
THEN SUM(
CASE
WHEN meanPrice IS NOT NULL THEN price
ELSE 0
END
)
WHEN t.v = 3
THEN SUM( meanPrice )
END AS Total
FROM tablea
INNER JOIN
( SELECT 1 AS v UNION ALL
SELECT 2 AS v UNION ALL
SELECT 3 AS v
) AS t
GROUP BY tablea.Code, t.v;

Answer 3

Point 3 is false.
Solution 1: Create an store procedure.
Solution 2: Create a trigger on the impacted tables.
Solution 3: Don't ask for a sum every time, do the sum the first time and then save the number on another table. On every modification of this table, do the sum over your new table, I wont be 1 millions records, only one per table.
Pivot tables!