Multiplying a range in MySQL - mysql

Question

I have store weight in lbs in my column which I need to convert to KG. I was able to do it with a simple query:
SELECT ( weight * 0.45 ) as weight from TABLE
However, this doesn't work values which are stored as a range, ex. '200 - 300'. If I use the same query it returns 440.925 instead of 440-661. I understand this is happening because I'm multiplying string but is there a way I can multiple a range value (200-300) to get the desired result.
If not, how should I convert this range ideally?

Answer 1

SUBSTRING_INDEX is useful here:
SELECT IF(
INSTR(weight, '-') > 0, /* Does weight contain a dash? */
CONCAT( /* Yes? Multiply each, and return them: */
SUBSTRING_INDEX(weight, '-', 1) * 0.45,
' - ',
SUBSTRING_INDEX(weight, '-', -1) * 0.45
),
weight * 0.45 /* No? Just simply multiply the weight */
) AS `range`
FROM test
First, we check to see if weight contains a dash, and if it does, split it up, and multiply them out individually.
See an example here: https://www.db-fiddle.com/f/iELvWDjpVGBZEkpdR4jtsK/0

Answer 2

If i understand your question correctly you need to do something like below.
SELECT
CONCAT (
SUBSTRING_INDEX(SUBSTRING_INDEX(column, ' - ', 1), ' - ', -1) * 0.45
, ' - '
, SUBSTRING_INDEX(SUBSTRING_INDEX(column, ' - ', 2), ' - ', -1) * 0.45
)
FROM
table
1) Nesting SUBSTRING_INDEX functions makes it possible to extract items from a string.
2) CAST function is not needed because of MySQL autotype cast.

Answer 3

Using CAST, and SUBSTRING_INDEX functions.
CAST will ensure that even if there are more spaces on either side of the '-' (hyphen) character, it will still convert it into a valid number. You can change the DECIMAL(10,4) to any precision, as per your application requirements.
SUBSTRING_INDEX will find the substring before the occurence of '-' (hyphen) character.
Try this:
SELECT
CONCAT(CAST(SUBSTRING_INDEX(weight, '-', 1) AS DECIMAL(10,4)) * 0.45,
'-',
CAST(SUBSTRING_INDEX(weight, '-', -1) AS DECIMAL(10,4)) * 0.45)
AS weight
FROM table