How to get float values from sql query

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Manohar Thunga 2018-9-16

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评论： Walter Roberson 2018-9-19

I have following table

        d       dd
      ______    __
      12.345    12
      34.567    34
      45.678    45
  ss = fetch(conn,'SELECT d FROM sc WHERE dd = 12')

when I execute above query, I am getting correct result as

       d   
    ______
    12.345

but following query giving the wrong answer as an empty table

ss = fetch(conn,'SELECT d FROM sc WHERE d = 12.345')

How to resolve this issue

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Ming Yue 2018-9-19

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Hi Manohar,

What version of MATLAB, what database and which version of connector are you using? I think the issue could be platform dependent.

I tested the above scenario on MATLAB R2018a with MySQL 8.0 and ODBC connector 5.3. Here's what I got:

>> ss = fetch(conn,'SELECT d FROM sc WHERE dd = 12')

ss =

1×1 cell array
    {[12.3450]}

>> ss = fetch(conn,'SELECT d FROM sc WHERE d = 12.345')

ss =

1×1 cell array
    {[12.3450]}

>> ss = fetch(conn,'SELECT d FROM sc WHERE d = 12.3456')

ss =

[]

Walter Roberson 2018-9-19

My suspicion is that the data stored is not bit-for-bit identical to however sql translates decimal 12.345 (keeping in mind it is being transferred as text for the purposes of the query). I think the stored 12.345-ish value might be truncated due to printing limitations.

That is why I recommend pulling back whatever is there and subtract 12.345 to see what the difference is

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