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pythonmysqlpandasinteger

Pandas read sql integer became float

When I use pandas to read a MySQL table, some columns (see 'to_nlc' in the image below) that used to have an integer type became a floating-point number (automatically append .0).

Can anyone figure out why this happens? Or at least have a guess?

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Solution

  • Problem is your data contains NaN values, so int is automatically cast to float.

    I think you can check NA type promotions:

    When introducing NAs into an existing Series or DataFrame via reindex or some other means, boolean and integer types will be promoted to a different dtype in order to store the NAs. These are summarized by this table:

    Typeclass   Promotion dtype for storing NAs
floating    no change
object      no change
integer     cast to float64
boolean     cast to object

    While this may seem like a heavy trade-off, in practice I have found very few cases where this is an issue in practice. Some explanation for the motivation here in the next section.