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Problem description

When using pd.read_sql_table() with Oracle DB precision of data type sqlalchemy.dialects.oracle.NUMBER is lost.

Expected Output

Precision should not be lost as this datatype can be either integer or float.

The problem

Looks like the root cause for this is in _harmonize_columns(), particularly in _get_dtype() that is used there. The SQLAlchemy type sqlalchemy.dialects.oracle.NUMBER is based on both sqlalchemy.types.Numeric and sqlalchemy.types.Integer. As there is no support for SQLAlchemy Numeric type in _get_dtype() this Oracle type is being treated as integer and precision is dropped when using astype() in _harmonize_columns() itself.