real data type is float32 in PG database, but in the datafusion it is as float64

[liukun4515]

Describe the bug
In the PG database, the real datatype is as the float32, but it is as float64 in the datafusion.

Do we need to be consistent with PG database in the point?

1. https://github.com/apache/arrow-datafusion/blob/3bf5811b9a275b7ce6792867a5c1fa230a880742/datafusion/src/catalog/information_schema.rs#L416
2. https://github.com/apache/arrow-datafusion/blob/414c826bf06fd22e0bb52edbb497791b5fe558e0/datafusion/src/sql/planner.rs#L377

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Expected behavior
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[liukun4515]

@alamb @houqp do you think we should make consistent with the PG datatype ?

[houqp]

I think so considering we aim to be compatible with postgres