Wrong type inference on postgres difference between TIMESTAMPs should be INTERVAL

[simon-pactum]

Discovered in sqlmesh, not sure if bug belongs here or in sqlglot, but with a sqlmesh model like:

SELECT CURRENT_TIMESTAMP - CURRENT_TIMESTAMP as delta;

The type of delta in columns_to_types is reported as TIMESTAMP but it actually has type INTERVAL. Leading to crash when creating model as it tries to do an invalid cast.

import sqlglot

expr, = sqlglot.parse("SELECT CURRENT_TIMESTAMP - CURRENT_TIMESTAMP as delta", dialect='postgres')
opt = sqlglot.optimizer.optimize(expr, dialect='postgres')

print(repr(opt))

Select(
  expressions=[
    Alias(
      this=Sub(
        this=CurrentTimestamp(_type=DataType(this=Type.TIMESTAMP)),
        expression=CurrentTimestamp(_type=DataType(this=Type.TIMESTAMP)),
        _type=DataType(this=Type.TIMESTAMP)),
      alias=Identifier(this='delta', quoted=True, _type=DataType(this=Type.UNKNOWN)),
      _type=DataType(this=Type.TIMESTAMP))],
  _type=DataType(this=Type.UNKNOWN))