Fixed a terrible diff issue case of PostgreSQL

[Code-Hex]

Why terrible?

• It outputs syntax that will result in an error when executed.
  ALTER TABLE tablename ALTER colname TYPE serial;
• When parsing from DBI, unexpected types are returned
• Similarly, unexpected sizes are returned
• There is no type match for time

What I did?

• I rewrote SQL to solve the above problem.
• Added a dedicated parser statement for smallserial.
• When type like serial, we modified it to use CREATE SEQUENCE instead of ALTER.

Best regard 👍