...

 If the column definition is specificed, it will use the defined column to  create the new table.  Otherwise, it'll retrieve the column definition from the sub-query.

2: Check the table exists or not. If the table doesn't exist, throw TableException("").

3: Call method try to get Tow. If, it means the repla will be done by 

4: If , it means which means the automic can not be guarrantten. Flink will apply the Replace automici. More extacly, it will drop the old table, create the new table, insert data into the new tables.

Note: these three steps are not done in auctom,

For CREATE OR REPLACE TABLE AS  stament,  when the table exists, it'll consider it as REPLACE TABLE AS  statement. Otherwise, it'll consider it as CREATE TABLE AS  statement. 

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users? 
• If we are changing behavior how will we phase out the older behavior? 
• If we need special migration tools, describe them here.
• When will we remove the existing behavior?

Test Plan

No any compatibility problem.

Test Plan

UT & ITDescribe in few sentences how the FLIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

Rejected Alternatives

If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.