add 'create_table_if_not_exist' params

[Joongho]

This is useful when merge operation.

1. create temp table A (like schema.A) -> run by preactions
2. load into table A ( dbtable = A )
3. update/insert -> run by postactions

Above scenario, table A(=dbtable) should not be created

[kyrozetera]

How is this different than setting a SaveMode?

[Joongho]

It's upsert(=merge) operation.

schema.A is final target table, A is temp table.

1. update schema.A set ... where schema.A.pk1 = A.pk1 and schema.A.pk2 = A.pk2 ...
2. insert int schema.A
   select * from A s
   left join schema.A t
   on t.pk1=s.pk1 and t.pk2=s.pk2
   where t.pk1 is null and t.pk2 is null ...