update problems_with_date_time.md

update problems_with_date_time.md

create 5.problems_with_date_time.md

update EXPLAIN_example.md

create 6.EXPLAIN_example.md

update what_is_EXPLAIN_and_how_to_use_it.md

create what_is_EXPLAIN_and_how_to_use_it.md

update defining_window_function.md

create defining_window_function.md

update subqueries_vs_cte.md

create subqueries_vs_cte.md

update 4.DDL_DML/declarative_partitioning/declarative_partitioning.md

create 4.DDL_DML/declarative_partitioning/declarative_partitioning.md

update 3.ОсновыSQL/EXCEPT_и_INTERSECT/except_intersect.md

create 3.ОсновыSQL/EXCEPT_и_INTERSECT/except_intersect.md

update regexp.md

create regexp.md

update statistic_aggregate_functions.md