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Fixes to several issues around view update generation, pertaining to
timestamp and TTL management.
Fixes#3361Fixes#3360Fixes#3140
Refs #3362
Tests: unit(release, debug), dtest(materialized_views.py)
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Reviewed-by: Nadav Har'El <nyh@scylladb.com>
* 'materialized-views/fixes-galore/v2' of http://github.com/duarten/scylla:
mutation_partition: Clarify comment about emptiness
tests: Add view_complex_test
tests/view_schema_test: Complete test
db/view: Move cells instead of copying in add_cells_to_view()
db/view: Handle unselected base columns and corner cases
mutation_partition: Regular base column in view determines row liveness
db/view: Don't avoid read-before-write when view PK matches base
db/view: Process base updates to column unselected by its views
db/view: Consider partition tombstone when generating updates
tests/view_schema_test: Remove unneeded test
mutation_fragment: Allow querying if row is live
view_info: Add view_column() overload
view_info: Explicitly initialize base-dependent fields
cql3/alter_table_statement: Forbid dropping columns of MV base tables