Merge pull request ClickHouse#80653 from rschu1ze/docs-join-settings

Update settings descriptions of two join optimizations

Author: rschu1ze

src/Core/Settings.cpp

@@ -2021,7 +2021,7 @@ DECLARE(BoolAuto, query_plan_join_swap_table, Field("auto"), R"(
 )", 0) \
     \
     DECLARE(Bool, query_plan_join_shard_by_pk_ranges, false, R"(
-Apply sharding for JOIN if join keys contain a prefix of PRIMARY KEY for both tables. Supported for hash, parallel_hash and full_sorting_merge algorithms
+Apply sharding for JOIN if join keys contain a prefix of PRIMARY KEY for both tables. Supported for hash, parallel_hash and full_sorting_merge algorithms. Usually does not speed up queries but may lower memory consumption.
  )", 0) \
     \
     DECLARE(UInt64, preferred_block_size_bytes, 1000000, R"(
@@ -5267,7 +5267,7 @@ Allow to convert OUTER JOIN to INNER JOIN if filter after JOIN always filters de
 Allow to merge filter into JOIN condition and convert CROSS JOIN to INNER.
 )", 0) \
     DECLARE(Bool, query_plan_convert_join_to_in, false, R"(
-Allow to convert JOIN to subquery with IN if output columns tied to only left table
+Allow to convert JOIN to subquery with IN if output columns tied to only left table. May cause wrong results with non-ANY JOINs (e.g. ALL JOINs which is the default).
 )", 0) \
     DECLARE(Bool, query_plan_optimize_prewhere, true, R"(
 Allow to push down filter to PREWHERE expression for supported storages