Backport ClickHouse#83118 to 25.6: Do not use unrelated parts of a shared dictionary in the lowCardinalityKeys function

Author: robot-clickhouse

src/Functions/lowCardinalityKeys.cpp

@@ -41,11 +41,12 @@ class FunctionLowCardinalityKeys: public IFunction
         return type->getDictionaryType();
     }
 
-    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t /*input_rows_count*/) const override
+    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t input_rows_count) const override
     {
         const auto & arg = arguments[0];
         const auto * low_cardinality_column = typeid_cast<const ColumnLowCardinality *>(arg.column.get());
-        return low_cardinality_column->getDictionary().getNestedColumn()->cloneResized(arg.column->size());
+        /// In the case of a shared dictionary, we want only dictionary keys that correspond to this block:
+        return low_cardinality_column->cutAndCompact(0, input_rows_count)->getDictionary().getNestedColumn()->cloneResized(arg.column->size());
     }
 };
 

tests/queries/0_stateless/00688_low_cardinality_serialization.reference

@@ -1,8 +1,8 @@
 NativeReader
 LowCardinality(String)	123_a	2	
-LowCardinality(String)	123_bb	3	123_
-LowCardinality(String)	123_	1	123_a
-LowCardinality(String)	123_a	2	123_bb
+LowCardinality(String)	123_bb	3	123_a
+LowCardinality(String)	123_	1	123_bb
+LowCardinality(String)	123_a	2	123_
 LowCardinality(String)	123_ccc	4	123_ccc
 LowCardinality(String)	123_a	2	123_dddd
 LowCardinality(String)	123_bb	3	
@@ -11,9 +11,9 @@ LowCardinality(String)	123_dddd	5
 -
 LowCardinality(Nullable(String))	123_a	3	\N
 LowCardinality(Nullable(String))	\N	0	
-LowCardinality(Nullable(String))	123_bb	4	123_
-LowCardinality(Nullable(String))	123_	2	123_a
-LowCardinality(Nullable(String))	123_a	3	123_bb
+LowCardinality(Nullable(String))	123_bb	4	123_a
+LowCardinality(Nullable(String))	123_	2	123_bb
+LowCardinality(Nullable(String))	123_a	3	123_
 LowCardinality(Nullable(String))	\N	0	123_ccc
 LowCardinality(Nullable(String))	123_ccc	5	123_dddd
 LowCardinality(Nullable(String))	123_a	3	\N

tests/queries/0_stateless/03560_low_cardinality_keys_filter.reference

@@ -0,0 +1,2 @@
+
+ok

tests/queries/0_stateless/03560_low_cardinality_keys_filter.sql

@@ -0,0 +1,15 @@
+DROP TABLE IF EXISTS test;
+
+CREATE TABLE test
+(
+    s LowCardinality(String),
+    client_name String,
+) ENGINE = MergeTree ORDER BY ();
+
+INSERT INTO test
+SELECT number < 8000 ? 'ok' : 'fail' AS s,
+       number < 8000 ? 'client1' : 'client2' FROM numbers(20000);
+
+SELECT DISTINCT lowCardinalityKeys(s) FROM test PREWHERE client_name = 'client1' ORDER BY ALL;
+
+DROP TABLE test;