Merge pull request #59642 from ClickHouse/cherrypick/23.11/79d91294c6…

…27ce823ecdd3c2280627bfd2d4e54a

Cherry pick #59594 to 23.11: Fix incorrect result of arrayElement / map[] on empty value

src/Functions/array/arrayElement.cpp

@@ -277,8 +277,7 @@ struct ArrayElementStringImpl
         ColumnArray::Offset current_offset = 0;
         /// get the total result bytes at first, and reduce the cost of result_data.resize.
         size_t total_result_bytes = 0;
-        ColumnString::Chars zero_buf(1);
-        zero_buf.push_back(0);
+        ColumnString::Chars zero_buf(16, '\0'); /// Needs 15 extra bytes for memcpySmallAllowReadWriteOverflow15
         std::vector<std::pair<const ColumnString::Char *, UInt64>> selected_bufs;
         selected_bufs.reserve(size);
         for (size_t i = 0; i < size; ++i)
@@ -344,8 +343,7 @@ struct ArrayElementStringImpl
         size_t size = offsets.size();
         result_offsets.resize(size);
 
-        ColumnString::Chars zero_buf(1);
-        zero_buf.push_back(0);
+        ColumnString::Chars zero_buf(16, '\0'); /// Needs 15 extra bytes for memcpySmallAllowReadWriteOverflow15
         ColumnArray::Offset current_offset = 0;
         /// get the total result bytes at first, and reduce the cost of result_data.resize.
         size_t total_result_bytes = 0;

tests/queries/0_stateless/02983_empty_map.reference

@@ -0,0 +1,7 @@
+-- { echoOn }
+SELECT f1, f2['2'], count() FROM t1 GROUP BY 1,2 order by 1,2;
+1		1000111
+SELECT f1, f3['2'], count() FROM t1 GROUP BY 1,2 order by 1,2;
+1		1000111
+SELECT f1, f4[2], count() FROM t1 GROUP BY 1,2 order by 1,2;
+1	0	1000111

tests/queries/0_stateless/02983_empty_map.sql

@@ -0,0 +1,21 @@
+--https://github.com/ClickHouse/ClickHouse/issues/59402
+CREATE TABLE t1
+(
+    f1 Int32,
+    f2 Map(LowCardinality(String),LowCardinality(String)),
+    f3 Map(String,String),
+    f4 Map(Int32,Int32)
+)
+ENGINE=Memory AS
+SELECT 1 as f1,
+       map(number%2,number%10) as f2,
+       f2 as f3,
+       f2 as f4
+from numbers(1000111);
+
+SET max_block_size=10;
+
+-- { echoOn }
+SELECT f1, f2['2'], count() FROM t1 GROUP BY 1,2 order by 1,2;
+SELECT f1, f3['2'], count() FROM t1 GROUP BY 1,2 order by 1,2;
+SELECT f1, f4[2], count() FROM t1 GROUP BY 1,2 order by 1,2;