Backport #54601 to 23.8: Fix serialization of ColumnDecimal

src/Columns/ColumnDecimal.cpp

@@ -80,7 +80,7 @@ StringRef ColumnDecimal<T>::serializeValueIntoArena(size_t n, Arena & arena, cha
         res.data = pos;
     }
     memcpy(pos, &data[n], sizeof(T));
-    return StringRef(pos, sizeof(T));
+    return res;
 }
 
 template <is_decimal T>

tests/queries/0_stateless/02875_fix_column_decimal_serialization.reference

@@ -0,0 +1 @@
+11	1	1	8	8	7367

tests/queries/0_stateless/02875_fix_column_decimal_serialization.sql

@@ -0,0 +1,17 @@
+CREATE TABLE max_length_alias_14053__fuzz_45
+(
+    `a` Date,
+    `b` Nullable(Decimal(76, 45)),
+    `c.d` Array(Nullable(DateTime64(3))),
+    `dcount` Int8 ALIAS length(c.d)
+)
+ENGINE = MergeTree
+PARTITION BY toMonday(a)
+ORDER BY (a, b)
+SETTINGS allow_nullable_key = 1, index_granularity = 8192;
+
+INSERT INTO max_length_alias_14053__fuzz_45 VALUES ('2020-10-06',7367,['2020-10-06','2020-10-06','2020-10-06','2020-10-06','2020-10-06']),('2020-10-06',7367,['2020-10-06','2020-10-06','2020-10-06']),('2020-10-06',7367,['2020-10-06','2020-10-06']),('2020-10-07',7367,['2020-10-07','2020-10-07','2020-10-07','2020-10-07','2020-10-07']),('2020-10-08',7367,['2020-10-08','2020-10-08','2020-10-08','2020-10-08']),('2020-10-11',7367,['2020-10-11','2020-10-11','2020-10-11','2020-10-11','2020-10-11','2020-10-11','2020-10-11','2020-10-11']),('2020-10-11',7367,['2020-10-11']),('2020-08-26',7367,['2020-08-26','2020-08-26']),('2020-08-28',7367,['2020-08-28','2020-08-28','2020-08-28']),('2020-08-29',7367,['2020-08-29']),('2020-09-22',7367,['2020-09-22','2020-09-22','2020-09-22','2020-09-22','2020-09-22','2020-09-22','2020-09-22']);
+
+SELECT count(), min(length(c.d)) AS minExpr, min(dcount) AS minAlias, max(length(c.d)) AS maxExpr, max(dcount) AS maxAlias, b FROM max_length_alias_14053__fuzz_45 GROUP BY b;
+
+DROP TABLE max_length_alias_14053__fuzz_45;