From 5ab362a303725368ee1f9db26179b37f39f62fad Mon Sep 17 00:00:00 2001
From: Nikolai Kochetov <nik-kochetov@yandex-team.ru>
Date: Wed, 9 Jan 2019 17:47:51 +0300
Subject: [PATCH] Fix distinct by single LowCardinality numeric column.

---
 dbms/src/Columns/ColumnLowCardinality.h       |   2 +-
 dbms/src/Interpreters/SetVariants.cpp         |   2 +-
 ...low_cardinality_distinct_numeric.reference | 123 ++++++++++++++++++
 ...00800_low_cardinality_distinct_numeric.sql |   7 +
 4 files changed, 132 insertions(+), 2 deletions(-)
 create mode 100644 dbms/tests/queries/0_stateless/00800_low_cardinality_distinct_numeric.reference
 create mode 100644 dbms/tests/queries/0_stateless/00800_low_cardinality_distinct_numeric.sql

diff --git a/dbms/src/Columns/ColumnLowCardinality.h b/dbms/src/Columns/ColumnLowCardinality.h
index bfca6e41123..34a3db8589e 100644
--- a/dbms/src/Columns/ColumnLowCardinality.h
+++ b/dbms/src/Columns/ColumnLowCardinality.h
@@ -133,7 +133,7 @@ public:
     }
 
     bool valuesHaveFixedSize() const override { return getDictionary().valuesHaveFixedSize(); }
-    bool isFixedAndContiguous() const override { return getDictionary().isFixedAndContiguous(); }
+    bool isFixedAndContiguous() const override { return false; }
     size_t sizeOfValueIfFixed() const override { return getDictionary().sizeOfValueIfFixed(); }
     bool isNumeric() const override { return getDictionary().isNumeric(); }
     bool lowCardinality() const override { return true; }
diff --git a/dbms/src/Interpreters/SetVariants.cpp b/dbms/src/Interpreters/SetVariants.cpp
index f0d9bbb2af8..6f457ed0bed 100644
--- a/dbms/src/Interpreters/SetVariants.cpp
+++ b/dbms/src/Interpreters/SetVariants.cpp
@@ -137,7 +137,7 @@ typename SetVariantsTemplate<Variant>::Type SetVariantsTemplate<Variant>::choose
     }
 
     /// If there is one numeric key that fits into 64 bits
-    if (keys_size == 1 && nested_key_columns[0]->isNumeric())
+    if (keys_size == 1 && nested_key_columns[0]->isNumeric() && !nested_key_columns[0]->lowCardinality())
     {
         size_t size_of_field = nested_key_columns[0]->sizeOfValueIfFixed();
         if (size_of_field == 1)
diff --git a/dbms/tests/queries/0_stateless/00800_low_cardinality_distinct_numeric.reference b/dbms/tests/queries/0_stateless/00800_low_cardinality_distinct_numeric.reference
new file mode 100644
index 00000000000..a39df1e16c0
--- /dev/null
+++ b/dbms/tests/queries/0_stateless/00800_low_cardinality_distinct_numeric.reference
@@ -0,0 +1,123 @@
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diff --git a/dbms/tests/queries/0_stateless/00800_low_cardinality_distinct_numeric.sql b/dbms/tests/queries/0_stateless/00800_low_cardinality_distinct_numeric.sql
new file mode 100644
index 00000000000..d3ba9138a8f
--- /dev/null
+++ b/dbms/tests/queries/0_stateless/00800_low_cardinality_distinct_numeric.sql
@@ -0,0 +1,7 @@
+set allow_experimental_low_cardinality_type = 1;
+drop table if exists test.lc;
+create table test.lc (val LowCardinality(UInt64)) engine = MergeTree order by val;
+insert into test.lc select number % 123 from system.numbers limit 100000;
+select distinct(val) from test.lc order by val;
+drop table if exists test.lc;
+