Fix joinGet crash with LowCardinality types.

src/Functions/FunctionJoinGet.h

@@ -80,7 +80,7 @@ public:
     DataTypePtr getReturnType(const ColumnsWithTypeAndName &) const override { return {}; } // Not used
 
     bool useDefaultImplementationForNulls() const override { return false; }
-    bool useDefaultImplementationForLowCardinalityColumns() const override { return true; }
+    bool useDefaultImplementationForLowCardinalityColumns() const override { return false; }
 
     bool isVariadic() const override { return true; }
     size_t getNumberOfArguments() const override { return 0; }

tests/queries/0_stateless/01400_join_get_with_multi_keys.reference

 0.1
+0.1

tests/queries/0_stateless/01400_join_get_with_multi_keys.sql

@@ -6,4 +6,10 @@ INSERT INTO test_joinGet VALUES ('ab', '1', 0.1), ('ab', '2', 0.2), ('cd', '3',
 
 SELECT joinGet(test_joinGet, 'c', 'ab', '1');
 
+CREATE TABLE test_lc(a LowCardinality(String), b LowCardinality(String), c Float64) ENGINE = Join(any, left, a, b);
+
+INSERT INTO test_lc VALUES ('ab', '1', 0.1), ('ab', '2', 0.2), ('cd', '3', 0.3);
+
+SELECT joinGet(test_lc, 'c', 'ab', '1');
+
 DROP TABLE test_joinGet;