Merge pull request #21327 from amosbird/hasequalvalue

IColunm::hasEqualValues()

src/Columns/ColumnAggregateFunction.h

@@ -198,6 +198,11 @@ public:
         throw Exception("Method compareColumn is not supported for ColumnAggregateFunction", ErrorCodes::NOT_IMPLEMENTED);
     }
 
+    bool hasEqualValues() const override
+    {
+        throw Exception("Method hasEqualValues is not supported for ColumnAggregateFunction", ErrorCodes::NOT_IMPLEMENTED);
+    }
+
     void getPermutation(bool reverse, size_t limit, int nan_direction_hint, Permutation & res) const override;
     void updatePermutation(bool reverse, size_t limit, int, Permutation & res, EqualRanges & equal_range) const override;
 

src/Columns/ColumnArray.cpp

@@ -370,6 +370,10 @@ void ColumnArray::compareColumn(const IColumn & rhs, size_t rhs_row_num,
                                         compare_results, direction, nan_direction_hint);
 }
 
+bool ColumnArray::hasEqualValues() const
+{
+    return hasEqualValuesImpl<ColumnArray>();
+}
 
 namespace
 {

src/Columns/ColumnArray.h

@@ -78,6 +78,7 @@ public:
                        PaddedPODArray<UInt64> * row_indexes, PaddedPODArray<Int8> & compare_results,
                        int direction, int nan_direction_hint) const override;
     int compareAtWithCollation(size_t n, size_t m, const IColumn & rhs_, int nan_direction_hint, const Collator & collator) const override;
+    bool hasEqualValues() const override;
     void getPermutation(bool reverse, size_t limit, int nan_direction_hint, Permutation & res) const override;
     void updatePermutation(bool reverse, size_t limit, int nan_direction_hint, Permutation & res, EqualRanges & equal_range) const override;
     void getPermutationWithCollation(const Collator & collator, bool reverse, size_t limit, int nan_direction_hint, Permutation & res) const override;

src/Columns/ColumnCompressed.h

@@ -96,6 +96,10 @@ public:
     {
         throwMustBeDecompressed();
     }
+    bool hasEqualValues() const override
+    {
+        throwMustBeDecompressed();
+    }
     void getPermutation(bool, size_t, int, Permutation &) const override { throwMustBeDecompressed(); }
     void updatePermutation(bool, size_t, int, Permutation &, EqualRanges &) const override { throwMustBeDecompressed(); }
     ColumnPtr replicate(const Offsets &) const override { throwMustBeDecompressed(); }

src/Columns/ColumnConst.h

@@ -206,6 +206,8 @@ public:
                        PaddedPODArray<UInt64> * row_indexes, PaddedPODArray<Int8> & compare_results,
                        int direction, int nan_direction_hint) const override;
 
+    bool hasEqualValues() const override { return true; }
+
     MutableColumns scatter(ColumnIndex num_columns, const Selector & selector) const override;
 
     void gather(ColumnGathererStream &) override

src/Columns/ColumnDecimal.cpp

@@ -58,6 +58,12 @@ void ColumnDecimal<T>::compareColumn(const IColumn & rhs, size_t rhs_row_num,
                                                          compare_results, direction, nan_direction_hint);
 }
 
+template <typename T>
+bool ColumnDecimal<T>::hasEqualValues() const
+{
+    return this->template hasEqualValuesImpl<ColumnDecimal<T>>();
+}
+
 template <typename T>
 StringRef ColumnDecimal<T>::serializeValueIntoArena(size_t n, Arena & arena, char const *& begin) const
 {

src/Columns/ColumnDecimal.h

@@ -136,6 +136,7 @@ public:
     void compareColumn(const IColumn & rhs, size_t rhs_row_num,
                        PaddedPODArray<UInt64> * row_indexes, PaddedPODArray<Int8> & compare_results,
                        int direction, int nan_direction_hint) const override;
+    bool hasEqualValues() const override;
     void getPermutation(bool reverse, size_t limit, int nan_direction_hint, IColumn::Permutation & res) const override;
     void updatePermutation(bool reverse, size_t limit, int, IColumn::Permutation & res, EqualRanges& equal_range) const override;
 

src/Columns/ColumnFixedString.h

@@ -132,6 +132,11 @@ public:
                                                compare_results, direction, nan_direction_hint);
     }
 
+    bool hasEqualValues() const override
+    {
+        return hasEqualValuesImpl<ColumnFixedString>();
+    }
+
     void getPermutation(bool reverse, size_t limit, int nan_direction_hint, Permutation & res) const override;
 
     void updatePermutation(bool reverse, size_t limit, int nan_direction_hint, Permutation & res, EqualRanges & equal_range) const override;

src/Columns/ColumnFunction.h

@@ -128,6 +128,11 @@ public:
         throw Exception("compareColumn is not implemented for " + getName(), ErrorCodes::NOT_IMPLEMENTED);
     }
 
+    bool hasEqualValues() const override
+    {
+        throw Exception("hasEqualValues is not implemented for " + getName(), ErrorCodes::NOT_IMPLEMENTED);
+    }
+
     void getPermutation(bool, size_t, int, Permutation &) const override
     {
         throw Exception("getPermutation is not implemented for " + getName(), ErrorCodes::NOT_IMPLEMENTED);

src/Columns/ColumnLowCardinality.cpp

@@ -311,6 +311,13 @@ void ColumnLowCardinality::compareColumn(const IColumn & rhs, size_t rhs_row_num
             compare_results, direction, nan_direction_hint);
 }
 
+bool ColumnLowCardinality::hasEqualValues() const
+{
+    if (getDictionary().size() <= 1)
+        return true;
+    return getIndexes().hasEqualValues();
+}
+
 void ColumnLowCardinality::getPermutationImpl(bool reverse, size_t limit, int nan_direction_hint, Permutation & res, const Collator * collator) const
 {
     if (limit == 0)

src/Columns/ColumnLowCardinality.h

@@ -126,6 +126,8 @@ public:
 
     int compareAtWithCollation(size_t n, size_t m, const IColumn & rhs, int nan_direction_hint, const Collator &) const override;
 
+    bool hasEqualValues() const override;
+
     void getPermutation(bool reverse, size_t limit, int nan_direction_hint, Permutation & res) const override;
 
     void updatePermutation(bool reverse, size_t limit, int, IColumn::Permutation & res, EqualRanges & equal_range) const override;

src/Columns/ColumnMap.cpp

@@ -187,6 +187,11 @@ void ColumnMap::compareColumn(const IColumn & rhs, size_t rhs_row_num,
                                         compare_results, direction, nan_direction_hint);
 }
 
+bool ColumnMap::hasEqualValues() const
+{
+    return hasEqualValuesImpl<ColumnMap>();
+}
+
 void ColumnMap::getPermutation(bool reverse, size_t limit, int nan_direction_hint, Permutation & res) const
 {
     nested->getPermutation(reverse, limit, nan_direction_hint, res);

src/Columns/ColumnMap.h

@@ -72,6 +72,7 @@ public:
     void compareColumn(const IColumn & rhs, size_t rhs_row_num,
                        PaddedPODArray<UInt64> * row_indexes, PaddedPODArray<Int8> & compare_results,
                        int direction, int nan_direction_hint) const override;
+    bool hasEqualValues() const override;
     void getExtremes(Field & min, Field & max) const override;
     void getPermutation(bool reverse, size_t limit, int nan_direction_hint, Permutation & res) const override;
     void updatePermutation(bool reverse, size_t limit, int nan_direction_hint, IColumn::Permutation & res, EqualRanges & equal_range) const override;

src/Columns/ColumnNullable.cpp

@@ -271,6 +271,11 @@ void ColumnNullable::compareColumn(const IColumn & rhs, size_t rhs_row_num,
                                            compare_results, direction, nan_direction_hint);
 }
 
+bool ColumnNullable::hasEqualValues() const
+{
+    return hasEqualValuesImpl<ColumnNullable>();
+}
+
 void ColumnNullable::getPermutationImpl(bool reverse, size_t limit, int null_direction_hint, Permutation & res, const Collator * collator) const
 {
     /// Cannot pass limit because of unknown amount of NULLs.

src/Columns/ColumnNullable.h

@@ -94,6 +94,7 @@ public:
                        PaddedPODArray<UInt64> * row_indexes, PaddedPODArray<Int8> & compare_results,
                        int direction, int nan_direction_hint) const override;
     int compareAtWithCollation(size_t n, size_t m, const IColumn & rhs, int null_direction_hint, const Collator &) const override;
+    bool hasEqualValues() const override;
     void getPermutation(bool reverse, size_t limit, int null_direction_hint, Permutation & res) const override;
     void updatePermutation(bool reverse, size_t limit, int null_direction_hint, Permutation & res, EqualRanges & equal_range) const override;
     void getPermutationWithCollation(const Collator & collator, bool reverse, size_t limit, int null_direction_hint, Permutation & res) const override;

src/Columns/ColumnString.cpp

@@ -287,6 +287,11 @@ void ColumnString::compareColumn(
                                          compare_results, direction, nan_direction_hint);
 }
 
+bool ColumnString::hasEqualValues() const
+{
+    return hasEqualValuesImpl<ColumnString>();
+}
+
 template <bool positive>
 struct ColumnString::Cmp
 {

src/Columns/ColumnString.h

@@ -240,6 +240,8 @@ public:
                        PaddedPODArray<UInt64> * row_indexes, PaddedPODArray<Int8> & compare_results,
                        int direction, int nan_direction_hint) const override;
 
+    bool hasEqualValues() const override;
+
     /// Variant of compareAt for string comparison with respect of collation.
     int compareAtWithCollation(size_t n, size_t m, const IColumn & rhs_, int, const Collator & collator) const override;
 

src/Columns/ColumnTuple.cpp

@@ -312,6 +312,11 @@ int ColumnTuple::compareAtWithCollation(size_t n, size_t m, const IColumn & rhs,
     return compareAtImpl(n, m, rhs, nan_direction_hint, &collator);
 }
 
+bool ColumnTuple::hasEqualValues() const
+{
+    return hasEqualValuesImpl<ColumnTuple>();
+}
+
 template <bool positive>
 struct ColumnTuple::Less
 {

src/Columns/ColumnTuple.h

@@ -76,6 +76,7 @@ public:
                        PaddedPODArray<UInt64> * row_indexes, PaddedPODArray<Int8> & compare_results,
                        int direction, int nan_direction_hint) const override;
     int compareAtWithCollation(size_t n, size_t m, const IColumn & rhs, int nan_direction_hint, const Collator & collator) const override;
+    bool hasEqualValues() const override;
     void getExtremes(Field & min, Field & max) const override;
     void getPermutation(bool reverse, size_t limit, int nan_direction_hint, Permutation & res) const override;
     void updatePermutation(bool reverse, size_t limit, int nan_direction_hint, IColumn::Permutation & res, EqualRanges & equal_ranges) const override;

src/Columns/ColumnVector.h

@@ -205,6 +205,11 @@ public:
                                                     compare_results, direction, nan_direction_hint);
     }
 
+    bool hasEqualValues() const override
+    {
+        return this->template hasEqualValuesImpl<Self>();
+    }
+
     void getPermutation(bool reverse, size_t limit, int nan_direction_hint, IColumn::Permutation & res) const override;
 
     void updatePermutation(bool reverse, size_t limit, int nan_direction_hint, IColumn::Permutation & res, EqualRanges& equal_range) const override;

src/Columns/IColumn.h

@@ -266,6 +266,9 @@ public:
                                PaddedPODArray<UInt64> * row_indexes, PaddedPODArray<Int8> & compare_results,
                                int direction, int nan_direction_hint) const = 0;
 
+    /// Check if all elements in the column have equal values. Return true if column is empty.
+    virtual bool hasEqualValues() const = 0;
+
     /** Returns a permutation that sorts elements of this column,
       *  i.e. perm[i]-th element of source column should be i-th element of sorted column.
       * reverse - reverse ordering (acsending).
@@ -467,6 +470,9 @@ protected:
                          PaddedPODArray<UInt64> * row_indexes,
                          PaddedPODArray<Int8> & compare_results,
                          int direction, int nan_direction_hint) const;
+
+    template <typename Derived>
+    bool hasEqualValuesImpl() const;
 };
 
 using ColumnPtr = IColumn::Ptr;

src/Columns/IColumnDummy.h

@@ -40,6 +40,8 @@ public:
     {
     }
 
+    bool hasEqualValues() const override { return true; }
+
     Field operator[](size_t) const override { throw Exception("Cannot get value from " + getName(), ErrorCodes::NOT_IMPLEMENTED); }
     void get(size_t, Field &) const override { throw Exception("Cannot get value from " + getName(), ErrorCodes::NOT_IMPLEMENTED); }
     void insert(const Field &) override { throw Exception("Cannot insert element into " + getName(), ErrorCodes::NOT_IMPLEMENTED); }

src/Columns/IColumnImpl.h

@@ -127,4 +127,16 @@ void IColumn::doCompareColumn(const Derived & rhs, size_t rhs_row_num,
     }
 }
 
+template <typename Derived>
+bool IColumn::hasEqualValuesImpl() const
+{
+    size_t num_rows = size();
+    for (size_t i = 1; i < num_rows; ++i)
+    {
+        if (compareAt(i, 0, static_cast<const Derived &>(*this), false) != 0)
+            return false;
+    }
+    return true;
+}
+
 }

src/Columns/IColumnUnique.h

@@ -172,6 +172,11 @@ public:
     {
         throw Exception("Method compareColumn is not supported for ColumnUnique.", ErrorCodes::NOT_IMPLEMENTED);
     }
+
+    bool hasEqualValues() const override
+    {
+        throw Exception("Method hasEqualValues is not supported for ColumnUnique.", ErrorCodes::NOT_IMPLEMENTED);
+    }
 };
 
 using ColumnUniquePtr = IColumnUnique::ColumnUniquePtr;