Merge pull request ClickHouse#92434 from ClickHouse/backport/25.8/92351

Backport ClickHouse#92351 to 25.8: Fix logical error caused by `Nothing` type in `caseWithExpression` function

Author: clickhouse-gh[bot]

src/Functions/caseWithExpression.cpp

@@ -29,7 +29,6 @@ class FunctionCaseWithExpression : public IFunction
     bool isVariadic() const override { return true; }
     bool useDefaultImplementationForConstants() const override { return false; }
     bool useDefaultImplementationForNulls() const override { return false; }
-    bool useDefaultImplementationForNothing() const override { return false; }
     bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
     size_t getNumberOfArguments() const override { return 0; }
     String getName() const override { return name; }
@@ -62,14 +61,6 @@ class FunctionCaseWithExpression : public IFunction
     /// Helper function to implement CASE WHEN equality semantics where NULL = NULL is true
     ColumnPtr caseWhenEquals(const ColumnWithTypeAndName & expr, const ColumnWithTypeAndName & when_value, size_t input_rows_count) const
     {
-        // handle Nothing type - it's an empty type that can't contain any values
-        // if either argument is Nothing, the result should be an empty column
-        if (expr.type->onlyNull() || when_value.type->onlyNull())
-        {
-            // return a constant false column
-            return DataTypeUInt8().createColumnConst(input_rows_count, 0u);
-        }
-
         // for CASE WHEN semantics, NULL should match NULL
         // we need: if (isNull(expr)) then (isNull(when)) else if (isNull(when)) then 0 else (expr = when)
 

tests/queries/0_stateless/03390_non_constant_case.sql

@@ -59,4 +59,10 @@ SELECT caseWithExpression(
     materialize(NULL),
     NULL,
     NULL
-); -- { serverError ILLEGAL_COLUMN }
+); -- { serverError ILLEGAL_TYPE_OF_ARGUMENT }
+
+SELECT caseWithExpression('C', 'A', true, 'B', false); -- { serverError BAD_ARGUMENTS }
+
+SELECT caseWithExpression(1, assumeNotNull(materialize(NULL)), 1, 1); -- { serverError ILLEGAL_TYPE_OF_ARGUMENT }
+
+SELECT count() WHERE caseWithExpression(1, assumeNotNull(materialize(NULL)), 1, 1); -- { serverError ILLEGAL_TYPE_OF_COLUMN_FOR_FILTER }