exec: Fix NULL expression handling in CASE and AND operators

This change fixes the CASE and AND operators when nulls were used as
expressions, which caused different errors than nulls existing as data
within the batches. Additionally, this change increases the safety of
the vectorized engine by disallowing the engine to plan
constNullOperators without knowing the "type" of the null to avoid
having the same panic arise. To get around this, when the "type" of the
null is known, a constNullOperator with a known type can be planned.
This is a temporary fix for the release. To be properly fixed, datum
nulls need to be aware of their type post typechecking, instead of being
"unknown".

Release justification: This PR fixes known panics within the vectorized engine.

Fixes #40526.

Release note: None

pkg/sql/colexec/const_test.go

@@ -55,7 +55,7 @@ func TestConstNull(t *testing.T) {
 	for _, tc := range tcs {
 		runTestsWithTyps(t, []tuples{tc.tuples}, []coltypes.T{coltypes.Int64}, tc.expected, orderedVerifier, []int{0, 1},
 			func(input []Operator) (Operator, error) {
-				return NewConstNullOp(input[0], 1), nil
+				return NewConstNullOp(input[0], 1, coltypes.Int64), nil
 			})
 	}
 }

pkg/sql/colexec/const_tmpl.go

@@ -111,16 +111,24 @@ func (c const_TYPEOp) Next(ctx context.Context) coldata.Batch {
 
 // NewConstNullOp creates a new operator that produces a constant (untyped) NULL
 // value at index outputIdx.
-func NewConstNullOp(input Operator, outputIdx int) Operator {
+func NewConstNullOp(input Operator, outputIdx int, typ coltypes.T) Operator {
 	return &constNullOp{
 		OneInputNode: NewOneInputNode(input),
 		outputIdx:    outputIdx,
+		typ:          typ,
 	}
 }
 
 type constNullOp struct {
 	OneInputNode
 	outputIdx int
+	typ       coltypes.T
+}
+
+var _ StaticMemoryOperator = &constNullOp{}
+
+func (c constNullOp) EstimateStaticMemoryUsage() int {
+	return EstimateBatchSizeBytes([]coltypes.T{c.typ}, coldata.BatchSize)
 }
 
 func (c constNullOp) Init() {
@@ -130,9 +138,11 @@ func (c constNullOp) Init() {
 func (c constNullOp) Next(ctx context.Context) coldata.Batch {
 	batch := c.input.Next(ctx)
 	n := batch.Length()
+
 	if batch.Width() == c.outputIdx {
-		batch.AppendCol(coltypes.Int8)
+		batch.AppendCol(c.typ)
 	}
+
 	if n == 0 {
 		return batch
 	}

pkg/sql/colflow/execplan.go

@@ -917,6 +917,10 @@ func planSelectionOperators(
 		op, resultIdx, ct, memUsed, err = planProjectionOperators(ctx, expr, columnTypes, input)
 		op = colexec.NewBoolVecToSelOp(op, resultIdx)
 		return op, resultIdx, ct, memUsed, err
+	case *tree.CaseExpr:
+		op, resultIdx, ct, memUsed, err = planProjectionOperators(ctx, expr, columnTypes, input)
+		op = colexec.NewBoolVecToSelOp(op, resultIdx)
+		return op, resultIdx, ct, memUsed, err
 	case *tree.ComparisonExpr:
 		cmpOp := t.Operator
 		leftOp, leftIdx, ct, memUsageLeft, err := planProjectionOperators(ctx, t.TypedLeft(), columnTypes, input)
@@ -955,6 +959,26 @@ func planSelectionOperators(
 	}
 }
 
+// planTypedMaybeNullProjectionOperators is used to plan projection operators, but is able to
+// plan constNullOperators in the case that we know the "type" of the null. It is currently
+// unsafe to plan a constNullOperator when we don't know the type of the null.
+func planTypedMaybeNullProjectionOperators(
+	ctx *tree.EvalContext,
+	expr tree.TypedExpr,
+	exprTyp *types.T,
+	columnTypes []types.T,
+	input colexec.Operator,
+) (op colexec.Operator, resultIdx int, ct []types.T, memUsed int, err error) {
+	if expr == tree.DNull {
+		resultIdx = len(columnTypes)
+		op = colexec.NewConstNullOp(input, resultIdx, typeconv.FromColumnType(exprTyp))
+		ct = append(columnTypes, *exprTyp)
+		memUsed = op.(colexec.StaticMemoryOperator).EstimateStaticMemoryUsage()
+		return op, resultIdx, ct, memUsed, nil
+	}
+	return planProjectionOperators(ctx, expr, columnTypes, input)
+}
+
 // planProjectionOperators plans a chain of operators to execute the provided
 // expression. It returns the tail of the chain, as well as the column index
 // of the expression's result (if any, otherwise -1) and the column types of the
@@ -972,7 +996,15 @@ func planProjectionOperators(
 		return planProjectionExpr(ctx, t.Operator, t.ResolvedType(), t.TypedLeft(), t.TypedRight(), columnTypes, input)
 	case *tree.CastExpr:
 		expr := t.Expr.(tree.TypedExpr)
-		op, resultIdx, ct, memUsed, err = planProjectionOperators(ctx, expr, columnTypes, input)
+		// If the expression is NULL, we use planTypedMaybeNullProjectionOperators instead of planProjectionOperators
+		// because we can say that the type of the NULL is the type that we are casting to, rather than unknown.
+		// We can't use planProjectionOperators because it will reject planning a constNullOp without knowing
+		// the post typechecking "type" of the NULL.
+		if expr.ResolvedType() == types.Unknown {
+			op, resultIdx, ct, memUsed, err = planTypedMaybeNullProjectionOperators(ctx, expr, t.Type, columnTypes, input)
+		} else {
+			op, resultIdx, ct, memUsed, err = planProjectionOperators(ctx, expr, columnTypes, input)
+		}
 		if err != nil {
 			return nil, 0, nil, 0, err
 		}
@@ -1013,7 +1045,7 @@ func planProjectionOperators(
 		resultIdx = len(ct)
 		ct = append(ct, *datumType)
 		if datumType.Family() == types.UnknownFamily {
-			return colexec.NewConstNullOp(input, resultIdx), resultIdx, ct, memUsed, nil
+			return nil, resultIdx, ct, memUsed, errors.New("cannot plan null type unknown")
 		}
 		typ := typeconv.FromColumnType(datumType)
 		constVal, err := typeconv.GetDatumToPhysicalFn(datumType)(t)
@@ -1051,17 +1083,17 @@ func planProjectionOperators(
 			// results of the WHEN into a single output vector, assembling the final
 			// result of the case projection.
 			var whenMemUsed, thenMemUsed int
-			caseOps[i], resultIdx, ct, whenMemUsed, err = planProjectionOperators(
-				ctx, when.Cond.(tree.TypedExpr), ct, buffer)
+			caseOps[i], resultIdx, ct, whenMemUsed, err = planTypedMaybeNullProjectionOperators(
+				ctx, when.Cond.(tree.TypedExpr), t.ResolvedType(), ct, buffer)
 			if err != nil {
 				return nil, resultIdx, ct, 0, err
 			}
 			// Transform the booleans to a selection vector.
 			caseOps[i] = colexec.NewBoolVecToSelOp(caseOps[i], resultIdx)
 
 			// Run the "then" clause on those tuples that were selected.
-			caseOps[i], thenIdxs[i], ct, thenMemUsed, err = planProjectionOperators(ctx, when.Val.(tree.TypedExpr), ct,
-				caseOps[i])
+			caseOps[i], thenIdxs[i], ct, thenMemUsed, err = planTypedMaybeNullProjectionOperators(
+				ctx, when.Val.(tree.TypedExpr), t.ResolvedType(), ct, caseOps[i])
 			if err != nil {
 				return nil, resultIdx, ct, 0, err
 			}
@@ -1075,8 +1107,8 @@ func planProjectionOperators(
 			// If there's no ELSE arm, we write NULLs.
 			elseExpr = tree.DNull
 		}
-		elseOp, thenIdxs[len(t.Whens)], ct, elseMem, err = planProjectionOperators(
-			ctx, elseExpr.(tree.TypedExpr), ct, buffer)
+		elseOp, thenIdxs[len(t.Whens)], ct, elseMem, err = planTypedMaybeNullProjectionOperators(
+			ctx, elseExpr.(tree.TypedExpr), t.ResolvedType(), ct, buffer)
 		if err != nil {
 			return nil, resultIdx, ct, 0, err
 		}
@@ -1088,11 +1120,11 @@ func planProjectionOperators(
 	case *tree.AndExpr:
 		var leftOp, rightOp colexec.Operator
 		var leftIdx, rightIdx, lMemUsed, rMemUsed int
-		leftOp, leftIdx, ct, lMemUsed, err = planProjectionOperators(ctx, t.TypedLeft(), columnTypes, input)
+		leftOp, leftIdx, ct, lMemUsed, err = planTypedMaybeNullProjectionOperators(ctx, t.TypedLeft(), types.Bool, columnTypes, input)
 		if err != nil {
 			return nil, resultIdx, ct, 0, err
 		}
-		rightOp, rightIdx, ct, rMemUsed, err = planProjectionOperators(ctx, t.TypedRight(), ct, leftOp)
+		rightOp, rightIdx, ct, rMemUsed, err = planTypedMaybeNullProjectionOperators(ctx, t.TypedRight(), types.Bool, ct, leftOp)
 		if err != nil {
 			return nil, resultIdx, ct, 0, err
 		}

pkg/sql/logictest/testdata/logic_test/vectorize

@@ -862,3 +862,37 @@ SELECT CASE WHEN a <= b THEN 1 ELSE 2 END
   FROM t1
  WHERE (a > b - 2 AND a < b + 2) OR (c > a AND c < b)
 ----
+
+# Regression tests for NULL expression handling.
+statement ok
+CREATE TABLE t_case_null (x INT)
+
+statement ok
+INSERT INTO t_case_null VALUES (0)
+
+query I
+SELECT CASE WHEN x = 0 THEN 0 ELSE NULL END FROM t_case_null
+----
+0
+
+query I
+SELECT CASE WHEN x = 0 THEN NULL ELSE 0 END FROM t_case_null
+----
+NULL
+
+query I
+SELECT CASE WHEN x = 1 THEN 1 ELSE NULL END FROM t_case_null
+----
+NULL
+
+query I
+SELECT * FROM t_case_null WHERE NULL AND NULL
+----
+
+query I
+SELECT * FROM t_case_null WHERE NULL AND x = 0
+----
+
+query I
+SELECT * FROM t_case_null WHERE x = 0 AND NULL
+----