colexec: fixed nullableArgs projection operators

Previously, the projection operators for binary or comparison expressions
directly copy nulls into the output without performing the actual projection
whenever either argument was null. This is incorrect because some function
operators can handle null arguments, and we want the actual projection result
instead. Since currently the only projection operator that needs `nullableArgs
== true`
behaviour is `ConcatDatumDatum`, this PR fixed this by only adding a
boolean field `nullableArgs` to operators with `Datum`, `Datum`. If we later
introduce another projection operation that has nullableArgs == true, we should
update code accordingly.

Fixes: cockroachdb#83091

Release note (bug fix): Fixed a bug in projection operators that gave output of
nulls when the expression can actually handle null arguments and may result in
a non-null output. Note that if we later
introduce another projection operation that has nullableArgs == true, we should
update code accordingly.

pkg/sql/colexec/colbuilder/execplan.go

@@ -1995,7 +1995,7 @@ func planProjectionOperators(
 		}
 		return planProjectionExpr(
 			ctx, evalCtx, t.Operator, t.ResolvedType(), t.TypedLeft(), t.TypedRight(),
-			columnTypes, input, acc, factory, t.Op.EvalOp, nil /* cmpExpr */, releasables,
+			columnTypes, input, acc, factory, t.Op.EvalOp, nil /* cmpExpr */, releasables, t.Op.NullableArgs,
 		)
 	case *tree.CaseExpr:
 		allocator := colmem.NewAllocator(ctx, acc, factory)
@@ -2147,7 +2147,7 @@ func planProjectionOperators(
 	case *tree.ComparisonExpr:
 		return planProjectionExpr(
 			ctx, evalCtx, t.Operator, t.ResolvedType(), t.TypedLeft(), t.TypedRight(),
-			columnTypes, input, acc, factory, nil /* binFn */, t, releasables,
+			columnTypes, input, acc, factory, nil /* binFn */, t, releasables, t.Op.NullableArgs,
 		)
 	case tree.Datum:
 		op, err = projectDatum(t)
@@ -2314,6 +2314,7 @@ func planProjectionExpr(
 	binOp tree.BinaryEvalOp,
 	cmpExpr *tree.ComparisonExpr,
 	releasables *[]execreleasable.Releasable,
+	nullableArgs bool,
 ) (op colexecop.Operator, resultIdx int, typs []*types.T, err error) {
 	if err := checkSupportedProjectionExpr(left, right); err != nil {
 		return nil, resultIdx, typs, err
@@ -2350,7 +2351,7 @@ func planProjectionExpr(
 		// appended to the input batch.
 		op, err = colexecprojconst.GetProjectionLConstOperator(
 			allocator, typs, left.ResolvedType(), outputType, projOp, input,
-			rightIdx, lConstArg, resultIdx, evalCtx, binOp, cmpExpr,
+			rightIdx, lConstArg, resultIdx, evalCtx, binOp, cmpExpr, nullableArgs,
 		)
 	} else {
 		var leftIdx int
@@ -2427,7 +2428,7 @@ func planProjectionExpr(
 				// all other projection operators.
 				op, err = colexecprojconst.GetProjectionRConstOperator(
 					allocator, typs, right.ResolvedType(), outputType, projOp,
-					input, leftIdx, rConstArg, resultIdx, evalCtx, binOp, cmpExpr,
+					input, leftIdx, rConstArg, resultIdx, evalCtx, binOp, cmpExpr, nullableArgs,
 				)
 			}
 		} else {
@@ -2442,7 +2443,7 @@ func planProjectionExpr(
 			resultIdx = len(typs)
 			op, err = colexecproj.GetProjectionOperator(
 				allocator, typs, outputType, projOp, input, leftIdx, rightIdx,
-				resultIdx, evalCtx, binOp, cmpExpr,
+				resultIdx, evalCtx, binOp, cmpExpr, nullableArgs,
 			)
 		}
 	}