SQL null semantics for and, or, not

Closes #5465

compiler/kernel/filter.go

@@ -36,9 +36,8 @@ func (f *DeleteFilter) AsEvaluator() (expr.Evaluator, error) {
 		return nil, nil
 	}
 	// For a DeleteFilter Evaluator the pushdown gets wrapped in a unary !
-	// expression so we get all values that don't match. We also add a missing
-	// call so if the expression results in an error("missing") the value is
-	// kept.
+	// expression so we get all values that don't match. We also add an error
+	// and null check because we want to keep these values around.
 	return f.builder.compileExpr(&dag.BinaryExpr{
 		Kind: "BinaryExpr",
 		Op:   "or",
@@ -47,10 +46,11 @@ func (f *DeleteFilter) AsEvaluator() (expr.Evaluator, error) {
 			Op:      "!",
 			Operand: f.pushdown,
 		},
-		RHS: &dag.Call{
-			Kind: "Call",
-			Name: "missing",
-			Args: []dag.Expr{f.pushdown},
+		RHS: &dag.BinaryExpr{
+			Kind: "BinaryExpr",
+			Op:   "or",
+			LHS:  &dag.IsNullExpr{Kind: "IsNullExpr", Expr: f.pushdown},
+			RHS:  &dag.Call{Kind: "Call", Name: "is_error", Args: []dag.Expr{f.pushdown}},
 		},
 	})
 }

lake/pool.go

@@ -179,8 +179,7 @@ func filter(zctx *super.Context, ectx expr.Context, this super.Value, e expr.Eva
 	if e == nil {
 		return true
 	}
-	val, ok := expr.EvalBool(zctx, ectx, this, e)
-	return ok && val.Bool()
+	return expr.EvalBool(zctx, ectx, this, e).Ptr().AsBool()
 }
 
 type BranchTip struct {

runtime/sam/expr/agg.go

@@ -34,7 +34,7 @@ func (a *Aggregator) NewFunction() agg.Function {
 
 func (a *Aggregator) Apply(zctx *super.Context, ectx Context, f agg.Function, this super.Value) {
 	if a.where != nil {
-		if val, ok := EvalBool(zctx, ectx, this, a.where); !ok || !val.Bool() {
+		if val := EvalBool(zctx, ectx, this, a.where); !val.AsBool() {
 			// XXX Issue #3401: do something with "where" errors.
 			return
 		}

runtime/sam/expr/eval.go

@@ -34,14 +34,11 @@ func NewLogicalNot(zctx *super.Context, e Evaluator) *Not {
 }
 
 func (n *Not) Eval(ectx Context, this super.Value) super.Value {
-	val, ok := EvalBool(n.zctx, ectx, this, n.expr)
-	if !ok {
+	val := EvalBool(n.zctx, ectx, this, n.expr)
+	if val.IsError() || val.IsNull() {
 		return val
 	}
-	if val.Bool() {
-		return super.False
-	}
-	return super.True
+	return super.NewBool(!val.Bool())
 }
 
 type And struct {
@@ -64,54 +61,62 @@ func NewLogicalOr(zctx *super.Context, lhs, rhs Evaluator) *Or {
 	return &Or{zctx, lhs, rhs}
 }
 
-// EvalBool evaluates e with this and if the result is a Zed bool, returns the
-// result and true.  Otherwise, a Zed error (inclusive of missing) and false
-// are returned.
-func EvalBool(zctx *super.Context, ectx Context, this super.Value, e Evaluator) (super.Value, bool) {
+// EvalBool evaluates e with this and returns the result if it is a bool or error.
+// Otherwise, EvalBool returns an error.
+func EvalBool(zctx *super.Context, ectx Context, this super.Value, e Evaluator) super.Value {
 	val := e.Eval(ectx, this)
-	if super.TypeUnder(val.Type()) == super.TypeBool {
-		return val, true
-	}
-	if val.IsError() {
-		return val, false
+	if super.TypeUnder(val.Type()) == super.TypeBool || val.IsError() {
+		return val
 	}
-	return zctx.WrapError("not type bool", val), false
+	return zctx.WrapError("not type bool", val)
 }
 
 func (a *And) Eval(ectx Context, this super.Value) super.Value {
-	lhs, ok := EvalBool(a.zctx, ectx, this, a.lhs)
-	if !ok {
-		return lhs
-	}
-	if !lhs.Bool() {
+	lhs := EvalBool(a.zctx, ectx, this, a.lhs)
+	rhs := EvalBool(a.zctx, ectx, this, a.rhs)
+	if isfalse(lhs) || isfalse(rhs) {
+		// anything AND FALSE = FALSE
 		return super.False
 	}
-	rhs, ok := EvalBool(a.zctx, ectx, this, a.rhs)
-	if !ok {
+	// ERROR AND NULL = ERROR
+	// ERROR AND TRUE = ERROR
+	if lhs.IsError() {
+		return lhs
+	}
+	if rhs.IsError() {
 		return rhs
 	}
-	if !rhs.Bool() {
-		return super.False
+	if lhs.IsNull() || rhs.IsNull() {
+		// NULL AND TRUE = NULL
+		return super.NullBool
 	}
 	return super.True
 }
 
+func isfalse(val super.Value) bool {
+	return val.Type().ID() == super.IDBool && !val.IsNull() && !val.Bool()
+}
+
 func (o *Or) Eval(ectx Context, this super.Value) super.Value {
-	lhs, ok := EvalBool(o.zctx, ectx, this, o.lhs)
-	if ok && lhs.Bool() {
+	lhs := EvalBool(o.zctx, ectx, this, o.lhs)
+	rhs := EvalBool(o.zctx, ectx, this, o.rhs)
+	if lhs.AsBool() || rhs.AsBool() {
+		// anything OR TRUE = TRUE
 		return super.True
 	}
-	if lhs.IsError() && !lhs.IsMissing() {
+	if lhs.IsNull() || rhs.IsNull() {
+		// NULL OR FALSE = NULL
+		// NULL OR ERROR = NULL
+		return super.NullBool
+	}
+	// ERROR OR FALSE = ERROR
+	if lhs.IsError() {
 		return lhs
 	}
-	rhs, ok := EvalBool(o.zctx, ectx, this, o.rhs)
-	if ok {
-		if rhs.Bool() {
-			return super.True
-		}
-		return super.False
+	if rhs.IsError() {
+		return rhs
 	}
-	return rhs
+	return super.False
 }
 
 type In struct {

runtime/sam/expr/filter.go

@@ -254,8 +254,8 @@ func NewFilterApplier(zctx *super.Context, e Evaluator) Evaluator {
 }
 
 func (f *filterApplier) Eval(ectx Context, this super.Value) super.Value {
-	val, ok := EvalBool(f.zctx, ectx, this, f.expr)
-	if ok {
+	val := EvalBool(f.zctx, ectx, this, f.expr)
+	if val.Type().ID() == super.IDBool {
 		if val.Bool() {
 			return this
 		}