diff --git a/pkg/ql/ast_nodes.go b/pkg/ql/ast_nodes.go
index dd7b2382f..758389fd9 100644
--- a/pkg/ql/ast_nodes.go
+++ b/pkg/ql/ast_nodes.go
@@ -3,6 +3,7 @@ package ql
 import (
 	"fmt"
 	"github.com/Masterminds/squirrel"
+	"strings"
 )
 
 // SelectStatement represents a SQL SELECT statement.
@@ -65,6 +66,29 @@ type (
 	}
 )
 
+var (
+	operators = map[string]bool{
+		`=`:        true,
+		`!=`:       true,
+		`<`:        true,
+		`>`:        true,
+		`>=`:       true,
+		`<=`:       true,
+		`<>`:       true,
+		`+`:        true,
+		`-`:        true,
+		`*`:        true,
+		`/`:        true,
+		`AND`:      true,
+		`OR`:       true,
+		`XOR`:      true,
+		`NOT LIKE`: true,
+		`LIKE`:     true,
+		`IS`:       true,
+		`IS NOT`:   true,
+	}
+)
+
 func (n LNull) Validate() (err error) { return }
 func (n LNull) String() string        { return "NULL" }
 
@@ -83,8 +107,13 @@ func (n LString) String() string        { return fmt.Sprintf("%q", n.Value) }
 func (n LNumber) Validate() (err error) { return }
 func (n LNumber) String() string        { return n.Value }
 
-func (n Operator) Validate() (err error) { return }
-func (n Operator) String() string        { return n.Kind }
+func (n Operator) Validate() (err error) {
+	if !operators[strings.ToUpper(n.Kind)] {
+		return fmt.Errorf("unknown operator '%s'", n.Kind)
+	}
+	return
+}
+func (n Operator) String() string { return n.Kind }
 
 func (n Keyword) Validate() (err error) { return }
 func (n Keyword) String() string        { return n.Keyword }
@@ -98,7 +127,10 @@ func (n Function) String() string        { return fmt.Sprintf("%s(%s)", n.Name,
 func (n Ident) Validate() (err error) { return }
 func (n Ident) String() string        { return n.Value }
 
-func (n Column) Validate() (err error) { return }
+func (n Column) Validate() (err error) {
+	return n.Expr.Validate()
+}
+
 func (n Column) String() (out string) {
 	out = n.Expr.String()
 	if n.Alias != "" {
@@ -158,7 +190,15 @@ func (nn ASTSet) String() (out string) {
 	return
 }
 
-func (nn Columns) Validate() (err error) { return }
+func (nn Columns) Validate() (err error) {
+	for _, n := range nn {
+		if err = n.Validate(); err != nil {
+			return
+		}
+	}
+
+	return
+}
 func (nn Columns) String() (out string) {
 	for i, n := range nn {
 		if i > 0 {
diff --git a/pkg/ql/ast_parser_test.go b/pkg/ql/ast_parser_test.go
index 0362ce608..61f49c004 100644
--- a/pkg/ql/ast_parser_test.go
+++ b/pkg/ql/ast_parser_test.go
@@ -2,6 +2,7 @@ package ql
 
 import (
 	"fmt"
+	"github.com/stretchr/testify/require"
 	"reflect"
 	"testing"
 )
@@ -297,7 +298,7 @@ func TestAstParser_ColumnParser(t *testing.T) {
 	var tests = []struct {
 		in   string
 		cols Columns
-		err  error
+		err  string
 	}{
 		{
 			in: `a AS b`,
@@ -370,15 +371,43 @@ func TestAstParser_ColumnParser(t *testing.T) {
 				},
 			},
 		},
+		{
+			in: `-- - DATE_FORMAT(some_date, '%Y-%m-01')`,
+			cols: Columns{
+				Column{
+					Expr: ASTNodes{
+						Function{
+							Name: "DATE_FORMAT",
+							Arguments: ASTSet{
+								Ident{Value: "some_date"},
+								LString{Value: "%Y-%m-01"},
+							},
+						},
+					},
+				},
+			},
+			err: "unknown operator '-- -'",
+		},
 	}
 
-	p := NewParser()
-	for i, test := range tests {
-		if cols, err := p.ParseColumns(test.in); err != test.err {
-			t.Fatalf("%d. %s: error mismatch:\n  expected: %v\n        got: %v\n\n", i, test.in, test.err, err)
-		} else if test.err == nil && !reflect.DeepEqual(test.cols, cols) {
-			t.Errorf("%d. %s\n\ncols does not match:\n\nexpected: %#v\n     got: %#v\n\n", i, test.in, test.cols, cols)
-		}
+	for _, test := range tests {
+		t.Run(test.in, func(t *testing.T) {
+			var (
+				p   = NewParser()
+				req = require.New(t)
+			)
+
+			cols, err := p.ParseColumns(test.in)
+			if test.err == "" {
+				req.NoError(err)
+			} else {
+				req.Error(err, test.err)
+			}
+
+			if err == nil {
+				req.Equal(test.cols, cols)
+			}
+		})
 	}
 }
 
@@ -400,7 +429,6 @@ func TestAstParser_IdentModifier(t *testing.T) {
 			ident.Value = fmt.Sprintf("__wrap_%s_wrap__", ident.Value)
 			return ident, nil
 		}
-
 		if tree, err := p.ParseExpression(test.in); err != test.err {
 			t.Fatalf("%d. error mismatch:\n  expected: %v\n        got: %v\n\n", i, test.err, err)
 		} else if test.err == nil && test.out != tree.String() {