Unary predicates

Author: DerekStride

grammar.js

@@ -1356,10 +1356,13 @@ module.exports = grammar({
       $.select_expression,
     ),
 
-    where_expression: $ => seq(
-      $._expression,
+    where_expression: $ => choice(
+      $.predicate,
+      alias($._field_predicate, $.predicate),
     ),
 
+    _field_predicate: $ => field('operand', $.field),
+
     predicate: $ => choice(
       ...[
         ['=', 'binary_relation'],

src/grammar.json

@@ -5541,14 +5541,31 @@
       ]
     },
     "where_expression": {
-      "type": "SEQ",
+      "type": "CHOICE",
       "members": [
         {
           "type": "SYMBOL",
-          "name": "_expression"
+          "name": "predicate"
+        },
+        {
+          "type": "ALIAS",
+          "content": {
+            "type": "SYMBOL",
+            "name": "_field_predicate"
+          },
+          "named": true,
+          "value": "predicate"
         }
       ]
     },
+    "_field_predicate": {
+      "type": "FIELD",
+      "name": "operand",
+      "content": {
+        "type": "SYMBOL",
+        "name": "field"
+      }
+    },
     "predicate": {
       "type": "CHOICE",
       "members": [

src/node-types.json

@@ -2943,6 +2943,16 @@
           }
         ]
       },
+      "operand": {
+        "multiple": false,
+        "required": false,
+        "types": [
+          {
+            "type": "field",
+            "named": true
+          }
+        ]
+      },
       "operator": {
         "multiple": true,
         "required": false,
@@ -3792,53 +3802,9 @@
       "multiple": false,
       "required": true,
       "types": [
-        {
-          "type": "binary_expression",
-          "named": true
-        },
-        {
-          "type": "case",
-          "named": true
-        },
-        {
-          "type": "cast",
-          "named": true
-        },
-        {
-          "type": "count",
-          "named": true
-        },
-        {
-          "type": "field",
-          "named": true
-        },
-        {
-          "type": "invocation",
-          "named": true
-        },
-        {
-          "type": "list",
-          "named": true
-        },
-        {
-          "type": "literal",
-          "named": true
-        },
-        {
-          "type": "parameter",
-          "named": true
-        },
         {
           "type": "predicate",
           "named": true
-        },
-        {
-          "type": "subquery",
-          "named": true
-        },
-        {
-          "type": "window_function",
-          "named": true
         }
       ]
     }