fix(model.count): distinct without any column generates invalid SQL (#11893)

lib/model.js

@@ -2031,7 +2031,9 @@ class Model {
       if (options.include) {
       if (options.include) {
         col = `${this.name}.${options.col || this.primaryKeyField}`;
         col = `${this.name}.${options.col || this.primaryKeyField}`;
       }
       }
-
+      if (options.distinct && col === '*') {
+        col = this.primaryKeyField;
+      }
       options.plain = !options.group;
       options.plain = !options.group;
       options.dataType = new DataTypes.INTEGER();
       options.dataType = new DataTypes.INTEGER();
       options.includeIgnoreAttributes = false;
       options.includeIgnoreAttributes = false;

test/integration/model/count.test.js

@@ -109,6 +109,21 @@ describe(Support.getTestDialectTeaser('Model'), () => {
         });
         });
     });
     });
 
 
+    it('should be able to specify NO column for COUNT() with DISTINCT', function() {
+      return this.User.bulkCreate([
+        { username: 'ember', age: 10 },
+        { username: 'angular', age: 20 },
+        { username: 'mithril', age: 10 }
+      ]).then(() => {
+        return this.User.count({
+          distinct: true
+        });
+      })
+        .then(count => {
+          expect(count).to.be.eql(3);
+        });
+    });
+
     it('should be able to use where clause on included models', function() {
     it('should be able to use where clause on included models', function() {
       const countOptions = {
       const countOptions = {
         col: 'username',
         col: 'username',