fix: fix postgresql support (#606)

* fix postgresql support

fixes #517

* fix: fix pg support

* chore: delete useless code

---------

Co-authored-by: JustSong <songquanpeng@foxmail.com>

model/user.go

@@ -266,7 +266,12 @@ func GetUserEmail(id int) (email string, err error) {
 }
 
 func GetUserGroup(id int) (group string, err error) {
-	err = DB.Model(&User{}).Where("id = ?", id).Select("`group`").Find(&group).Error
+	groupCol := "`group`"
+	if common.UsingPostgreSQL {
+		groupCol = `"group"`
+	}
+
+	err = DB.Model(&User{}).Where("id = ?", id).Select(groupCol).Find(&group).Error
 	return group, err
 }