How to LEFT JOIN two tables in Go using squirrel and handle nullable fields

I am quite new to Go, and I'm working on a project in Go where I'm using squirrel for SQL queries. I have two tables, User and UserLocation, and I need to do a LEFT JOIN between them. Here are my structs:

type User struct {
	Slug                string               `json:"slug" db:"slug"`
	Name                string               `json:"name" db:"name"`
	Label               null.String          `json:"label" db:"label"`
	*UserLocation
}

type UserLocation struct {
	Id            string      `json:"uuid" db:"id"`
	UserSlug      string      `json:"user_slug" db:"user_slug"`
	Latitude      float64     `json:"lat" db:"latitude"`
	Longitude     float64     `json:"lng" db:"longitude"`
}

The UserSlug field in the UserLocation table is a foreign key field that links to the User table's Slug field.

I'm trying to create a LEFT JOIN query that will return the User data along with any UserLocation data, if available. Here is the output format I need:

If the UserSlug is found in the UserLocation table, return the whole User JSON with a nested object for the location found:

{
    slug: "user_slug",
    name: "user name",
    label: "user label",
    location: {
        id: "some-uuid",
        user_slug: "user_slug",
        latitude: 0.123,
        longitude: 123.0
    }
}

However, if the UserSlug is not found in UserLocation, I want the result to not contain the location key at all:

{
    slug: "user_slug",
    name: "user name",
    label: "user label"
}

I am trying to accomplish this with something like this:

import (
	"context"
	"database/sql"
	"strings"
	"time"

	"github.com/lib/pq"

	sq "github.com/Masterminds/squirrel"
	"github.com/pkg/errors"
)

type User struct {
	Slug                string               `json:"slug" db:"slug"`
	Name                string               `json:"name" db:"name"`
	Label               null.String          `json:"label" db:"label"`
	*UserLocation
}

type UserLocation struct {
Id            string      `json:"uuid" db:"id"`
UserSlug      string      `json:"user_slug" db:"user_slug"`
Latitude      float64     `json:"lat" db:"latitude"`
Longitude     float64     `json:"lng" db:"longitude"`
}

type UserListResponse struct {
	Users []User `json:"users"`
}

func (p *Postgres) ListUsers(
	ctx context.Context,
	r UserListRequest,
) (UserListResponse, error) {
	var response UserListResponse
	selectColumns := append(tableUserColumns, tableUserLocationColumns)

	qb := sq.Select(selectColumns...).
		From(tableUser)

	qb = qb.LeftJoin(tableUserLocation + " ON " +
		tableColumn(tableUser, columnUserSlug) + " = " + (tableColumn(tableUserLocation, columnUserLocationSlug)))

	q, args, err := qb.
		ToSql()

	if err != nil {
		return response, errors.Wrap(err, "select all query q parsing")
	}

	err = p.db.SelectContext(ctx, &Users, q, args...)
	if err != nil {
		return response, errors.Wrap(err, "select all query execution")
	}

	return storyapi.UserListResponse{
		Users:         Users
	}, nil
}

but I keep getting the following error:

"select all query execution: missing destination name id in *[]User"

How can I do the LEFT JOIN in a way that allows me to ignore the nested object if a match is not found in UserLocations?

I don't know about squirrels so will give you one answer that when you don't want to send fields which are empty you can just put omitempty in the json tag of that field in struct like this

type User struct {
  Slug                string               `json:"slug" db:"slug"`
  Name                string               `json:"name" db:"name"`
  Label               null.String          `json:"label" db:"label"`
  Location            *UserLocation        `json:"location,omitempty"`
}

type UserLocation struct {
  Id            string      `json:"uuid" db:"id"`
  UserSlug      string      `json:"user_slug" db:"user_slug"`
  Latitude      float64     `json:"lat" db:"latitude"`
  Longitude     float64     `json:"lng" db:"longitude"`
}

Now for the problem you are facing with your query not working is that your User struct does not have field id which is in database and it is trying to find this field in your struct.

So my solution for that is if you want to send the response you have mentioned like this

{
    slug: "user_slug",
    name: "user name",
    label: "user label",
    location: {
        id: "some-uuid",
        user_slug: "user_slug",
        latitude: 0.123,
        longitude: 123.0
    }
}

what you have to do is don't do the left join because you can't map the Left join results to the struct which is not identical to database query result so you have to fire separate queries in loop based on the foreign key like this
note: it's not the perfect code and it is just to explain the logic and it may have error(not syntax)

var users []User
resultUser:=db.Query("Select * from user_table")
for resultUser.Next() {
  var user User
  _:=resultUser.ParseToStruct(&user)
  resultLocation:=db.Query("Select * From user_location_table where user_slug=?",user.Slug)
  //if you have multiple locations do it in loop and also change struct accordingly to handle array of locations
  if resultLocation.Next(){
	  var userLocation UserLocation
	  resultLocation.ParseToStruct(&userLocation)
	  //in case of loop user.Location=append(user.Location,&userLocation)
	  user.Location=&userLocation
  }
  users=append(users,user)
}

return users

Although i know this is very bad way but i have one more solution in case you have single location for single user

Just make a new custome struct like this which is identicle to join query response

 type UserJoinuserLocation struct{
      //User Details
      UserId              string               `db:"userId"`
      Slug                string               `db:"slug"`
      Name                string               `db:"name"`
      Label               null.String          `db:"label"`
      
      //User Location Details
      userLocationId string      `db:"userLocationId"`
      UserSlug       string      `db:"user_slug"`
      Latitude       float64     `db:"latitude"`
      Longitude      float64     `db:"longitude"`
   }

Make sure you have unique fields and if you want to change the field name then also change it in db tag and don't forget to put an alias for that name in sql query.
and then you can easily parse query response to your custome struct and then map that struct to your original struct and then send the response