Issue Description

What are you doing?

I am trying to strongly type my application using Typescript and Sequelize. I have noticed the following behaviour of the findAndCountAll function.

1. When no group by is supplied it returns Promise<{ rows: M[]; count: number }>.
2. When group by is supplied it returns Promise<{ rows: M[]; count: { count: number }[]>>

The current type of Sequelize findAndCountAll is

  public static findAndCountAll<M extends Model>(
    this: ModelStatic<M>,
    options?: FindAndCountOptions<M['_attributes']>
  ): Promise<{ rows: M[]; count: number }>;

What do you expect to happen?

Since findAndCountAll returns two different results the type should ideally be

  public static findAndCountAll<M extends Model>(
    this: ModelStatic<M>,
    options?: FindAndCountOptions<M['_attributes']>
  ): Promise<{ rows: M[]; count: number | { count: number }[]>;

I have noticed other attributes also being returned inside the count object so just a count : { count: number } might not work.

What is actually happening?

As discussed in this issue to return the proper count I need to take a count of the returned count array. But since the type says count is a number I am unable to do so.

    const allUsersRaw = await this.User.findAndCountAll({
        attributes,
        include,
        where,
        order,
        limit,
        offset,
        group: ["Order.id"],
        subQuery: false
    });
    const count = allUsersRaw.count.length;

Following error is thrown

Property 'length' does not exist on type 'number'. ts(2339)

Environment

• Sequelize version: 6.6.2
• Node.js version: v16.3.0
• Operating System: MacOs BigSur 11.4
• If TypeScript related: TypeScript version: 4.3.2

Issue Template Checklist

How does this problem relate to dialects?

• I think this problem happens regardless of the dialect.
• I think this problem happens only for the following dialect(s):
• I don't know, I was using PUT-YOUR-DIALECT-HERE, with connector library version XXX and database version XXX

Would you be willing to resolve this issue by submitting a Pull Request?

• Yes, I have the time and I know how to start.
• Yes, I have the time but I don't know how to start, I would need guidance.
• No, I don't have the time, although I believe I could do it if I had the time...
• No, I don't have the time and I wouldn't even know how to start.