I may be misunderstanding something basic here, but I'm struggling to find this issue being explained in my research.

Let's say we have a users table and other tables that relate to the user, let's call them:

• orders (contains a userId)
• reviews (contains a userId)
• vaccinations (contains a userId)

Each user can have many orders, or reviews, or vaccinations.

Now let's say for whatever code I'm writing I want to get all users, all their orders, reviews and vaccinations.

Should I be writing one query that left joins everything together, or three separate queries?

I.E should it be something like:

SELECT * FROM users LEFT JOIN orders ON orders.userId = users.id LEFT JOIN reviews ON reviews.userId = users.id LEFT JOIN vaccinations ON vaccinations.userId = users.id

Or three completely separate queries like:

1. SELECT * FROM users LEFT JOIN orders ON orders.userId = users.id

2. SELECT * FROM users LEFT JOIN reviews ON reviews.userId = users.id

3. SELECT * FROM users LEFT JOIN vaccinations ON vaccinations.userId = users.id

Some background

I think what's causing me confusion is that most my time spent querying SQL is using the node ORM Sequelize. It allows me to happily query the database using a single query that on the face of it makes sense. Something like this:

return models.users.findAll({
include: [{
    model: models.orders
    required: false
},
{ 
    model: models.reviews,
    required: false
}, 
{
    model: models.vaccinations, 
    required: false
}],

});

In code it returns the results to me in a really nice ordered way that makes a lot of sense. However, what I realised when looking at the MySQL 'slow query' log is that some of these joins were returning hundreds of thousands of results per query. I guess this is due to how one extra row in one of the tables means the query then returns many more results.

Just to repeat the question to end with Should I be writing one query that left joins everything together, or three separate queries?

Thank you so much for your help.

I may be misunderstanding something basic here, but I'm struggling to find this issue being explained in my research.

Let's say we have a users table and other tables that relate to the user, let's call them:

• orders (contains a userId)
• reviews (contains a userId)
• vaccinations (contains a userId)

Each user can have many orders, or reviews, or vaccinations.

Now let's say for whatever code I'm writing I want to get all users, all their orders, reviews and vaccinations.

Should I be writing one query that left joins everything together, or three separate queries?

I.E should it be something like:

SELECT  *
    FROM  users
    LEFT JOIN  orders  ON orders.userId = users.id
    LEFT JOIN  reviews  ON reviews.userId = users.id
    LEFT JOIN  vaccinations  ON vaccinations.userId = users.id 

Or three completely separate queries like:

1. SELECT * FROM users LEFT JOIN orders ON orders.userId = users.id

2. SELECT * FROM users LEFT JOIN reviews ON reviews.userId = users.id

3. SELECT * FROM users LEFT JOIN vaccinations ON vaccinations.userId = users.id

Some background

I think what's causing me confusion is that most my time spent querying SQL is using the node ORM Sequelize. It allows me to happily query the database using a single query that on the face of it makes sense. Something like this:

return models.users.findAll({
include: [{
    model: models.orders
    required: false
},
{ 
    model: models.reviews,
    required: false
}, 
{
    model: models.vaccinations, 
    required: false
}],

});

In code it returns the results to me in a really nice ordered way that makes a lot of sense. However, what I realised when looking at the MySQL 'slow query' log is that some of these joins were returning hundreds of thousands of results per query. I guess this is due to how one extra row in one of the tables means the query then returns many more results.

Just to repeat the question to end with Should I be writing one query that left joins everything together, or three separate queries?

Thank you so much for your help.