PostgreSQL: Return filtered rows along with total number of rows matching a condition - postgresql

Question

Say I have a table, posts, that I'm able to query and filter on a client app. Each post has a type associated with it, and I'd like to be able to see both the filtered posts on the client and the total number of rows that match the filters by type on a dashboard. Obviously, I'd like to do this in a single query. It's also important to note that I'm paginating the data so I can't just use filter(...).length in some backend logic, as there might be 100000 posts but only 10 returned to the client.
Here's my query that correctly filters the data:
knex('posts').select('id', 'created_at', 'content', 'type').modify((builder) => (
filterPosts(builder, filters)
)).paginate({currentPage: offset, perPage: limit})
I'm wondering if there's some way to count the number of posts (by type) that match the filters, and return those counts in my existing query.
E.g. my results currently look like this:
[
{
id: 123,
created_at: "Jan 1, 2022",
content: "Lorem ipsum",
type: "Type 1"
},
{
id: 456,
created_at: "Feb 1, 2022",
content: "Ipsum dolor",
type: "Type 2"
}
...
]
and I'd like something like this:
[
{
id: 123,
created_at: "Jan 1, 2022",
content: "Lorem ipsum",
type: "Type 1"
countType1: 3, // Total rows where type = "Type 1" that match the filters
countType2: 6 // Total rows where type = "Type 2" that match the filters
},
{
id: 456,
created_at: "Feb 1, 2022",
content: "Ipsum dolor",
type: "Type 2",
countType1: 3,
countType2: 6
}
...
]
I've tried using a window function but so far can only get the number of posts of the current row's type, not all types
knex('posts').select(
'id',
'created_at',
'content',
'type',
'count(*) over (partition by posts.type)' // If I could add a WHERE clause here I'd be golden
).modify((builder) => (
filterPosts(builder, filters)
)).paginate({currentPage: offset, perPage: limit})
The above gives:
[
{
id: 123,
created_at: "Jan 1, 2022",
content: "Lorem ipsum",
type: "Type 1"
count: 3,
},
{
id: 456,
created_at: "Feb 1, 2022",
content: "Ipsum dolor",
type: "Type 2",
count: 6
}
...
]
Which isn't optimal since it's possible that 10 posts of only Type 2 are returned to the client due to the pagination, making the client think there are 0 posts of Type 1.
Open to suggestions on how to improve this, any help is greatly appreciated!
This post seems to be on the right track but I can't figure out how to get it working for my scenario

Answer 1

I was able to solve this by building off that post I linked:
knex
.with(
'posts',
knex
.from(
knex('posts').select(
{ id: 'posts.id' },
{ created_at: 'posts.created_at' },
{ content: 'posts.content' },
{ type: 'posts.type' },
)
)
.modify((builder) => filterPosts(builder, filters)) // Contains joins and where clauses
)
.from('posts')
.rightJoin(
knex.raw(
"(select count(1) filter(where posts.type = 'Type 1'), count(1) filter(where posts.type = 'Type 2') from posts) c(type_1_count, type_2_count) on true"
)
)
.select(
'posts.*',
'type_1_count',
'type_2_count'
);