[josephg]

Eh. What people are really arguing about here is redis’s type system. Redis’s approach has some pros and some cons. I think dismissing redis’s approach out of hand for its choices is too simple a treatment.

Most sql databases (like Postgres) require all types to be declared once, and then they do type checking on mutation. In that sense, sql is like a static language like C. But weirdly, the results returned from a sql query are always dynamically typed values, expressed in a table. Applications reading data from sql will still typically need to know what kind of data they expect back - but they usually do that type checking at runtime.

Redis flips both of those choices. It’s dynamically typed - so it won’t check your mutations. But also, you don’t need schema migrations and all the complexity they bring. And rather than having a single “table” type, redis queries can return scalar values, lists or maps. What kind of return value you get back depends on the query function. (Eg GET vs LRANGE).

If you think of a database as the foundation underneath your house, static typing & type checking is a wonderful way to make that foundation more stable. There’s a reason Postgres is the default, after all. But redis isn’t best used like that. Instead, it’s a Swiss Army knife which is best used in small, specific situations in which a real database would be complex overkill. Stuff like caching, event processing, data processing, task queues, configuration, and on and on. Places where you want some of the advantages of a database (fast, concurrent network-accessible storage) but you don’t want to stress about tables and schema migrations.

If you really hate redis, maybe say the same thing I say about Java when I teach it to my students. “I hate this, and I’ll tell you why. But there are smart people out there who disagree with me.”

If you ask me, I wish sql looked more like redis in some ways. I think it’s quite awkward that every sql query returns exactly one “table”. I’d much rather if queries could return scalar values or even multiple tables, depending on your query.

[gregw2]

Minor nit. Some SQL databases allow you to return multiple tables. IIRC, SQL Server stored procedures can do that. Agreed its not a language feature of SQL.

[CRConrad]

> I’d much rather if queries could return scalar values

Since when can't they?

[josephg]

I mean, they can - but they’re always wrapped up as pseudo-tables.

Not everything is best described as a table, y’know?

[CRConrad]

> they’re always wrapped up as pseudo-tables.

Are they??? Not as I understand it.

[josephg]

If you call “select 1;”, you get back a table with 1 row and 1 column.

[CRConrad]

That's just because SQL clients present their results that way, AFAICS. If you use a sub-query like in, say,

   select * from orders where custno = (select custno from customers where name = 'John Doe');

you'll get the same result as if you'd put that scalar in your query, like

   select * from orders where custno = 123456; -- John Doe's customer number

Or maybe you're right, that to SQL databases scalar values are single-row single-column tables. But so what? In mathematics, isn't any number also the single-member set of numbers that contains only that number? Where's the harm in that? (And, hey, RDBMSes are founded on set theory...)

So I don't really see what the big problem is either way. Hoping I'm not being stupid AF, maybe you could explain further?

[josephg]

Mathematically, they're equivalently expressive. But returning everything as a table has bad ergonomics.

Imagine the programming language equivalent. We could make a programming language where every function call returns a table. If you expect 1 return value from your function, the caller grabs the first row out of the return array, and the first column out of that row. It would absolutely work, and that its mathematically equivalent in some sense. But it would be confusing, computationally inefficient and error prone. What happens if there's more than 1 row in the table? Or more than 1 column? What happens if the type of the columns doesn't match match what you expect? What happens if the table is empty? Or you want a function which returns a two lists instead of one? We could write that programming language. But it would be pretty weird and frustrating to use.

This is the situation today with SQL. Every query returns a dynamically typed table. Its up to the caller to parse that table.

With redis, the caller expresses to the database what kind of value they expect in the query function name. (At least, list or scalar). The database guarantees that a GET request always returns a scalar value, and LRANGE always returns a list. I think this has better ergonomics because the types are more explicit.