[mytherin]

Most implementations of SQL are not dynamically typed - they are statically typed. There is an explicit compilation phase (`PREPARE`) that compiles the entire plan and handles any type errors.

For example - this query throws a type error when run in Postgres during query compilation without executing anything or reading a row of the input data:

   CREATE TABLE varchars(v VARCHAR);
   PREPARE v1 AS SELECT v + 42 FROM varchars;

   ERROR:  operator does not exist: character varying + integer
   LINE 1: PREPARE v1 AS SELECT v + 42 FROM varchars;
                               ^
   HINT:  No operator matches the given name and argument types. You might need to add explicit type casts.

The one notable exception to this is SQLite which has per-value typing, rather than per-column typing. As such SQLite is dynamically typed.

[randomdata]

That is strong typing. Python, a dynamically typed language, exhibits the same quality:

    >>> v = ""
    >>> v + 42
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: can only concatenate str (not "int") to str

Types are most certainly not static (at least not in Postgres or most other implementations):

    CREATE TABLE varchars(v VARCHAR);
    ALTER TABLE varchars ALTER COLUMN v TYPE INTEGER USING v::integer;
    PREPARE v1 AS SELECT v + 42 FROM varchars;

[mytherin]

Types are static within the context of a query, not necessarily within the context of the lifetime of a database. Types are determined and propagated at query compile time. In a query, the value "v" refers to a VARCHAR column (as determined by the table definitions). At query compile time an error is thrown when a type violation is detected.

It is distinct from Python because in Python individual objects have types - and type resolution is done strictly at run-time. There is no compile time type checking because types do not exist at compile time at all. Note how in my example I am preparing (i.e. compiling) a query, whereas in your example you are executing the statement.

If you refrain from changing the types of columns in a database and prepare your queries you can detect all type errors before having to process a single row. That is not possible in a dynamically typed language like Python, and is very comparable to the guarantees that a language like Typescript offers you.

[randomdata]

> Types are static within the context of a query

Types in Python are also static within the context of a statement. That's not particularly meaningful, though, as programs don't run as individual statements in a vacuum. Just like SQL, the state that has been built up beforehand is quite significant to what each individual statement ends up meaning.

> types do not exist at compile time at all.

Same goes for SQL. Given the previous program, it is impossible to determine what the type of v is until you are ready to execute the SELECT statement. If the CREATE TABLE statement fails, v will not be the VARCHAR you think it is. If someone else modifies the world between your CREATE TABLE statement and your SELECT statement, v also will not be the VARCHAR you think it is. All you can do is throw the code at the database at runtime and hope it doesn't blow up.

> whereas in your example you are executing the statement.

What do you think "" + 42 executes to, then? The thing is, it doesn't execute because it doesn't satisfy the type constraints. It fails before execution. If it were a weakly typed language, like Javascript, then execution may be possible. Javascript produces "42".

> and is very comparable to the guarantees that a language like Typescript offers you.

Not at all. Something like Typescript provides guarantees during development. SQL, being a dynamically typed language, cannot know the types ahead of time – they don't exist until the program has already begun execution – and will throw errors at you in runtime after you've moved into production if you've encountered a problem.

[mytherin]

> Same goes for SQL. Given the previous program, it is impossible to determine what the type of v is until you are ready to execute the SELECT statement. If the CREATE TABLE statement fails, v will not be the VARCHAR you think it is. If someone else modifies the world between your CREATE TABLE statement and your SELECT statement, v also will not be the VARCHAR you think it is. All you can do is throw the code at the database at runtime and hope it doesn't blow up.

If you are working in a hypothetical adversarial world where people are changing data types out from under you then that might happen. That will also happen with any other shared data source, regardless of what language you might be using. If you are sharing a set of JSON documents and people start altering documents and removing keys then your Typescript program that ingests those documents will also start failing.

That is not a problem of the language but a fundamental problem of having a shared data source - changing to a different language will not solve that problem.

I think you are conflating SQL the language with a relational database management system. A relational database management system models a shared data source - and a shared data source can be modified by others. That introduces challenges no matter what language you are using.

> What do you think "" + 42 executes to, then? The thing is, it doesn't execute because it doesn't satisfy the type constraints. It fails before execution. If it were a weakly typed language, like Javascript, then execution may be possible. Javascript produces "42".

It is fundamentally different. Given a Python program, you cannot know whether or not it will produce type errors at run-time without executing the program. Type checking is done at run-time as part of the execution of the "+" operator. In SQL, type checking is done as a separate compilation step that can be performed without requiring any data. In Python the object has a type. In SQL the variable has a type.

Given a fixed database schema and a set of queries, you can compile the queries and know whether or not the queries will provide type errors. You cannot do this with Python.

> Not at all. The benefits of something like Typescript is that the guarantees are provided during development. SQL cannot know the types ahead of time – they don't exist until the program has begun execution – and will throw errors at you in runtime after you've moved into production if you've encountered a problem. That's exactly when you don't want to be running into type programs, and why we're largely moving away from dynamically typed languages in general.

SQL can provide the same guarantees as Typescript. However, unlike Typescript in which the variables are fixed, SQL always deals with processing data from an external data source - the tables. The data sources (i.e. tables) can be changed. That is not a problem a language can solve.

[randomdata]

> Given a Python program, you cannot know whether or not it will produce type errors at run-time without executing the program.

Like you mentioned earlier, if you refrain from changing types, a compiler can theoretically determine Python types as well. The Typescript type checker when run on Javascript code is able to do this. But that puts all the onus on you to be super careful instead of letting the language hold your hand.

> SQL can provide the same guarantees as Typescript.

1. It cannot as it does not provide guarantees about its memory model. Declaring a variable as a given type does not guarantee the variable will be created with that type. Typescript does guarantee that when you declare a type that's what the variable type is going to be.

2. As SQL is dynamically typed, allowing you to change the type of a variable mid-execution, what type a variable is depends on when that statement is up for execution. And as SQL is not processed sequentially, at least not in a meaningful sense, it is impossible for a compiler to determine when in the sequence it will end up being called upon.

[mytherin]

Again, you are still conflating tables in a relational database with variables in Typescript. While I can understand the confusion - given that SQL makes it so natural to interact with tables - they are not equivalent.

SQL as a language is statically typed. It has variables that are statically typed [1], much like Typescript. All columns in a query have fixed types, and there is a separate compilation phase that resolves types of parameters - much like any other statically typed language.

SQL generally operates on tables - and tables model a persistent, shared data source. The Typescript equivalent to a table is JSON files on disk. There is a fundamental need to be able to change data sources as time goes on and business requirements change. That is why SQL supports modifying shared data sources, and supports operations like adding columns, changing column types and dropping columns. SQL deals with the fact that changes can be made to tables by rebinding (recompiling) queries when a data source is changed.

Any hypothetical language that will replace SQL will have to deal with the very same realities of people wanting to modify shared data sources. A different language cannot solve this problem because there is a fundamental need to change how data is stored at times.

Perhaps what you are looking for is better tooling around this problem. SQL can be used to power such tooling, because of its strong static type system that works alongside the persistent shared data source. For example - you could check if all your queries will still successfully compile after changing the type of a column.

[1] https://www.postgresql.org/docs/current/plpgsql-declarations...