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>most SQL will carry over between SQLite and Postgres and MySQL, especially if you add ORMs in the mix I think this goes underappreciated, or rather the opposi

>most SQL will carry over between SQLite and Postgres and MySQL, especially if you add ORMs in the mix I think this goes underappreciated, or rather the opposite is overstated. Sure there are some edge cases that don't work the same, but most apps won't hit those. My _biggest_ gripe with SQLite so far is the lack of column reordering like other DBs. And my simplistic understanding is that the others do it exactly the same way as you'd do it manually with SQLite - table gets _replaced_ with an identical table with the data correctly ordered and the data is shoved into the new table.

dkjaudyeqooe 3y ago
Why would you want to recorder columns? SQLite reads in a whole record at a time to access any column.
- anacrolix 3y ago
  Not true.
- masklinn 3y ago
  Because as in structs padding slack can lead to a surprising amount of overhead.
  - dkjaudyeqooe 3y ago
    That's not the case: "SQLite does not pad or align columns within a row. Everything is tightly packed together using minimal space." https://sqlite.org/forum/info/06ad7f81fea46401 https://sqlite.org/forum/info/06ad7f81fea46401
- simonw 3y ago
  I reorder columns all the time for neater readability of "select *" queries.
- prirun 3y ago
  One reason to reorder columns with SQLite is that if a column is usually null or has the default value, SQLite will not store the column at all if it is at the end of the row. It only saves a couple of bytes per column, but it is a reason to get these columns at the end.
  - masklinn 3y ago
    AFAIK position has nothing to do with nulls, a null is a 0 byte in the header and has no payload in the row: https://www.sqlite.org/fileformat.html#record_format https://www.sqlite.org/fileformat.html#record_format
    - prirun 3y ago
      Continue reading that section: "Missing values at the end of the record are filled in using the default value for the corresponding columns defined in the table schema." If you have a table with 5 columns and you only insert the first 3 columns (based on create table column order) because the last 2 values are null or default, SQLite will only insert 3 type bytes in the header. However, if the first column (in create table order) is the one you omit, SQLite has to include its type byte, even if the value is null.
masklinn 3y ago
> Sure there are some edge cases that don't work the same, but most apps won't hit those. That really depends on your modelling style. If you like things like types, SQL-side processing (eg using functions), or covering indexes, then you’ll hit issues every five minutes in sqlite. SQLite really wants the logic (including consistency logic) in the application, just compare the list of aggregate functions in postgres versus sqlite, or consider that you have to enable FKs on a per-connection basis. Which I guess is why ORMs help a lot: they are generally based on application-side logic and LCD database.
- simonw 3y ago
  I'm pretty sure SQLite has covering indexes. And the relatively new strict mode should enforce at least basic types (though if you want to enforce your own rules for things like dates you're still on your own).
  - masklinn 3y ago
    > I'm pretty sure SQLite has covering indexes. I checked to be sure I had not missed it, and didn’t find anything. You have expressions and conditions, but no covering. Obviously you can kinda emulate it by adding the columns you want to cover to the key, but… > though if you want to enforce your own rules for things like dates you're still on your own That’s what I was talking about, having richer types, and the ability to create more (especially domains). Strict tables provides table stakes of actually enforcing the all-of-5-types sqlite has built-in. Afaik a strict mode is something that’s still being discussed if it ever becomes reality.
    - simonw 3y ago
      "Obviously you can kinda emulate it by adding the columns you want to cover to the key" Right, that seems like a good solution to me.
      - masklinn 3y ago
        It’s a workaround, but it bloats the interior pages of the index with the covering data, which increases the size of the index and makes lookup less efficient (as they have to traverse more interior pages, and since there are more pages those are less likely to remain in cache).
cjblomqvist 3y ago
I think the bigger issue for many is that tooling, infra(provider), in-house knowledge/skill/experience as well as optimizations may differ quite a lot. Of course, this will differ a lot between projects.
simonw 3y ago
If you want a more convenient way to do column reordering (and other advanced alter table operations) in SQLite my sqlite-utils CLI tool can do this: sqlite-utils transform data.db mytable \ -o id -o title -o description That will change the order of the columns in the specified table such that id, title and description come first. The same command can handle many other operations such as changing column types, renaming columns or assigning a new primary key. https://sqlite-utils.datasette.io/en/stable/cli.html#transforming-tables https://sqlite-utils.datasette.io/en/stable/cli.html#transfo...
cztomsik 3y ago
column reordering is simple to fix with this migration script https://david.rothlis.net/declarative-schema-migration-for-sqlite/ https://david.rothlis.net/declarative-schema-migration-for-s... if you are using Zig (and like to live on the bleeding edge), you can also just use my library which includes similar script and also a simple query builder https://github.com/cztomsik/fridge?tab=readme-ov-file#migrations https://github.com/cztomsik/fridge?tab=readme-ov-file#migrat...

dkjaudyeqooe 3y ago

Why would you want to recorder columns? SQLite reads in a whole record at a time to access any column.

anacrolix 3y ago
Not true.
masklinn 3y ago
Because as in structs padding slack can lead to a surprising amount of overhead.
- dkjaudyeqooe 3y ago
  That's not the case: "SQLite does not pad or align columns within a row. Everything is tightly packed together using minimal space." https://sqlite.org/forum/info/06ad7f81fea46401 https://sqlite.org/forum/info/06ad7f81fea46401
simonw 3y ago
I reorder columns all the time for neater readability of "select *" queries.
prirun 3y ago
One reason to reorder columns with SQLite is that if a column is usually null or has the default value, SQLite will not store the column at all if it is at the end of the row. It only saves a couple of bytes per column, but it is a reason to get these columns at the end.
- masklinn 3y ago
  AFAIK position has nothing to do with nulls, a null is a 0 byte in the header and has no payload in the row: https://www.sqlite.org/fileformat.html#record_format https://www.sqlite.org/fileformat.html#record_format
  - prirun 3y ago
    Continue reading that section: "Missing values at the end of the record are filled in using the default value for the corresponding columns defined in the table schema." If you have a table with 5 columns and you only insert the first 3 columns (based on create table column order) because the last 2 values are null or default, SQLite will only insert 3 type bytes in the header. However, if the first column (in create table order) is the one you omit, SQLite has to include its type byte, even if the value is null.

masklinn 3y ago

> Sure there are some edge cases that don't work the same, but most apps won't hit those. That really depends on your modelling style. If you like things like types, SQL-side processing (eg using functions), or covering indexes, then you’ll hit issues every five minutes in sqlite. SQLite really wants the logic (including consistency logic) in the application, just compare the list of aggregate functions in postgres versus sqlite, or consider that you have to enable FKs on a per-connection basis. Which I guess is why ORMs help a lot: they are generally based on application-side logic and LCD database.

simonw 3y ago
I'm pretty sure SQLite has covering indexes. And the relatively new strict mode should enforce at least basic types (though if you want to enforce your own rules for things like dates you're still on your own).
- masklinn 3y ago
  > I'm pretty sure SQLite has covering indexes. I checked to be sure I had not missed it, and didn’t find anything. You have expressions and conditions, but no covering. Obviously you can kinda emulate it by adding the columns you want to cover to the key, but… > though if you want to enforce your own rules for things like dates you're still on your own That’s what I was talking about, having richer types, and the ability to create more (especially domains). Strict tables provides table stakes of actually enforcing the all-of-5-types sqlite has built-in. Afaik a strict mode is something that’s still being discussed if it ever becomes reality.
  - simonw 3y ago
    "Obviously you can kinda emulate it by adding the columns you want to cover to the key" Right, that seems like a good solution to me.
    - masklinn 3y ago
      It’s a workaround, but it bloats the interior pages of the index with the covering data, which increases the size of the index and makes lookup less efficient (as they have to traverse more interior pages, and since there are more pages those are less likely to remain in cache).

cjblomqvist 3y ago

I think the bigger issue for many is that tooling, infra(provider), in-house knowledge/skill/experience as well as optimizations may differ quite a lot. Of course, this will differ a lot between projects.

simonw 3y ago

If you want a more convenient way to do column reordering (and other advanced alter table operations) in SQLite my sqlite-utils CLI tool can do this: sqlite-utils transform data.db mytable \ -o id -o title -o description That will change the order of the columns in the specified table such that id, title and description come first. The same command can handle many other operations such as changing column types, renaming columns or assigning a new primary key. https://sqlite-utils.datasette.io/en/stable/cli.html#transforming-tables https://sqlite-utils.datasette.io/en/stable/cli.html#transfo...

cztomsik 3y ago

column reordering is simple to fix with this migration script https://david.rothlis.net/declarative-schema-migration-for-sqlite/ https://david.rothlis.net/declarative-schema-migration-for-s... if you are using Zig (and like to live on the bleeding edge), you can also just use my library which includes similar script and also a simple query builder https://github.com/cztomsik/fridge?tab=readme-ov-file#migrations https://github.com/cztomsik/fridge?tab=readme-ov-file#migrat...