World: r3wp

I tried to use: CREATE TABLE IF NOT EXISTS but I get an error if 
I use this line and the table already exists.

The SQLite docs say:

 If the optional IF NOT EXISTS clause is present and another table 
 with the same name aleady exists, then this command becomes a no-op.

Did anybody tested to open sqlite.r generated databases with a database 
manger? I can't. In one tool I can see the database but not tables, 
even I have created one.

And if I use the TABLES command I get:
>> print tables

material CREATE TABLE material (_id INTEGER PRIMARY KEY AUTOINCREMENT,_version,_benchmark,_prev,_next,_product_id,name,price,pcdl,pudl,netto,nudl,scrap,loss,process_loss,scrap_re

cycle_rate,scrap_recycle,srcdl,srudl,process_loss_recycle_rate,process_loss_recycle,plrcdl,plurdl) 
sqlite_sequence CREATE TABLE sqlite_sequence(name,seq)

The docs state that I get beck the number of columns and rows... 
Any idea?

Using sqlite.r I can acess the table and get back my values.

And I can't get back the columns name. sqlite/columns returns an 
empty block.

anybody tested to open sqlite.r generated databases with a database 
manger?
 Not sure what you mean here. The following works fine for me:

	c:\> sqlite3.exe my-db.db

docs state that I get back the number of columns and rows
 ... no longer the case (docs need to be updated)


Most efficient way to get number of rows is sql "select count(*) 
from my-table"


Number of columns can be found by: (length? describe "my-table") 
/ 6

I can't get back the columns name

 ... use the DESCRIBE command, or CONNECT/info (which then populates 
 sqlite/columns and sqlite/widths for every query; or alternatly, 
 set sqlite/col-info? true / false for a particular query).

A simple rows function:

	set 'rows make function! [
		"Return row count."
		table [string!]
	][
		first sql/flat/direct reform ["select count(*) from" table]
	]

just add it to the body of the sqlite context.

Thanks.

WRT encryption. I found one implementation (you need to buy a license) 
that supports transparent encryption. IIRC I posted the link some 
time ago. I will have a look at the C code and there at the storage 
stuff to see how hard it is to add an AES encryption of storage pages. 
IMO it can't be that hard.

0.2.0 available at: http://www.dobeash.com/SQLite/


Incorporates minor fixes / changes discussed since 0.1.9, with documentation 
updated to match (some content was also moved from the old Driver 
Guide to the new User Guide).

I was just reading the User Guide on that site and I noticed that 
there were some parts of the docs on the DESCRIBE function that you 
seemed to have some questions about, particularly the meaning of 
some of the returned columns. (Sorry if I am in error about that.)


- On the table column listing, the notnull column refers to whether 
you are allowed to insert a NULL in that column. The pk column tells 
you whether the column is a primary key. Primary keys in SQLite are 
always integer and are their way of doing autonumber fields.


- On the indexes listing, a unique index also makes sure that the 
combination of values that the index applies to won't be duplicated 
in the table.

Thanks, I've updated the page (replacing my shorthand for a flag, 
?, with the word flag). If anyone has a description of the columns 
for FKeys just holler and I'll add it in.

I'm not sure it matters yet. SQLite doesn't check foreign key constraints 
yet, so any such constraints are just documentation right now.

Still, here they are (best estimate based on reading the SQLite C 
source):

- id: The index of the foreign key in the list of foreign keys for 
the table, 0-based (integer)

- seq: The index of the column referenced in the foreign key, 0-based 
(integer)
- table: The name of the referenced table (string)
- from: The column name in the local table (string)
- to: The column name in the referenced table (string)

id: Isn't ID only unique for every table? Yours read like ID is unique 
for the complete database.

No, this is a diagnostic table generated by a pragma statement. It 
isn't really a table internally. Still, the key for this "table" 
is (id,seq) and it is generated by a pragma that takes the table 
name as a parameter, so it is a seperate "table" for each real table.

It really is a linked list internally - that's why I called it that 
:)

Each "row" of the "table" refers to a column referenced by a foreign 
key that may refer to more than one column.

And a table may have more than one foreign key.

And all of these foreign keys are currently meaningless because they 
aren't currently checked by SQLite - they are just documentation.

Still, you could make a tool that actually read these foreign keys 
and checked them externally if you want...

IIRC you can even access those internal tables of SQLite and query 
them.

Well, for the most part this database metadata isn't really stored 
in tables in SQLite. Instead queries about the metadata are generated 
from internal structures when needed, by pragma statements. Still, 
the effect is the same.

It's kind of cool really when you read how this is done. I guess 
things can be a lot more interesting for a single-user embedded database 
engine. You can see where SQLite gets its high performance.

I have to take a look at the C code. But #pragma stuff is compile 
time...

No, not C pragma, a set of PRAGMA statements that SQLite extensions 
to SQL, for settings and diagnostics.

...that _are_ SQLite extensions...

Check http://www.sqlite.org/pragma.html

The statement that returns the result set we were talking about is:
    PRAGMA foreign_key_list(table-name);

Thanks, updated page.

Ah, ok. Now I get it.

 wtcSQLite allows you to add/edit/delete indexes, fields, tables, 
 triggers, views, data, and manage multiple database aliases without 
 knowing any SQL at all. 
http://www.zend.com/php5/contest/contest.php?id=74&single=1

(it's phpmyadmin for sqlite)

Q: If I have a table with let's say 1 million records and I do a 
query that returns 250.000 records as result set. Do I get all of 
them copied into Rebol? Or can I access this result set "pagewise"?

What's the best pattern to handle such hughe tables?

The best pattern for such huge tables?
MySQL

No, no option for me.

So, what can be done is SELECT ... LIMIT n OFFSET m. At least this 
can handle the result set in defined block sizes on the application 
level. Of course paging requires a new query each time.

It all depends.


 250,000 integers vs 250,000 multi-column rows with large string values
	client device with 16MB RAM vs 'server' with 4GB RAM
	'local' query vs pulling the data over a network


There are plenty of optimization strategies. One technique, if concurrency 
is not an issue for you, is to have your query return 250,000 rowids 
then page through rows based on simple 'rowid in (...)' type queries. 
It's fast and efficient, but not too great if others are modifying 
the same table(s) at the same time.

I have no concurrency issue. Yes, this might be a good solution too.

Could you use a cursor?

(That would work with many other SQLs....Not sure about MySQL's support 
for them)

Yes, but SQLite doesn't has this concept. So you can only move forward 
through a result set. But the set isn't known at this stage.

That's a pity.

What's the best way to get back the columns of a table ONCE? I just 
need the column names in left-to-right order inside the table.

How do you solve the problem of schema changes? You develop an app 
and over time you see that some columns need to be added/removed 
from tables? What's the best strategy to do this?

output to csv, import?

This mean on every update the user has to do this cycle... don't 
think this is an option.

Adding is easy - I think SQLite supports ALTER TABLE ADD COLUMN.

well, how often do you adjust your tables? ;-) then it is not good 
design imo ...