Abilio Marques wrote on Sunday, August 23, 2015 4:42 PM
>
> 3. Lua can return arrays. Also, Lua can return multiple values. Tried
> to take advantage of those facts, but while reading the SQLite API
> documentation, found no function where I could map multiple values as
> the return of a function. Am I wrong? For example:
>
> select * from table t where fieldA in (lua('return 1,2,3'));
>
> Could be a useful feat in real scripts with real code.
Something that I've done that's similar-but-different is to use a C
preprocessor to preprocess the query, evaluating the Lua prior to the query
being prepared in sqlite.
In that case (slightly adapted from your example, assuming a lua function named
'csv')
select * from table t where fieldA in (lua('return csv(1,2,3)'));
resolves to
select * from table t where fieldA in (1,2,3);
that's still a single return value, but the ability to programmatically
manipulate the query prior to execution has been useful to me, particularly
being able to write things like
select * from lua('most_recent_table()') t where fieldA in (1,2,3);
or
attach database lua('get_right_dbfile()') as "db1";
assuming that LuaSqlite3 is available, the Lua functions can inspect the
database in order to implement their logic. LuaFileSystem can be useful as
well.
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