Hi, ALL,

If I work with one DB than in my C++ code I can run

SELECT * FROM pragma_table_info(?)

and everything works fine.

However if I have a second DB ATTACH'ed running

SELECT * FROM <schema>.pragma_table_info(?)

will fail because neither of those DBs have a tale that called "pragma_table_info"

So how do I execute such query against ATTACH'ed DB?

Thank you.

The pragma function belongs to the connection, not the DB schema.

In other words,

in stead of:
SELECT * FROM <schema>.pragma_table_info(<table>);

rather try:
SELECT * FROM pragma_table_info(<schema>.<table>);

That is incorrect.

To select from the eponymous pragma tables that take an object name and a schema as argument you must present the arg first and the schema second, or use the appropriate WHERE clause names, and the object names must be text strings, not object referents.

select * from pragma_table_info('<table>', '<schema>')

or

select * from pragma_table_info where schema='<schema>' and arg='<table>'

This applies to all virtual tables, whether eponymous or not. The "input" parameters may appear either as arguments to the virtual table name itself or in the where clause.

select value from generate_series where start=1 and stop=10

or equivalently

select value from generate_series(1,10)

However if I have a second DB ATTACH'ed running

SELECT * FROM <schema>.pragma_table_info(?)

will fail because neither of those DBs have a tale that called pragma_table_info"

This is an incorrect statement *you obviously did not try it).

"real" objects, which includes virtual tables, exist within the confines of a specific schema -- the one in which the CREATE <whatever> was executed. Specifying a different schema from the one in which the object was created (and in which the object does not exist) will return a object does not exist error.

eponymous virtual tables (such as the pragma tables, generate_series, wholenumber, and so on and so forth) are owned by the connection itself and do not "exist" within the confines of any specific schema (they were not created by executing a CREATE <object> statement) but rather are a creature of the connection. As such any resolvable schema name that exists within the connection may be used when referencing such objects, and all such referents refer to the very self-same eponymous virtual table indifferently to the schema reference used or not used.

any resolvable schema name that exists within the connection may be used when referencing such objects

Not quite any...

sqlite> create temp table pragma_table_info (id integer primary key);
sqlite> select * from pragma_table_info('pragma_table_info');
Parse error: 'pragma_table_info' is not a function
sqlite> select * from main.pragma_table_info('pragma_table_info');
+-----+------+---------+---------+------------+----+
| cid | name |  type   | notnull | dflt_value | pk |
+-----+------+---------+---------+------------+----+
| 0   | id   | INTEGER | 0       |            | 1  |
+-----+------+---------+---------+------------+----+
sqlite> select * from main.pragma_table_info('pragma_table_info','main');
+-----+------------+------+---------+------------+----+
| cid |    name    | type | notnull | dflt_value | pk |
+-----+------------+------+---------+------------+----+
| 0   | cid        |      | 0       |            | 0  |
| 1   | name       |      | 0       |            | 0  |
| 2   | type       |      | 0       |            | 0  |
| 3   | notnull    |      | 0       |            | 0  |
| 4   | dflt_value |      | 0       |            | 0  |
| 5   | pk         |      | 0       |            | 0  |
+-----+------------+------+---------+------------+----+

You are confounding yourself by creating an object with the same name as an eponymous virtual table which will, of course, change the search rules.

When you are not in control of the schema, assume malice and code defensively.