Referencing into several databases in one request
One request can address to several databases simultaneously,
if location of object is specified by prefix,
which is before name of object through colon.
Prefix can be
As result, new type of system information appears -
field, refering to other field by foreign key,
indeed contain two values:
And as result we can give possibility to refer to external database by foreign key
at creating or altering table,
or not give (deprive this possibility) -
it is doing by creating (adding) or not creating (deleting) of field,
name of which is finished by "#sys":
- usual value, assinged into field by user
select FieldFK, ...
insert into ... values (FieldFK, ...)
- system value, which contain identifier of external database
(if record, to which field refers, is in external database)
and to which it's possible to refer, if to write "#sys" after name of field,
containing usual value:
select FieldFK#sys, ...
insert into ... values (FieldFK#sys, ...)
Also as result, it's possible to create stored procedures,
which, being started by not author,
will executed in external database:
create/alter table ... (
- under login of user, which start procedure
- under login of author of procedure
create sticky procedure ...
System table of nicknames
Each database stores all nicknames, known for its users,
in system table 'sys-nicknames'
for execution of stored procedures and timers
(some of nicknames can name database,
in which this enumeration of nicknames is).
- 'IdUser' is unique identifier of user in this database
- 'al' (address literal) is DNS-address
- 'an' (address numeric) is IP-address
- if 'al'≠null, then it is used
- if field 'al'=null, then 'an' is used
- 'username' is name of user in external database
- 'password' is password of user in external database.
- SQL-command or stored procedure, refering to external database,
asks username for external database in program-terminal
(if 'username'=null for this 'IdUser' and for this nickname)
and password (if 'password'=null)
- timer, refering to external database,
will not begin execution, if 'username'=null or 'password'=null,
nothing question will be
- 'IdDb' is identifier of external database,
unique inside this database
(if 'IdDb'=null, then it is database, in which this record itself is)
- 'nickname' is nickname of external database
(several different 'IdUser' can have identical 'nickname'
with identical or different 'al' and 'an',
but one 'IdUser' cann't has two identical 'nickname')
- 'datatime' is data of last updating of this record of table 'sys-nicknames'
(it is used for replication of tables 'sys-nicknames')
It's possible to change database, in which user "is",
by command 'connect',
in which username, password and address of database are not specified -
username, password and address of database will be taken from table 'sys-nicknames'
(next command 'default' will use table 'sys-nicknames' of new database,
i.e. of 'db2'):
Command 'connect' affects to table 'sys-nicknames' of database,
in which user is: it
- updates field 'an' by value, got from DNS-server
(field 'an' itself exists for event of breakage of DNS-server)
- adds new records (in which field 'password'=null),
when user executes it into external database,
which yet not registered in 'sys-nicknames' with new 'ra' and 'username'
(value of field 'password' is set by command 'update',
rights of access are given to user
on each record separately,
including to each record of system table)
ra="data.storage.com" username="Johnson" password="pwdj" nickname="db4";
update sys-nicknames set password=pwdj where
ra="data.storage.com" username="Johnson" nickname="db4";
After all said, replication of databases by branded programs
loss all sense -
always it's possible to make it by extension of SQL,