Good day, Richard.
DT> As result, __new type of system information__ appears:
As result, new type of system information appears -
field, refering to other field by foreign key, indeed contain two values:
(1) usual value, assinged into field by user
select FieldFK, ...
insert into ... values (FieldFK, ...)
(2) 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, ...)
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":
create/alter table ... (
...
FieldFK num3,
FieldFK#sys num2,
...
)
Also as result, it's possible to create stored procedures,
which, being started by not author, will executed in external database:
(1) under login of user, which start procedure
create procedure ...
(2) under login of author of procedure
create sticky procedure ...
Each database stores all nicknames, known for its users,
in system table 'pg_nicknames' for execution of stored procedures and timers
(some of nicknames can name database, in which this enumeration of nicknames
is).
IdUser al an username password IdDb nickname datatime
101 database.com Smith pwds 31 db1
101 123.123.123.123 33 db2
105 storage.com 234.234.234.234 Tomson 34 db1
'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. And:
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 'pg_nicknames'
(it is used for replication of tables 'pg_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
'pg_nicknames'
(next command 'default' will use table 'pg_nicknames' of new database, i.e. of
'db2'):
connect db2;
Command 'connect' affects to table 'pg_nicknames' of database, in which user
is: it
(1) updates field 'an' by value, got from DNS-server
(field 'an' itself exists for event of breakage of DNS-server)
(2) adds new records (in which field 'password'=null),
when user executes it into external database,
which yet not registered in 'pg_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
http://sql40.chat.ru/site/sql40/en/author/ddl_eng.htm#department )
connect
ra="data.storage.com" username="Johnson" password="pwdj" nickname="db4";
update pg_nicknames set password=pwdj where
ra="data.storage.com" username="Johnson" nickname="db4";
IdUser al an username password IdDb nickname datatime
101 data.storage.com 234.234.234.234 Johnson pwdj 38 db4
Summary of all ideas is in
http://sql40.chat.ru/site/sql40/en/author/mc_eng.htm
Dmitry Turin
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