Is there any chances that it will work on replicas?
...
sure, it should to work. Now, I am try to solve a issues on concept level - the LET code is based on DML code base, so probably there is check for rw transactions. But it is useless for LET command.
Very, very good! As I understand, the work on this patch now in progress and it not in commitfest. Please explain what features of schema variables I can review now.
From first post of this thread the syntax of the CREATE VARIABLE command: CREATE [TEMP] VARIABLE [IF NOT EXISTS] name AS type [ DEFAULT expression ] [[NOT] NULL]
[ ON TRANSACTION END { RESET | DROP } ]
[ { VOLATILE | STABLE } ];
Now, it is too early for review - it is in development. Some features are not implemented yet - DEFAULTs, ON TRANSACTION END .., others has not sense (what I know now VOLATILE, STABLE). Schema variables are passed as parameters to query, so the behave is like any other params - it is STABLE only.
But in psql I see only: \h create variable Command: CREATE VARIABLE Description: define a new permissioned typed schema variable Syntax: CREATE VARIABLE [ IF NOT EXISTS ] name [ AS ] data_type ]
I can include DEFAULT clause in CREATE VARIABLE command, but the value not used:
postgres=# create variable i int default 0; CREATE VARIABLE postgres=# select i; i ---
(1 row)
postgres=# \d+ i schema variable "public.i" Column | Type | Storage --------+---------+--------- i | integer | plain
defaults are not implemented yet
BTW, I found an error in handling of table aliases:
postgres=# create variable x text; CREATE VARIABLE postgres=# select * from pg_class AS x where x.relname = 'x'; ERROR: type text is not composite
It thinks that x.relname is an attribute of x variable instead of an alias for pg_class table.
It is not well handled collision. This should be detected and prohibited. In this case, because x is scalar, then x.xx has not sense, and then it should not be handled like variable. So the current design is not too practical - it generates more collisions than it is necessary and still, there are some errors.
Now, there is one important question - storage - Postgres stores all objects to files - only memory storage is not designed yet. This is part, where I need a help.