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Session functions

A session function reports the session of a statement. It reports nothing about a row. It takes no argument.

The functions​

FunctionReturnsDescription
current_database()STRINGThe database of the statement. It is NULL for a statement at the level of the server, such as CREATE DATABASE or CREATE USER. Such a statement has no current database.
current_user()STRINGThe name of the authenticated user. It is NULL while authentication is disabled.
current_role()STRINGThe same value as current_user().
is_superuser()BOOLWhether the session of the caller is a superuser. It is NULL while authentication is disabled.
SELECT current_user(), current_database(), is_superuser();

A session function works at any position that accepts a scalar function. That includes a SELECT without a FROM, a projection, a filter, and a key of a GROUP BY:

SELECT id, total
FROM orders
WHERE owner = current_user();

A NULL means that there is no identity​

While authentication is disabled, there is no authenticated identity to report. current_user() therefore returns NULL. It does not return a name as a placeholder. A name would assert an identity that the server never verified. See Authentication And Authorization.

current_role() and current_user() are the same​

CamusDB grants a privilege to a user directly. A session therefore has no identity of a role, separate from its user. current_role() exists so that SQL still runs. That SQL comes from an engine that separates the two ideas.

A session function bypasses the result cache​

The value of a session function is fixed for one session. It differs between two sessions. The query result cache belongs to one node, and every caller shares it.

A cache of SELECT current_user() would serve the identity of one caller to the next caller. Any query with a session function therefore bypasses the cache completely.

Not in a DEFAULT, and not in a CHECK​

CamusDB stores a DEFAULT of a column and the condition of a CHECK. A later insert replays both of them. A replay carries no session for the function to report.

The DDL therefore refuses both. It does not accept a schema element that could only fail later:

CREATE TABLE owners (
  id INT64 PRIMARY KEY NOT NULL,
  owner STRING(64) DEFAULT(current_user())     -- refused
);

CREATE TABLE orders (
  id INT64 PRIMARY KEY NOT NULL,
  owner STRING(64) NOT NULL,
  CONSTRAINT owner_is_caller CHECK (owner = current_user())   -- refused
);

A DEFAULT is for a generator that runs for each row, such as gen_id() and now(). Write the value of the session from the statement instead:

INSERT INTO orders (id, owner) VALUES (gen_id(), current_user());

is_superuser() needs no privilege​

The function answers for the session of the caller only. It answers for no other session.

A caller can already learn the same fact in another way. That caller runs a statement that needs a superuser, and it reads whether CamusDB refuses the statement. A direct report therefore discloses nothing new. There is no form of the function that asks about another user.

  • Functions for the other categories.
  • Authentication And Authorization for the users and the grants.
  • Views. The body of a view may call these functions. CamusDB takes the snapshot of the session from the statement of the caller, at every position where it expands the body.