SET SESSION AUTHORIZATION(7) SQL Commands SET SESSION AUTHORIZATION(7)NAME
SET SESSION AUTHORIZATION - set the session user identifier and the current user identifier of the current session
SYNOPSIS
SET [ SESSION | LOCAL ] SESSION AUTHORIZATION username
SET [ SESSION | LOCAL ] SESSION AUTHORIZATION DEFAULT
RESET SESSION AUTHORIZATION
DESCRIPTION
This command sets the session user identifier and the current user identifier of the current SQL-session context to be username. The user
name may be written as either an identifier or a string literal. The session user identifier is valid for the duration of a connection;
for example, it is possible to temporarily become an unprivileged user and later switch back to become a superuser.
The session user identifier is initially set to be the (possibly authenticated) user name provided by the client. The current user identi-
fier is normally equal to the session user identifier, but may change temporarily in the context of ``setuid'' functions and similar mecha-
nisms. The current user identifier is relevant for permission checking.
The session user identifier may be changed only if the initial session user (the authenticated user) had the superuser privilege. Other-
wise, the command is accepted only if it specifies the authenticated user name.
The SESSION and LOCAL modifiers act the same as for the regular SET [set(7)] command.
The DEFAULT and RESET forms reset the session and current user identifiers to be the originally authenticated user name. These forms are
always accepted.
EXAMPLES
SELECT SESSION_USER, CURRENT_USER;
current_user | session_user
--------------+--------------
peter | peter
SET SESSION AUTHORIZATION 'paul';
SELECT SESSION_USER, CURRENT_USER;
current_user | session_user
--------------+--------------
paul | paul
COMPATIBILITY
SQL99
SQL99 allows some other expressions to appear in place of the literal username which are not important in practice. PostgreSQL allows iden-
tifier syntax ("username"), which SQL does not. SQL does not allow this command during a transaction; PostgreSQL does not make this
restriction because there is no reason to. The privileges necessary to execute this command are left implementation-defined by the stan-
dard.
SQL - Language Statements 2001-04-21 SET SESSION AUTHORIZATION(7)
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SET TRANSACTION(7) SQL Commands SET TRANSACTION(7)NAME
SET TRANSACTION - set the characteristics of the current transaction
SYNOPSIS
SET TRANSACTION transaction_mode [, ...]
SET SESSION CHARACTERISTICS AS TRANSACTION transaction_mode [, ...]
where transaction_mode is one of:
ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED }
READ WRITE | READ ONLY
DESCRIPTION
The SET TRANSACTION command sets the characteristics of the current transaction. It has no effect on any subsequent transactions. SET SES-
SION CHARACTERISTICS sets the default transaction characteristics for subsequent transactions of a session. These defaults can be overrid-
den by SET TRANSACTION for an individual transaction.
The available transaction characteristics are the transaction isolation level and the transaction access mode (read/write or read-only).
The isolation level of a transaction determines what data the transaction can see when other transactions are running concurrently:
READ COMMITTED
A statement can only see rows committed before it began. This is the default.
SERIALIZABLE
All statements of the current transaction can only see rows committed before the first query or data-modification statement was exe-
cuted in this transaction.
The SQL standard defines two additional levels, READ UNCOMMITTED and REPEATABLE READ. In PostgreSQL READ UNCOMMITTED is treated as READ
COMMITTED, while REPEATABLE READ is treated as SERIALIZABLE.
The transaction isolation level cannot be changed after the first query or data-modification statement (SELECT, INSERT, DELETE, UPDATE,
FETCH, or COPY) of a transaction has been executed. See in the documentation for more information about transaction isolation and concur-
rency control.
The transaction access mode determines whether the transaction is read/write or read-only. Read/write is the default. When a transaction is
read-only, the following SQL commands are disallowed: INSERT, UPDATE, DELETE, and COPY FROM if the table they would write to is not a tem-
porary table; all CREATE, ALTER, and DROP commands; COMMENT, GRANT, REVOKE, TRUNCATE; and EXPLAIN ANALYZE and EXECUTE if the command they
would execute is among those listed. This is a high-level notion of read-only that does not prevent all writes to disk.
NOTES
If SET TRANSACTION is executed without a prior START TRANSACTION or BEGIN, it will appear to have no effect, since the transaction will
immediately end.
It is possible to dispense with SET TRANSACTION by instead specifying the desired transaction_modes in BEGIN or START TRANSACTION.
The session default transaction modes can also be set by setting the configuration parameters default_transaction_isolation and
default_transaction_read_only. (In fact SET SESSION CHARACTERISTICS is just a verbose equivalent for setting these variables with SET.)
This means the defaults can be set in the configuration file, via ALTER DATABASE, etc. Consult in the documentation for more information.
COMPATIBILITY
Both commands are defined in the SQL standard. SERIALIZABLE is the default transaction isolation level in the standard. In PostgreSQL the
default is ordinarily READ COMMITTED, but you can change it as mentioned above. Because of lack of predicate locking, the SERIALIZABLE
level is not truly serializable. See in the documentation for details.
In the SQL standard, there is one other transaction characteristic that can be set with these commands: the size of the diagnostics area.
This concept is specific to embedded SQL, and therefore is not implemented in the PostgreSQL server.
The SQL standard requires commas between successive transaction_modes, but for historical reasons PostgreSQL allows the commas to be omit-
ted.
SQL - Language Statements 2010-05-14 SET TRANSACTION(7)