Chapter 8. Built-in Scalar Functions

8.1 Context Functions

8.1.1 RDB$GET_CONTEXT()

Available inDSQL, PSQL * As a declared UDF it should be available in ESQL

Result typeVARCHAR(255)

Syntax

RDB$GET_CONTEXT ('<namespace>', <varname>)
 
<namespace> ::= SYSTEM | USER_SESSION | USER_TRANSACTION | DDL_TRIGGER
<varname>   ::= A case-sensitive quoted string of max. 80 characters

Table 8.1.1.1 RDB$GET_CONTEXT Function Parameters
ParameterDescription

namespace

Namespace

varname

Variable name. Case-sensitive. Maximum length is 80 characters

Retrieves the value of a context variable from one of the namespaces SYSTEM, USER_SESSION and USER_TRANSACTION.

The namespacesThe USER_SESSION and USER_TRANSACTION namespaces are initially empty. The user can create and set variables in them with RDB$SET_CONTEXT() and retrieve them with RDB$GET_CONTEXT(). The SYSTEM namespace is read-only. The DDL_TRIGGER namespace is only valid in DDL triggers, and is read-only. It contains a number of predefined variables, shown below.

Return values and error behaviourIf the polled variable exists in the given namespace, its value will be returned as a string of max. 255 characters. If the namespace doesn’t exist or if you try to access a non-existing variable in the SYSTEM namespace, an error is raised. If you request a non-existing variable in one of the other namespaces, NULL is returned. Both namespace and variable names must be given as single-quoted, case-sensitive, non-NULL strings.

8.1.1.1 The SYSTEM Namespace

Context variables in the SYSTEM namespace
CLIENT_ADDRESS

For TCPv4, this is the IP address. For XNET, the local process ID. For all other protocols this variable is NULL.

CURRENT_ROLE

Same as global Section 11.3, CURRENT_ROLE variable.

CURRENT_USER

Same as global Section 11.7, CURRENT_USER variable.

DB_NAME

Either the full path to the database or — if connecting via the path is disallowed — its alias.

ENGINE_VERSION

The Firebird engine (server) version.

EXT_CONN_POOL_ACTIVE_COUNT

Count of active connections associated with the external connection pool

EXT_CONN_POOL_IDLE_COUNT

Count of currently inactive connections available in the connection pool

EXT_CONN_POOL_LIFETIME

External connection pool idle connection lifetime, in seconds

EXT_CONN_POOL_SIZE

External connection pool size

ISOLATION_LEVEL

The isolation level of the current transaction: 'READ COMMITTED', 'SNAPSHOT' or 'CONSISTENCY'.

NETWORK_PROTOCOL

The protocol used for the connection: 'TCPv4', 'WNET', 'XNET' or NULL.

SESSION_ID

Same as global Section 11.1, CURRENT_CONNECTION variable.

SESSION_IDLE_TIMEOUT

Connection-level idle timeout, or 0 if no timeout was set. When 0 is reported the database ConnectionIdleTimeout from databases.conf or firebird.conf applies.

SNAPSHOT_NUMBER

Current snapshot number for the transaction executing this statement. For SNAPSHOT and SNAPSHOT TABLE STABILITY, this number is stable for the duration of the transaction; for READ COMMITTED this number will change (increment) as concurrent transactions are committed.

STATEMENT_TIMEOUT

Connection-level statement timeout, or 0 if no timeout was set. When 0 is reported the database StatementTimeout from databases.conf or firebird.conf applies.

TRANSACTION_ID

Same as global Section 11.6, CURRENT_TRANSACTION variable.

WIRE_COMPRESSED

Compression status of the current connection. If the connection is compressed, returns TRUE; if it is not compressed, returns FALSE. Returns NULL if the connection is embedded.

WIRE_ENCRYPTED

Encryption status of the current connection. If the connection is encrypted, returns TRUE; if it is not encrypted, returns FALSE. Returns NULL if the connection is embedded.

8.1.1.2 The DDL_TRIGGER Namespace

The DDL_TRIGGER namespace is valid only when a DDL trigger is running. Its use is also valid in stored procedures and functions called by DDL triggers.

The DDL_TRIGGER context works like a stack. Before a DDL trigger is fired, the values relative to the executed command are pushed onto this stack. After the trigger finishes, the values are popped. So in the case of cascade DDL statements, when a user DDL command fires a DDL trigger and this trigger executes another DDL command with EXECUTE STATEMENT, the values of the DDL_TRIGGER namespace are the ones relative to the command that fired the last DDL trigger on the call stack.

Context variables in the DDL_TRIGGER namespace
EVENT_TYPE

event type (CREATE, ALTER, DROP)

OBJECT_TYPE

object type (TABLE, VIEW, etc)

DDL_EVENT

event name (<ddl event item>), where <ddl_event_item> is EVENT_TYPE || ' ' || OBJECT_TYPE

OBJECT_NAME

metadata object name

OLD_OBJECT_NAME

for tracking the renaming of a domain (see note)

NEW_OBJECT_NAME

for tracking the renaming of a domain (see note)

SQL_TEXT

sql statement text

🛈︎
Note

ALTER DOMAIN old-name TO new-name sets OLD_OBJECT_NAME and NEW_OBJECT_NAME in both BEFORE and AFTER triggers. For this command, OBJECT_NAME will have the old object name in BEFORE triggers, and the new object name in AFTER triggers.

8.1.1.3 Examples

select rdb$get_context('SYSTEM', 'DB_NAME') from rdb$database
 
New.UserAddr = rdb$get_context('SYSTEM', 'CLIENT_ADDRESS');
 
insert into MyTable (TestField)
  values (rdb$get_context('USER_SESSION', 'MyVar'))

See alsoSection 8.1.2, RDB$SET_CONTEXT()

8.1.2 RDB$SET_CONTEXT()

Available inDSQL, PSQL * As a declared UDF it should be available in ESQL

Result typeINTEGER

Syntax

RDB$SET_CONTEXT ('<namespace>', <varname>, <value> | NULL)
 
<namespace> ::= USER_SESSION | USER_TRANSACTION
<varname>   ::= A case-sensitive quoted string of max. 80 characters
<value>     ::= A value of any type, as long as it's castable
                to a VARCHAR(255)

Table 8.1.2.1 RDB$SET_CONTEXT Function Parameters
ParameterDescription

namespace

Namespace

varname

Variable name. Case-sensitive. Maximum length is 80 characters

value

Data of any type provided it can be cast to VARCHAR(255)

Creates, sets or unsets a variable in one of the user-writable namespaces USER_SESSION and USER_TRANSACTION.

The namespacesThe USER_SESSION and USER_TRANSACTION namespaces are initially empty. The user can create and set variables in them with RDB$SET_CONTEXT() and retrieve them with RDB$GET_CONTEXT(). The USER_SESSION context is bound to the current connection. Variables in USER_TRANSACTION only exist in the transaction in which they have been set. When the transaction ends, the context and all the variables defined in it are destroyed.

Return values and error behaviourThe function returns 1 when the variable already existed before the call and 0 when it didn’t. To remove a variable from a context, set it to NULL. If the given namespace doesn’t exist, an error is raised. Both namespace and variable names must be entered as single-quoted, case-sensitive, non-NULL strings.

🛈︎
Note
  • The maximum number of variables in any single context is 1000.

  • All USER_TRANSACTION variables will survive a ROLLBACK RETAIN (see ROLLBACK Options) or ROLLBACK TO SAVEPOINT unaltered, no matter at which point during the transaction they were set.

  • Due to its UDF-like nature, RDB$SET_CONTEXT can — in PSQL only — be called like a void function, without assigning the result, as in the second example above. Regular internal functions don’t allow this type of use.

Examples

select rdb$set_context('USER_SESSION', 'MyVar', 493) from rdb$database
 
rdb$set_context('USER_SESSION', 'RecordsFound', RecCounter);
 
select rdb$set_context('USER_TRANSACTION', 'Savepoints', 'Yes')
  from rdb$database

See alsoSection 8.1.1, RDB$GET_CONTEXT()