RDB$GET_CONTEXT()

Note

RDB$GET_CONTEXT and its counterpart RDB$SET_CONTEXT are actually predeclared UDFs. They are listed here as internal functions because they are always present – the user doesn't have to do anything to make them available.

Available in: DSQL, ESQL, PSQL

Added in: 2.0

Changed in: 2.1

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

Result type: VARCHAR(255)

Syntax:

RDB$GET_CONTEXT ('<namespace>', '<varname>')

<namespace>  ::=  SYSTEM | USER_SESSION | USER_TRANSACTION
<varname>    ::=  A case-sensitive string of max. 80 characters

The namespaces: The 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. It contains a number of predefined variables, shown in the table below.

Table 14.3. Context variables in the SYSTEM namespace

`DB_NAME`	Either the full path to the database or – if connecting via the path is disallowed – its alias.
`NETWORK_PROTOCOL`	The protocol used for the connection: `'TCPv4'`, `'WNET'`, `'XNET'` or `NULL`.
`CLIENT_ADDRESS`	For TCPv4, this is the IP address. For XNET, the local process ID. For all other protocols this variable is `NULL`.
`CURRENT_USER`	Same as global `CURRENT_USER` variable.
`CURRENT_ROLE`	Same as global `CURRENT_ROLE` variable.
`SESSION_ID`	Same as global `CURRENT_CONNECTION` variable.
`TRANSACTION_ID`	Same as global `CURRENT_TRANSACTION` variable.
`ISOLATION_LEVEL`	The isolation level of the current transaction: `'READ` `COMMITTED'`, `'SNAPSHOT'` or `'CONSISTENCY'`.
`ENGINE_VERSION`	The Firebird engine (server) version. Added in 2.1.

Return values and error behaviour: If 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 poll 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.

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'))