SQL/MX 2.x Reference Manual (G06.24+, H06.03+)

Metadata Tables
HP NonStop SQL/MX Reference Manual—523725-004
10-30
Overriding System-Defined Default Settings
For some attributes, you can override a default setting by specifying an option within a
statement or command. For example, you can set the transaction isolation level with
the SELECT statement. If you do not enter an option when entering a command or do
not provide some attribute associated with the execution of queries, NonStop SQL/MX
uses a default setting.
This table shows the lowest (1) to highest (6) order of precedence for different methods
of specifying default settings:
Inserting Values Into the SYSTEM_DEFAULTS Table
The insertions do not affect your current session. You must exit and then reenter the
MXCI session for these values to take effect as system-level default settings. In
addition, the insertions do not affect previously compiled modules. You must recompile
these modules for the values to take effect.
Changes you make through the SYSTEM_DEFAULTS table are permanent until
changed by another UPDATE statement or overridden by a CONTROL QUERY
DEFAULT, CONTROL TABLE, SQL statement, or SET TABLE TIMEOUT statement, as
noted in the previous table.
Using the CONTROL QUERY DEFAULT Statement
Execution of the CONTROL QUERY DEFAULT statement does not change the
contents of the SYSTEM_DEFAULTS table and, therefore, affects only the current
session. See CONTROL QUERY DEFAULT Statement on page 2-35.
If an attribute has a value in the SYSTEM_DEFAULTS table and a CONTROL QUERY
DEFAULT statement is issued for that attribute, the value specified by CONTROL
QUERY DEFAULT takes precedence over the value in the SYSTEM_DEFAULTS table
for the current process.
Method of Specifying Default Settings Scope of the Setting When Applied
1. System-defined default settings
(hard-coded)
System-wide Installation
2. Default settings in
SYSTEM_DEFAULTS table
System-wide Compile time or by
reentering the MXCI
session
3. CONTROL QUERY DEFAULT
statement
Current process Compile time or
immediately in the
MXCI session
4. CONTROL TABLE statement Current process Compile time or
immediately in the
MXCI session
5. SQL statement option Current process Compile time or
immediately in the
MXCI session
6. SET TABLE TIMEOUT statement Current process Run time