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Data Retrieval and Modification
Table 4-1. SQL/MP Statements for Data Retrieval and Modification (page 2 of 2)
SQL/MP Statement
UPDATE statement with a cursor
DELETE statement without a cursor
DELETE statement with a cursor
Note. Using a cursor can sometimes degrade a program's performance. A cursor operation
requires the OPEN, FETCH, and CLOSE statements, which increases the number of
messages between the file system and disk process. Therefore, consider not using a cursor if
a single-row SELECT statement is sufficient.
Opening and Closing Tables and Views
NonStop SQL/MP automatically opens and closes tables and views during the
execution of DDL statements, DML statements, and SQL utility operations such as a
LOAD or COPY. NonStop SQL/MP opens a table or view when a host-language
program runs the first SQL statement that refers to the table or view and then closes
the table or view when the program that opened it stops. A program cannot explicitly
open an SQL table or view; however, a program can force NonStop SQL/MP to close a
table using the CLOSE TABLES option of the FREE RESOURCES statement.
By default, NonStop SQL/MP opens partitions of base tables and indexes only if they
are needed by a program. To cause NonStop SQL/MP to open all indexes and
partitions the first time a partition is accessed, use the OPEN ALL option of the
CONTROL TABLE directive.
Note. Using the CONTROL TABLE statement with the OPEN ALL option could increase the
amount of work done by an SQL statement. For efficient performance, use the OPEN ALL
option with the CONTROL TABLE statement only if all these are true:
When all open activity must occur when the program first starts (add a "dummy" call to the
cursor during initialization).
When the object containing the cursor will eventually access all partitions.
When the plan for the cursor is not a parallel plan.
Causes of SQL Error 8204 (Lost Open Error)
SQL error 8204 is sometimes referred to as the "lost open" error. This scenario
explains how this error can occur:
HP NonStop SQL/MP Programming Manual for C—429847-008
Opening and Closing Tables and Views
Description
Updates the values in one or more columns in a set
of rows, one row at a time. Use when you need to
test a column value in a row before you update the
row.
Deletes a single row or a set of rows from a table or
protection view. Use when you do not need to test a
column value in a row before you delete the row.
Deletes a set of rows, one row at a time, from a table
or protection view. Use when you need to test a
column value in a row before you delete the row.
4-2
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