DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

Characteristics of the host variable array (HVA):
► The HVA is an array in which each element of the array contains a value for the same
column (one HVA per column)
► The HVA can only be referenced in multi-row FETCH or INSERT
► The HVA is used to receive multiple values for a column on FETCH, or to provide multiple
values for a column on INSERT
► The HVA is supported in COBOL, PL/1, C and C++
3.1.1 Example of usage of multi-row fetch in PL/I
Figure 3-2 shows the declaration of Host Variable Arrays, the declaration of the cursor with
rowset positioning, open cursor and fetch of a rowset of 10 rows in a single SQL statement.
Declare HVAs with 10 elements for each column
DCL COL1(10) CHAR(8);
Each element of the HOST VARIABLE ARRAY
contains a value for the same column
DCL COL2(10) CHAR(8);
DCL COL3(10) BIN FIXED(31);
Declare a CURSOR C1 and fetch 10 rows using a Multi-row FETCH
EXEC SQL
DECLARE C1 CURSOR WITH ROWSET POSITIONING FOR
SELECT * FROM TABLE1;
WITH ROWSET POSITIONING specifies
whether multiple rows of data can be accessed
EXEC SQL OPEN C1;
as a rowset on a single FETCH statement
EXEC SQL
FETCH NEXT ROWSET FROM C1 FOR 10 ROWS
INTO :COL1, :COL2, :COL3; The size of the rowset is not specified on the
DECLARE CURSOR statement, it is done at
.....
FETCH time
Figure 3-2 Usage of multi-row fetch
3.1.2 Example of usage of multi-row insert in PL/I
Example 3-1 shows the statement to insert a rowset of 10 rows into a table with a single SQL
statement.
Example 3-1 Insert 10 rows using host variable arrays for column values
EXEC SQL
INSERT INTO TABLE2
VALUES ( :COL1, :COL2, :COL3)
FOR 10 ROWS ;
.....
When we increase the number of rows processed per multi-row fetch or insert, the size of the
host variable array is increased in the application program and it is processed row by row in
DB2.
32 DB2 UDB for z/OS Version 8 Performance Topics