2.17 Open SQL and DB2 CLI
The alternative Open SQL interface can be used with DB2 CLI. This section provides some specific details.
2.17.1 Placeholder Syntax
The placeholder syntax for DB2 CLI is simply:
?
Here is an example:
INSERT INTO PICNICTABLE VALUES(?)
Placeholders are not a portable feature. Different Access Modules use different placeholder syntax.
2.17.2 RWDBDataCallback and Open SQL
The data callback classes can be used with DB2 CLI to insert and fetch data. These classes are useful for very large data that may not fit in memory for a single database call and are described in
Section 15.3, “The Data Callback Classes,” in the
DB Interface Module User’s Guide.
When fetching data, the DB2 CLI requires that the columns bound to a data callback must be at the end of the select list. For example, if two columns of type integer and LOB are selected, the integer must come before the LOB in the select list in order to use a data callback for the LOB column.The DB Access Module for DB2 CLI will fetch only one row on each call to RWDBOSql::fetch().
Multiple rows can be inserted in one call to
RWDBOSql::execute(). The number of rows is determined by the
entries parameter passed to the constructor of a data callback class or an
RWDBTBuffer instance. Please see
Chapter 15, “Using the Open SQL Classes,” in the
DB Interface Module User’s Guide for information about array input.
2.17.2.1 Piece Size Setting
The DB Access Module for DB2 CLI sets the piece size for inserting or fetching data to 32768. This value represents bytes in the case of binary data, and code units in the case of character data.
2.17.2.2 RWDBDataCallback::getLength()
When inserting data using data callbacks, DB2 CLI does not require the length of the data being inserted. Therefore, the method RWDBDataCallback::getLength() does not need to be overridden in derived classes.
2.17.2.3 Stored Procedures and RWDBDataCallback
Stored procedure execution is not supported with the data callback classes.
2.17.3 Stored Procedures and Open SQL
Standard DB2 CLI stored procedure invocation syntax can be used when executing stored procedures with
RWDBOSql.
RWDBOSql myOpenSqlObject("{ CALL myStoredProc(?, ?) }", RWDBOSql::Procedure);
In this example, myStoredProc is the name of the stored procedure, and ? characters are the placeholders for the parameters to be passed to the stored procedure. Note the provided hint RWDBOSql::Procedure.
RWDBOSql myOpenSqlObject("{ ? = CALL myStoredProc(?, ?)}", RWDBOSql::Procedure);
This example uses an additional placeholder to receive the return value of the stored procedure as an OUT parameter. A DB2 stored procedure is allowed to have a return value only of type integer.
Please see
Section 2.17.5.3 for an example that uses
RWDBOSql with stored procedures.
Stored procedure execution is not supported with the data callback classes.
2.17.3.1 Sequence of Fetching Result Sets and Out Parameters
DB2 stored procedures have no requirement regarding the sequence in which result sets and OUT parameters are fetched. Function fetchReturnParams() could be called any time after the stored procedure execution to retrieve the OUT parameters.
However, to make your application portable across different access modules, it is recommended to fetch OUT parameters after completely processing the result sets.
2.17.4 Executing Cancel in Open SQL
Method
RWDBOSql::cancel() can be used either to cancel the current result set or to cancel all pending result sets of the current execution. This method should be called only after the
RWDBOSql object is executed.
Method
RWDBOSql::cancel(RWDBOSql::Current) cancels the current result set and moves the
RWDBOSql to the next available result set, if any.
Method RWDBOSql::cancel(RWDBOSql::All) cancels all the pending result sets. No subsequent results will be available from the current execution after this call has been made.
2.17.5 Open SQL Examples
These examples illustrate how an
RWDBOSql object can be used to:
All statements are based on an employee table
emp. The examples assume an error handler is associated with the connection in use, and don’t check for any errors after calls to the
RWDBOSql object.
The structure of the table emp is:
empno INT NOT NULL
ename VARCHAR(10) NOT NULL
posn VARCHAR(9) NOT NULL
mgr INT NULL
sal NUMERIC(7,2) NOT NULL
dept INT NOT NULL
2.17.5.1 An Open SQL Insert Example
This example shows how to execute an
INSERT statement using
RWDBOSql to insert data into the
emp table.
const size_t NUM_OF_ROWS = 14; //1
RWDBTBuffer<int> empnoBuff(NUM_OF_ROWS), mgrBuff(NUM_OF_ROWS),
deptBuff(NUM_OF_ROWS);
RWDBTBuffer<RWCString> enameBuff(NUM_OF_ROWS), posnBuff(NUM_OF_ROWS);
RWDBTBuffer<RWDecimalPortable> salBuff(NUM_OF_ROWS); //2
empnoBuff[0] = 1;
enameBuff[0] = "ABC XYZ";
posnBuff[0] = "ADMIN";
mgrBuff[0] = 6;
salBuff[0] = "58000.00";
deptBuff[0] = 4; //3
// Populate rest of the rows
RWDBOSql openSql("INSERT INTO emp VALUES(?, ?, ?, ?, ?, ?)",
RWDBOSql::NonQuery); //4
openSql << empnoBuff << enameBuff << posnBuff
<< mgrBuff << salBuff << deptBuff; //5
openSql.execute(cn); //6
long rowsInserted = openSql.rowsAffected(); //7
std::cout << (openSql.isValid() ? "Data insertion successful." //8
: "Data insertion failed.") << std::endl;
if (rowsInserted >= 0) {
std::cout << "Inserted " << rowsInserted << " rows." << std::endl;
}
2.17.5.2 Open SQL Query Examples
These examples illustrate how an
RWDBOSql object can be used to execute
SELECT queries and retrieve their results. The
SELECT query is executed on the table
emp to retrieve all columns of the table for employees in a particular department.
The first example assumes knowledge of the structure of table
emp (
Section 2.17.5) and hence the schema of the result set returned by the query.
RWDBOSql openSql("SELECT * FROM emp WHERE dept = ?", RWDBOSql::Query); //1
RWDBTBuffer<int> queryDeptBuff; //2
queryDeptBuff[0] = 3; //3
openSql << queryDeptBuff; //4
openSql.execute(cn); //5
const size_t ROWS_TO_FETCH = 5; //6
RWDBTBuffer<int> empnoBuff(ROWS_TO_FETCH), mgrBuff(ROWS_TO_FETCH),
deptBuff(ROWS_TO_FETCH);
RWDBTBuffer<RWCString> enameBuff(ROWS_TO_FETCH), posnBuff(ROWS_TO_FETCH);
RWDBTBuffer<RWDecimalPortable> salBuff(ROWS_TO_FETCH); //7
openSql[0] >> empnoBuff >> enameBuff >> posnBuff >>
mgrBuff >> salBuff >> deptBuff; //8
long rowsFetched = 0;
while ((rowsFetched = openSql.fetch().rowsFetched()) > 0) { //9
for (size_t i = 0; i < rowsFetched; ++i) {
cout << empnoBuff[i] << "\t" << enameBuff[i] << "\t"
<< posnBuff[i] << "\t"; //10
if (mgrBuff.isNull(i)) { //11
cout << "NULL";
}
else {
cout << mgrBuff[i];
}
cout << "\t" << salBuff[i] << "\t" << deptBuff[i] << endl;
}
}
The second example assumes execution of an ad hoc query for which the schema of the result set is not known beforehand.
RWDBOSql openSql("SELECT * FROM emp WHERE dept = ?", RWDBOSql::Query);
RWDBTBuffer<int> queryDeptBuff;
queryDeptBuff[0] = 3;
openSql << queryDeptBuff;
openSql.execute(cn);
const size_t ROWS_TO_FETCH = 5;
RWDBMultiRow mRow(openSql.schema(), ROWS_TO_FETCH); //1
openSql[0] = mRow; //2
long rowsFetched = 0;
while ((rowsFetched = openSql.fetch().rowsFetched()) > 0) { //3
for (size_t row = 0; row < rowsFetched; ++row) {
for (size_t col = 0; col < mRow.numberOfColumns(); ++col) { //4
RWDBValue val = mRow[row][col]; //5
if ( val.isNull() ) { //6
cout << "NULL" << "\t";
}
else {
cout << val.asString() << "\t";
}
}
cout << endl;
}
}
The steps until
RWDBOSql execution are the same as in the previous example.
2.17.5.3 An Open SQL Stored Procedure Example
This example shows how to use an
RWDBOSql object to invoke stored procedure
EmpInDept, fetch result sets, and fetch output parameters.
CREATE PROCEDURE EmpInDept(IN deptno INT, OUT empcount INT)
LANGUAGE SQL
BEGIN
DECLARE c1 CURSOR WITH RETURN TO CALLER FOR
SELECT empno, ename FROM emp WHERE emp.dept = deptno;
DECLARE c2 CURSOR WITH RETURN TO CALLER FOR
SELECT MIN(sal), AVG(sal), MAX(sal) FROM emp WHERE emp.dept = deptno;
SELECT COUNT(*) INTO empcount FROM emp WHERE emp.dept = deptno;
OPEN c1;
OPEN c2;
END
The stored procedure takes a department number as an input parameter and returns the count of employees in that department as an output parameter. It produces two result sets: the first returns a list of employee numbers and names for each employee in that department; the second result set returns a single row with three columns containing the minimum, average and maximum salary of employees in that department.
RWDBOSql openSql ("{CALL EmpInDept(?, ?) }", RWDBOSql::Procedure); //1
RWDBTBuffer<int> dept, empCount; //2
empCount.paramType(RWDBColumn::outParameter); //3
openSql << dept << empCount; //4
dept[0] = 2; //5
openSql.execute(cn); //6
const size_t NUMBER_OF_ROWS = 10;
RWDBTBuffer<int> empNums (NUMBER_OF_ROWS); //7
RWDBTBuffer<RWCString> empNames (NUMBER_OF_ROWS); //8
openSql[0] >> empNums >> empNames; //9
long count = 0;
while ((count = openSql.fetch().rowsFetched()) > 0 ) { //10
for (int row = 0; row < count; row++) {
std::cout << "Employee: " << empNums[row] << ", "
<< empNames[row] << std::endl; //11
}
}
RWDBTBuffer<RWDecimalPortable> minBuff, avgBuff, maxBuff; //12
openSql[1] >> minBuff >> avgBuff >> maxBuff; //13
openSql.fetch(); //14
std::cout << "\nMinimum Salary: " << minBuff[0]
<< "\nAverage Salary: " << avgBuff[0]
<< "\nMaximum Salary: " << maxBuff[0]
<< std::endl; //15
openSql.fetchReturnParams(); //16
std::cout << "Number of Employees in dept " << dept[0] << ": "
<< empCount[0] << std::endl; //17
Execute an INSERT statement, Section 2.17.5.1, “An Open SQL Insert Example.”