Open SQL Query Examples
Example 8 – Executing a SELECT query using an RWDBOSql object
These examples illustrate how an
RWDBOSql object can be used to execute
SELECT queries and retrieve their results. The
SELECT query is executed on table
emp and retrieves all columns of the table for employees in a particular department.
The first example assumes awareness of the structure of table
emp (
Open SQL Examples ) and hence the schema of the result set returned by the query.
RWDBOSql openSql("SELECT * FROM emp WHERE dept = $1", 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 = $1", 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 till the execution of the
RWDBOSql are the same as the previous example.
