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This page explains the small example in file examples/rara.cpp.
The program rara.cpp accepts the following command line arguments (in fixed order)
examples/rara data-dir query-conditions [column-to-print [column-to-print ...]]For example, after running 'make check', one can issue the following command
examples/rara tests/tmp/t1 "c between 10 and 20"and see the following output
SELECT count(*) FROM tests/tmp/t1 WHERE c between 10 and 20 --> 22The next command
examples/rara tests/tmp/t1 "c between 10 and 20" cproduces the following output
SELECT c FROM tests/tmp/t1 WHERE c between 10 and 20 --> c (with counts) 10, 2 11, 2 12, 2 13, 2 14, 2 15, 2 16, 2 17, 2 18, 2 19, 2 20, 2
// construct a data partition from the given data directory. ibis::part apart(argv, static_cast<const char*>(0));This statement creates an ibis::part object that encapsulates a data partition. The second nil pointer is required because there is another constructor that takes a single string but performs a very different function.
// create a query object with the current user name. ibis::query aquery(ibis::util::userName(), &apart);This statement creates an ibis::query object which represent our query. A FastBit query is always associated with a data partition.
// assign the query conditions as the where clause. int ierr = aquery.setWhereClause(argv);A query object is required to have a where clause (query conditions) before being evaluated. This function returns 0 to indicate success and a negative number to indicate error. This is often the case when an integer is returned from a FastBit function.
ierr = aquery.setSelectClause(sel.c_str());If any column to print is specified on the command line, they are concatenated together into a single string (named sel in rara.cpp). The pointer to the characters is passed to setSelectClause to be recorded as a part of the query.
ierr = aquery.evaluate(); // evaluate the queryThe primary function to evaluate a query is ibis::query::evaluate. This function evaluate the query conditions and identify the records that satisfy the conditions. In some cases, it may be faster to use ibis::query::estimate to get an approximate answer first.
std::cout << aquery.getNumHits();After the function ibis::query::evalaute is called, one may find out how many records satisfy the query conditions by calling ibis::query::getNumHits.
aquery.printSelected(std::cout);If a select clause was successfully set, the function ibis::query::printSelected will print the columns of the selected records to standard output.
The file examples/rara.cpp contains additional code for error checking and optional command-line arguments. The Doxygen documentation of the file is available on-line.