Usage instructions

Table of Contents Single-threaded vs multi-threaded operation Using PiCO QL SQL queries The rownum column Updating virtual table definitions

Single-threaded vs multi-threaded operation

Users may start PiCO_QL in the same thread as the application (single-threaded) or in a separate thread. In the former case, PiCO_QL has to be compiled with PICO_QL_SINGLE_THREADED flag enabled. Normally pico_ql_serve() returns 101 (SQLITE_DONE).

Using PiCO QL

In production mode (PICO_QL_TEST not defined) PICO QL opens a port at localhost where the SWILL web interface is listening for query requests. Opening a browser at this address presents the query interface. The port number is provided as an argument to pico_ql_serve(). A usual port number is 8080.

SQL queries

SQL queries conform to ANSI SQL92 standard. SQLite relaxes SQL's restriction on the column names that can appear in a SELECT with a GROUP BY clause. This makes it easier to process shared objects nested within other collections as single record set.

The rownum column

Virtual tables representing C++ collections or C multi-element data structures have an extra column, the rownum column. It indexes the position of an element inside a C++ collection or a C multi-element data structure. It can be projected in queries as usual and it can be selected using an equality constraint, e.g. WHERE rownum = 4 selects the fourth element. The rownum column, like the base column, is auto-generated. The rownum column is available with a C++ build ([cpp] argument to parser-generator). Many examples of use are provided in the VRP example case study test query file.

Updating virtual table definitions

Users may update table definitions in the DSL then execute the generator, re-compile, and execute the application.