Selectable Procedures
Selectable stored procedures usually retrieve data from a database, returning an arbitrary number of rows to the caller.The caller receives the output one row at a time from a row buffer that the database engine prepares for it.
Selectable procedures can be useful for obtaining complex sets of data that are often impossible or too difficult or too slow to retrieve using regular DSQL SELECT
queries.Typically, this style of procedure iterates through a looping process of extracting data, perhaps transforming it before filling the output variables (parameters) with fresh data at each iteration of the loop.A [fblangref50-psql-suspend] statement at the end of the iteration fills the buffer and waits for the caller to fetch the row.Execution of the next iteration of the loop begins when the buffer has been cleared.
Selectable procedures may have input parameters, and the output set is specified by the RETURNS
clause in the header.