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Consider the following aggregate operators described in 3: let select = Seqmap let where = Seqfilter Here we have renamed the operations in the F# Seq module to correspond to more standard database query terminology: the select operator is defined as a transform operation, since in a selection we are taking sequence elements and mapping (often narrowing) them to new values Similarly, the where operator is defined as a filter applied on a sequence that takes an 'a -> bool predicate to filter out the desired elements You can use these aggregate operators in a straightforward manner to query and transform in-memory data The only other piece you need is the glue that will make the query and transform operators work together: the standard pipe operator (|>).

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6 when others 7 then 8 -- call some log_error() routine 9 null; 10 end; 11 / SP2-0804: Procedure created with compilation warnings ops$tkyte%ORA11GR2> show errors procedure some_proc Errors for PROCEDURE P: LINE/COL ERROR -------- ----------------------------------------------------------------1/1 PLW-05018: unit SOME_PROC omitted optional AUTHID clause; default value DEFINER used 6/8 PLW-06009: procedure "SOME_PROC" OTHERS handler does not end in RAISE or RAISE_APPLICATION_ERROR

So, if you include WHEN OTHERS in your code and it is not followed by a RAISE or RAISE_APPLICATION_ERROR, be aware that you are almost certainly looking at a bug in your developed code, a bug placed there by you.

Recall that this operator simply flips the order of its arguments; being an infix operator, it feeds the left-side argument into the function on the right This is useful, because the argument to the function is seen before the function itself, propagating important typing information into the function For instance, given a string * int * string array, representing the name, age, and department of various employees, you can select those names that start with letter R as follows: let people = [| ("Joe", 27, "Sales"); ("Rick", 35, "Marketing"); ("Mark", 40, "Sales"); ("Rob", 31, "Administration"); ("Bob", 34, "Marketing") |] let namesR = people |> select (fun (name, age, dept) -> name) |> where (fun name -> nameStartsWith "R") Note that the types of name, age, and dept have been inferred from people, and no type annotation is necessary.

The difference between the two blocks of code, one with a WHEN OTHERS exception block and one without, is subtle, and something you must consider in your applications. Adding an exception handler to a block of PL/SQL code can radically change its behavior. A different way to code this one that restores the statement-level atomicity to the entire PL/SQL block is as follows: ops$tkyte%ORA11GR2> begin 2 savepoint sp; 3 p; 4 exception 5 when others then 6 rollback to sp; 7 dbms_output.put_line( 'Error!!!! ' || sqlerrm ); 8 end; 9 / I fired and updated 1 rows I fired and updated 1 rows Error!!!! ORA-02290: check constraint (OPS$TKYTE.SYS_C0018095) violated PL/SQL procedure successfully completed. ops$tkyte%ORA11GR2> select * from t; no rows selected ops$tkyte%ORA11GR2> select * from t2; CNT ---------0

Finding those people who work in sales and are older than 30 years old is also straightforward: > let namesSalesOver30 = people |> where (fun (_, age, _) -> age >= 30) |> where (fun (_, _, dept) -> dept = "Sales") |> select (fun (name, _, _) -> name);; val namesSalesOver30 : seq<string> > namesSalesOver30;; val it : seq<string> = seq ["Mark"].

Caution The preceding code represents an exceedingly bad practice. In general, you should neither catch a

WHEN OTHERS nor explicitly code what Oracle already provides as far as transaction semantics is concerned.

In the previous section, we used alternative names such as select and where for some standard F# operations such as Seqmap and Seqfilter This is for illustrative purposes to show the connection between these operators and SQL-like querying In most F# code, you should just continue to use the standard F# operators from the Seq module Besides the restriction (filter/where) and projection (map/select) operators, the Seq module contains many other useful functions, many of which were described in 3, and you can easily define further operators For instance, you can define sorting over sequences by using sorting over a more concrete data structure: let sortBy comp seq = seq |> Seqto_list |> Listsort comp |> Seq.

Here, by mimicking the work Oracle normally does for us with the SAVEPOINT, we are able to restore the original behavior while still catching and ignoring the error. I provide this example for illustration only; this is an exceedingly bad coding practice.