rspec/rules/S2564/plsql/rule.adoc

== Why is this an issue?

The performance of DML queries in loops can be improved by placing them in a ``++FORALL++`` statement. This way, queries will be sent in bulk, minimizing the number of context switches between PL/SQL and SQL.


=== Noncompliant code example

[source,sql]
----
SET SERVEROUTPUT ON

CREATE TABLE largeTable(
  foo VARCHAR2(42)
);

BEGIN
  FOR i IN 1 .. 100000 LOOP
    INSERT INTO largeTable VALUES('bar' || i); -- Non-compliant
  END LOOP;
END;
/

SET TIMING ON
DECLARE
  TYPE largeTableRowArrayType IS TABLE OF largeTable%ROWTYPE;
  largeTableRowArray largeTableRowArrayType;
BEGIN
  SELECT * BULK COLLECT INTO largeTableRowArray FROM largeTable;

  EXECUTE IMMEDIATE 'TRUNCATE TABLE largeTable';
  FOR i IN largeTableRowArray.FIRST .. largeTableRowArray.LAST LOOP
    INSERT INTO largeTable (foo) VALUES (largeTableRowArray(i).foo); -- Non-compliant
  END LOOP;
END;
/
SET TIMING OFF

DROP TABLE largeTable;
----


=== Compliant solution

[source,sql]
----
SET SERVEROUTPUT ON

CREATE TABLE largeTable(
  foo VARCHAR2(42)
);

BEGIN
  FOR i IN 1 .. 100000 LOOP
    INSERT INTO largeTable VALUES('bar' || i); -- Non-compliant
  END LOOP;
END;
/

SET TIMING ON
DECLARE
  TYPE largeTableRowArrayType IS TABLE OF largeTable%ROWTYPE;
  largeTableRowArray largeTableRowArrayType;
BEGIN
  SELECT * BULK COLLECT INTO largeTableRowArray FROM largeTable;

  EXECUTE IMMEDIATE 'TRUNCATE TABLE largeTable';
  FORALL i IN largeTableRowArray.FIRST .. largeTableRowArray.LAST
    INSERT INTO largeTable (foo) VALUES (largeTableRowArray(i).foo); -- Compliant

  INSERT INTO largeTable (foo) VALUES ('baz'); -- Compliant, not in a loop
END;
/
SET TIMING OFF

DROP TABLE largeTable;
----

ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Use "FORALL" instead of this DML query in a loop.


endif::env-github,rspecator-view[]