COLLECT INTO inside a Cursor Definition?

I have been programming in PL/SQL since 1993, more or less continuously (I’ve just realized that it’s exactly half of my life until now), so I know the PL/SQL syntax quite well.
So when I saw the following piece of code a few days ago, I was willing to bet it would not compile:

declare
    v_number_array sys.odcinumberlist;
begin
    for v_rec in (select rownum as num
                  bulk   collect
                  into   v_number_array
                  from   dual
                  connect by level < = 5)
    loop
        dbms_output.put_line(v_rec.num);
    end loop;
end;

(more...)

Excessive Locking when Dropping a Table in 11g

I tried to drop a table today and failed due to “ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired”.
That was weird because I knew that nobody had been using this table for months, and that the table had no enabled foreign keys.
A quick investigation revealed the cause – the DROP TABLE operation tried to lock another table (in the quite aggressive “Share” mode) that was referenced by a (more...)

A Single Query with Many Filter Combinations – Part 3

In a recent post I suggested a way to write a single SQL query that filters a table by one or more of several columns.
Here is the query from that post:

select * from employees where rowid in (
  select rid from (
    select rowid rid from employees where department_id = :department_id
    union all
    select rowid rid from employees where job_id = :job_id
    union all
    select rowid rid from employees where manager_id = :manager_id
     (more...)

A Single Query with Many Filter Combinations – Part 2

In the previous post I suggested a way to write a single SQL query that filters the EMPLOYEES table (as an example) by one or more of the following columns: DEPARTMENT_ID, JOB_ID, MANAGER_ID and LAST_NAME.

Here is the query from the previous post:

select * from employees where rowid in (
  select rid from (
    select rowid rid from employees where department_id = :department_id
    union all
    select rowid rid from employees where job_id  (more...)

A Single Query with Many Filter Combinations

Let’s assume the EMPLOYEES table (from the HR schema) contains many records, and we want to write an (efficient) SQL query that filters it by one or more of the following columns: DEPARTMENT_ID, JOB_ID, MANAGER_ID and LAST_NAME.
For example:

  • in one execution we may want to get all the employees with DEPARTMENT_ID = 80
  • in a second execution all the employees that their LAST_NAME is King
  • in a third execution all the employees (more...)

Constraint Optimization Summary

This is the last part of a series about Constraint Optimization.
In this post I’ll summarize the conclusions from the previous parts.

When we add a constraint to an existing table, there are two aspects that are worth taking into consideration:

Duration

When the table contains a significant number of rows, adding a constraint may take a lot of time. In some cases Oracle applies a very nice optimization that can reduce this time to (more...)

Adding a Unique Constraint in an Online Way

Note: unlike most of my posts, this one assumes using Enterprise Edition

I have a table t and I want to add a unique constraint on one of its columns – c1.

The Offline Way

The straightforward and most simple way to do it is using a single alter table statement:

SQL> alter table t add constraint c1_uk unique (c1);

Table altered.

By default, Oracle creates in this operation a unique constraint (named c1_uk) and (more...)

Fast but Offline, or Online but Slow?

The Constraint Optimization series:


In the previous parts of this series I showed that Oracle does a nice optimization – that may save (more...)

EBR – Part 5: Explicit Actualization of Dependent Objects

This is part 5 of a post series about EBR.
In part 1 we created the baseline model and code – a table (PEOPLE) and two packages (PEOPLE_DL and APP_MGR).
In part 2 we saw that even a simple change – a package body compilation – can be dangerous in a busy system.
In part 3 we learned about editions and how they can be used for solving the problems described in part 2, so (more...)

EBR – Part 4: Invalidation and Actualization of Dependent Objects

This is part 4 of a post series about EBR.
In part 1 we created the baseline model and code – a table (PEOPLE) and two packages (PEOPLE_DL and APP_MGR).
In part 2 we saw that even a simple change – a package body compilation – can be dangerous in a busy system.
In part 3 we learned about editions and how they can be used for solving the problems described in part 2, so (more...)