February 2020

I have read on line about XS$NULL over the years and particularly the documentation that states that it has no privileges. The documentation states the following: An internal account that represents the absence of a user in a session. Because....[Read More]

Posted by Pete On 17/02/20 At 01:09 PM

Today’s video is a quick look at online datafile moves in container databases (CDBs) and pluggable databases (PDBs).

If you’ve used this functionality in a non-CDB database, it’s going to look familiar, with a PDB-specific gotcha.

These articles discus moving and renaming files.

The semantics of comparing character columns of different types can lead to some confusion, so before I get into the main body of this note here’s a little test based on a table with one row:

create table t1(c2 char(2), c3 char(3), vc2 varchar2(2), vc3 varchar2(3));

insert into t1 values ('XX','XX','XX','XX');
commit;

select count(*) c2_c3   from t1 where c2 = c3;
select count(*) c2_vc3  from t1 where c2 = vc3;
select count(*) c3_vc2  from t1 where c3 = vc2;
select count(*) c3_vc3  from t1 where c3 = vc3;

I’ve inserted one row, using the same value for every single column; then I’ve been counting the row(s) where various pairs of columns match. Which (if any) of the four queries return the value 1 and which (if any) return the value zero ?

Oracle 11g introduced the abilty to control the behaviour of the dbms_stats package by setting preferences on the database, schema, and table level. These affect the way dbms_stats goes about doing its work. This feature has been extensively documented, I found the post by Maria Colgan exceptionally good at explaining the mechanism.