version 1.0.2, 2013-10-19 : changing a part of the intruduction warning
Notes for exam 1Z0-047This document is regrouping my personal notes I took while revising for the 1Z0-047 Oracle certification exam.
This is not a complete review of the exam topics, just the ones I either having hard time to remember or just found interesting to keep track of.
Create Table As Select copies CHECK and NOT NULL constraints but not PU, UK, FK, indexes.
Indexes have their own namespace (different from tables), just as for constraints.
WITH CHECK OPTION prevent rows to be updated/inserted OUTSIDE the view and the update target from getting rows disapear from the view.
To reset or change the value of a sequence, you must recreate it. That’s the only way.
In a WHERE clause,
NOT is evaluated 1st, then
OR (if no parentheses).
In a where clause, the
NOT IN excludes NULL.
Where clause executes before SET clause in an update ⇒ update with no row will not fail if SET has incorrectly formatted values…
NOT NULL constraints cannot be precised in an outline way.
With set operators, you can order by position or by any column of the 1st select list.
MINVALUE defaults to 1
MAXVALUE can be set to < 0 as long as MINVALUE < MAXVALUE
After setting a column to unused, you can reuse its name for another column.
GROUPING function returns 1 for superaggregated rows.
TIMESTAMP WITH TIMEZONE cannot be used as PK, but
TIMESTAMP WITH LOCAL TIMEZONE can.
SAVEPOINT <savepoint_name> (no TO), but
ROLLBACK TO <savepoint_name> (here you have a TO)!
DISTINCT and UNIQUE operators do exactly the same thing in a select clause.
PRIOR is on the side making reference to the parent line.
CREATE DIRECTORY statement do not test the existence of the directory path.
SELECT ROWNUM, * FROM ... will generate an syntax error. You cannot have a column and an a * in the same select clause.
An updatable view cannot be base on hierarchical query.
To disable PK with FK referencing it, use:
ALTER TABLE <table_name> DISABLE PRIMARY KEY CASCADE;
FK needs the referenced columns to be constrained by a UNIQUE constraint (no need to be a PK).
Synonym creation do not require that the target object exists.
ALTER TABLE ... will prevent flashback from working.
Semijoins stand for
AVG(NULL) = NULL != 0
Available pseudocolumns in flashback version query are:
The UNDO_SQL column of the
FLASHBACK_TRANSACTION_QUERY table shows informations required to undo a single SQL statement (and not a whole transaction).
VERSION BETWEEN MINVALUE AND MAXVALUE get all the versions of the select in the time interval (MINVALUE is the minimum timestamp available in flashback operations).
When using a combination of
AS OF and
VERSION BETWEEN, VERSION BETWEEN must be BEFORE AS OF.
You cannot reference subquery’s table aliases in the WHEN condition(s) of a multitable INSERT.
You cannot use NEXTVAL of a sequence in a subquery of a multitable INSERT.
NEXTVAL in a WHEN condition of a multitable INSERT will increment ONE and only ONE time for each line regardless whether the when condition evaluates to true or if a multiple WHEN calls NEXTVAL.
In MERGE statements, DELETE only affect previously updated rows, not inserted or not matching.
TRIM(<string> [<trim_char>] [FROM LEADING|TRAILING|BOTH])
SOUNDEX ⇒ 1st letter + 3 numerics. Don’t forget to use it twice in a comparision.
REMAINDER ⇒ plus proche multiple + !=
You cannot change database TZ if it already has a TIMESTAMP WITH LOCAL TIMEZONE column defined.
5 types of constraints:
TZD = Time Zone Daylight (includes PST, EDT, EST, CST, PDT)
HAVING can preceede a GROUP BY clause. It is not required to follow it.
All columns of a view must have a name assigned.
If you modify a column adding a DEFAULT constraint, the DEFAULT keyword must follow the datatype specification, not preceed it!
You cannot set the DEFAULT value to a column with something taht conflicts with its datatype.
You cannot change the datatype of an already populated column.
To set a column unused:
ALTER TABLE <table_name> SET UNUSED COLUMN <col_name>;
The GROUPING SETS operations combines the resulting row sets with an UNION ALL operation.
ALL_* views list any type of objects in the database, regardless of owner, to which your account has been granted access.
ALL_TAB_PRIV_RECD view list grants on objects for which the user, PUBLIC or enabled role is grantee.
NUMTODSINTERVAL(<number>, 'UNIT_OF_THE_NUMBER_LIKE_MINUTE') The unit of the number must be enclosed by quotes.
To defer an constraint, it must have been created with the
DEFERRABLE option. Then you defer it using
SET CONSTRAINT <constraint_name> DEFERRED;
NVL2 function syntax
NVL2('<column or expression to evaluate>', '<column or expression to return if NOT NULL>', '<column or expression to return if NULL>')
A coumpound query will, by default, return rows sorted accross all the columns, from the left to the right. The only exception is
UNION ALL where the rows will not be sorted.
The result set of an inner query will be nested before the outer query can run.