Example:

SELECT * FROM emp
WHERE emp_no IN(1,2,3,4,5......1000);

I needed this because I was given a long list of values (around 500 values) and I need to fetch records in a table using that data. It would be easy if I can insert it first into a temp table and then join. Unfortunately, I only have read rights on the database so I need to use the IN condition. But I got concerned because in Oracle 7 and 8i releases, the maximum number of values you can put inside IN is a maximum of 255 (one byte).

Note:

Take note that the IN(SUBQUERY) does not have limitations because that’s essentially a join.

Example:
SELECT * FROM emp
WHERE emp_no IN(SELECT emp_no FROM dept_emp);

However as part of my best practices, I make sure that the results of the IN subquery is either one or none for optimal performance (not applicable in some instances).

Syntax


set define off


Oh yes, that’s just one line that will solve my misery. Well, it’s all about my ignorance. To turn back on, then do the opposite as below.

Syntax


set define on


WITH Clause Syntax

WITH
 alias_name         -- alias for the aggregate_query
AS
 (aggregate_query_here)
SELECT...            -- Beginning of the query main body

It should be noted that multiple aggregate queries can be defined in the WITH clause as below.

WITH
 alias_name1
AS
 (agg_query1) ,
 alias_name2
AS
 (agg_query2)
SELECT...

When using subquery factoring, think of the aggregate_query as an in-line view. Actually, it is a view but a temporary one. Instead of creating a permanent view accessible in the database, you are creating a temporary one exclusively used by your main query.

Usage

I primarily use this in creating adhoc queries, reports and extractions. Of course, you can just create a view to accomplish this task. However, there are times wherein you are not allowed to create additional objects in the database for one reason or another. In that case, this subquery optimization comes very handy.

Caveat

You can’t use this inside Oracle Forms. It also doesn’t work inside stored procedures or anything with PL/SQL in it. At least I’m talking about until 11g.

Syntax #1


CASE [ expression ]
WHEN condition_1 THEN result_1
WHEN condition_2 THEN result_2
...
WHEN condition_n THEN result_n
ELSE result
END


Example


SELECT last_name, commission_pct,
(CASE commission_pct
WHEN 0.1 THEN ‘Low’
WHEN 0.15 THEN ‘Average’
WHEN 0.2 THEN ‘High’
ELSE ‘N/A’
END ) Commission
FROM employees ORDER BY last_name;


Syntax #2


CASE
WHEN [ condition_1 ] THEN result_1
WHEN [ condition_2 ] THEN result_2
...
WHEN [ condition_n ] THEN result_n
ELSE result
END


Example


SELECT m.paper_type ,
m.paper_brand ,
m.paper_grammage,
m.paper_width ,
m.paper_length ,
m.paper_stock_no,
(
CASE
WHEN NVL(smc.qty_reserved_onhand,0) != NVL(st.sum_qty_r_oh,0) THEN 'QROH NOT TALLY'
WHEN NVL(smc.qty_reserved_incom,0) != NVL(st.sum_qty_r_incom,0) THEN 'QRINC NOT TALLY'
WHEN NVL(smc.ton_reserved_onhand,0) != NVL(st.sum_ton_r_oh,0) THEN 'TROH NOT TALLY'
WHEN NVL(smc.ton_reserved_incom,0) != NVL(st.sum_ton_r_incom,0) THEN 'TRINC NOT TALLY'
END
) ERROR_MESSAGE
from paper_stock_master m


Personally, I use Syntax #2 most of the time. I don’t know why but maybe it just happened that I find it more suitable to use in the situations that I needed the CASE statement.

Difference Between DECODE and CASE WHEN

The most fundamental difference between the two oracle statements is that in DECODE, you are comparing a field or value in a given set of values or fields. It’s actually a shorthand for IF..ELSIF..ELSE statement with the condition all set to equals (=). CASE WHEN is almost the same but you can use any conditional operator (i.e, =,!=, >, >= , <, <=, etc) thereby giving you more freedom and flexibility in writing your code.

In may instances CASE WHEN helped me reduce the number of lines of my codes as well as optimize the performance. On top of that, I no longer need a full pl/sql program with multiple queries and even cursors to be able to provide the result that a simple CASE statement can provide. However CASE, like any other sql commands, is only applicable for certain scenarios. It’s not a magic keyword that will solve/apply to everything. So you have to weigh your options if you need it or not.

Ciao!

All I have to do is copy a whole bunch of files from the ORAHOME folder to ORAHOME\bin. It seems like PL/SQL Developer is hardwired to find the files under the bin folder. It did the trick and my sql editor is now working. I hope it fixes yours too.

Here’s the screenshot of the files I copied. Take note that I copied them instead of just moving so as not to break anything.