kwatog & co.

This one has been on my draft for more than a year already so I better fix it up and share. Besides, I find myself more and more googling my site to find my posts instead of searching via the WP admin. Without further ado, here it is..
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As part of hardening your WordPress installation, it is recommended that we change the prefix of our WP tables. In that way, the ‘bad guys’ and script kiddies will have to guess the name of your tables.

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Here’s the MySQL equivalent of Oracle’s NVL and MSSQL/Sybase’s ISNULL functions.

Syntax


IFNULL(expr1,expr2)


Usage

If expr1 is not NULL, IFNULL() returns expr1; otherwise it returns expr2. Take note that IFNULL() returns a numeric or string value, depending on the context in which it is used. I haven’t used it for other data types yet but I reckon it would have the same results. That is to return the same data type as that of expr1. Another important thing to remember is that expr1 and expr2 should have the same data type

WITH clause was introduced in Oracle 9i to provide powerful new syntax for enhancing query performance. It optimizes query speed by eliminating redundant processing in complex queries.

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.

Another oracle sql statement that you may need in order to simplify and optimize your code is the use of CASE statement. Here’s how it is being used.

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!