SQL & PL/SQL

SQL and PL/SQL Articles

dwarak.k's picture

Hierarchical queries

articles: 

A relational database does not store data in a hierarchical way. Then how do I get the data in a hierarchical manner? Here we get to know about how to use the hierarchical querying feature which Oracle has given. This article talks about how you can interpret the hierarchical query conceptually and build hierarchical queries catering your needs.

Using hierarchical queries, you can retrieve records from a table by their natural relationship. Be it a family tree or a employee/manager tree or what ever.

Ahysanali M. Kadiwala's picture

Creating a Calendar in a single SQL statement

articles: 

A few days ago, somebody asked if it is possible to write a Calendar in a single SQL statement.

Here you go...

SELECT LPAD( MONTH, 20-(20-LENGTH(MONTH))/2 ) MONTH,"Sun", "Mon", "Tue",
"Wed", "Thu", "Fri", "Sat"
FROM (SELECT TO_CHAR(dt,'fmMonthfm YYYY') MONTH,TO_CHAR(dt+1,'iw') week,
MAX(DECODE(TO_CHAR(dt,'d'),'1',LPAD(TO_CHAR(dt,'fmdd'),2))) "Sun",
MAX(DECODE(TO_CHAR(dt,'d'),'2',LPAD(TO_CHAR(dt,'fmdd'),2))) "Mon",
MAX(DECODE(TO_CHAR(dt,'d'),'3',LPAD(TO_CHAR(dt,'fmdd'),2))) "Tue",
MAX(DECODE(TO_CHAR(dt,'d'),'4',LPAD(TO_CHAR(dt,'fmdd'),2))) "Wed",

Disabling constraints before the import operation

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Some times you need to disable user constraints before doing the import for some user,
for this reason i created a procedure that can be used to disable the constraints before the import,and than use it again to enable the constraints after doing the import,and also this procedure can be used to drop user constraints when needed.

Kevin Meade's picture

Easy XML - a Programming Oriented Approach

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In a previous article I talked about using Natural Oracle Features to get XML data out of an Oracle database, and put data into an Oracle database, without actually having to learn a lot about XML related technologies. Still, there are many who continue to resist using OBJECTS, COLLECTIONS, and INSTEAD-OF-TRIGGERS in their daily work with the Oracle RDBMS. Since the biggest hurdle with XML seems to be parsing it into its component data elements, here is a more programming oriented approach to parsing XML data inside Oracle that should make this crowd happy.

Tuning High-Volume SQL

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Mr and Mrs Oracle at the Supermarket

I was at the supermarket the other day waiting my turn at the checkout behind another guy. The checkout-chick (I'm sure there is a more PC term, I just don't know what it is) just finished scanning his groceries and he asked her to wait until his wife returned with a few last-minute items. I've done it before, so steam didn't start coming out of my ears - yet. Fifteen seconds later she ran up - sorry, sorry - and checked out the last few items, so I wasn't really inconvenienced.

gojko's picture

Catalogue of SQL & PL/SQL Bad Practices

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I have started compiling a list of Oracle PL/SQL and SQL bad practices, with the intention of producing a comprehensive catalogue of common programming errors, that can be used as a check-list for code reviews or given to junior developers so that they can learn from the mistakes of others.

For each bad practice, I provided a list of symptoms in the code, an explanation why it causes problems and a list of preferred solutions. I have also listed exceptions to the rules, when they exist.

Kevin Meade's picture

Dynamic Views, Creating Views based on Variables

articles: 

I have been asked several times recently, how to create "dynamic" views such that a view can be created using "variables". Now I see this question asked on the OraFaq message board, so I thought maybe this is worth posting as an article, so here it is. My answer comes in the form of an Email reply to a friend (why bother to rewrite a prefectly good answer). Please feel free to abuse my answer if you think it deficient, but you better be posting your own alternatives if you do so.

Kevin Meade's picture

Autonomous Transactions: a Poor Mis-Understood Feature

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In short an Autonomous Transaction lets a job, commit some data to the database as an ON-THE-SIDE event, without committing data in the MAIN-EVENT. Sounds useful and it can be. But the Autonomous Transaction can also be dangerous. An Autonomous Transaction is kind of like a teenage daughter (I have two) "Oh DAD! You just don't understand me". A lack of understanding is a foundation for trouble. Maybe we can’t understand our teenagers, but we can understand Autonomous Transactions a little better.

vjain's picture

Building a Dynamic Oracle ETL Procedure

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If you are on Oracle 9i or higher, you have external tables and pipelined table functions available to meet your ETL needs. But in order to utilize these tools in a dynamic ETL environment, you need to design PL/SQL procedures that can support the loading of files dynamically. This article will provide you with one design that has proven to be very robust and scalable.

Art Trifonov's picture

Making Use of Table Functions -- Part II

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In Part I we discussed views, stored procedures, and table functions as the three options of returning record sets from the code stored in the database. In this section I will concentrate on table functions, demonstrating several kinds of solutions that utilize this feature.

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