When most people first start learning to tune SQL, they develop a fascination with this mysterious column on the execution plan called “cost.” What is cost? And how can you use it to tune SQL? So here’s, high level, what… Read More
Autonomous Database Specialist (1Z0-931)
You have to pass exam 1Z0-931 if you want to become an Oracle Autonomous Database specialist, . I just passed the 1Z0-931 exam today, and my source of study material was the autonomous transaction processing labs handbook from a hands-on… Read More
Oracle Network Toubleshooting Guide
I hate troubleshooting Oracle Network Problems the most!!! I would MUCH rather see an ORA-600 error. Because I’ve come across these errors and I know how painful they can be, I’ve set up this little troubleshooting guide that will hopefully… Read More
Why Is My Cursor Not Shared?
Many times, Oracle generates a new cursor for a query that already has a child cursor in the shared pool. When this happens, people often ask the question “why is my cursor not being shared?” Fortunately, there’s an Oracle view… Read More
Summing Interval Data Types
Something I’ve occasionally thought would be really nice is if Oracle had a good way of summing interval data types, much the same way that you can SUM() number data types. Occasionally I’ve designed processes that record start and stop… Read More
How to tell if you have a multi-pass hash join
A hash join can be either an optimal hash join, a one-pass hash join, or a multi-pass hash join. Optimal hash joins – The entire build table fits nicely into memory One-pass hash joins – The build table did not… Read More
Handy trick to avoid ORA-54013: INSERT operation disallowed on virtual columns
In some regards, virtual columns are great: Virtual columns don’t take up physical disk space, which allow for skinnier tables. However, an annoyance with virtual columns is Oracle will give you an ORA-54013 error if you try to insert a… Read More
How to cancel a query in SQL Developer
A common question that user’s of Oracle’s SQL Developer ask is “How can I cancel a query in SQL Developer?” Many times, the reason for this is, out of the box, SQL Developer uses a jdbc “thin” driver. This thin… Read More
What is a “Skinny Table” (aka “Narrow Table” or “Strip Table”)?
A skinny table (also called a “Narrow Table” or a “Strip Table”) is a table that has very few columns and/or very narrow columns. This means the table has an small average row length. You can make a skinny table… Read More
ORA-54012: virtual column is referenced in a column expression
ORA-54012 is caused when you try to create a table where one virtual column is attempting to reference a different virtual column. Oracle has created the restriction of preventing one virtual column from referencing another. This helps to prevent complexities… Read More