Fear No SQL
Recently I was asked to look at a problem where a simple query refused to use an index. The table had several million rows in it with a single index on one column populated with 3 values (in my sample the values are A, B, and C.) CREATE TABLE null_test ( col1 NUMBER, col2 NUMBER,…
Part 1Part 2 I’ve continued to enjoy this little puzzle and trying to find different ways of solving it. I’ve used the CONNECT BY clause to unpivot words into lists of letters but in this article I’ll show a more direct recursion on the word and then wrap up the series with the smallest and…
Part 1Part 3 In my last post I solved the task of finding words that can be typed with alternating hands by using collections, match recognize, and analytics. I closed with the comment that I was confident MODEL could be used to solve it too; but at the time I wasn’t sure how to do…
Part 2Part 3 Yesterday, a coworker asked me a question just out of curiosity: “How would you determine which words can be typed with alternating hands?” He then added an additional criteria that he’d like to find the words that ended on the left hand (presumably, so you could press space or enter with the…
Previously, I’ve shown how to use a user-defined aggregate to process numeric values; but they can be used for text as well. Recently I was tasked with importing some denormalized text data and aggregating into a consistent form. The source data consisted of many rows holding identifiers, multiple comma-separated values (CSV,) and several other fields.…
A common occurrence in sql is to aggregate text values into a larger, delimited value. It can also occur that you have a delimited value and you want treat it as a collection to pull data out of it process each of the sub-values. Oracle has a built-in function LISTAGG to aggregate text values into…
I’ve been asked this question in various forms and forums over the years and the askers are often surprised when I tell them there is more than one way to answer that question. Furthermore, each method yields a different but not necessarily wrong answer! First, let’s take a simple, maybe even obvious method: SELECT avg_row_len…
TEMP can be a difficult resource to manage in mixed workload environments. You might have sufficient space to run a few big sorts or aggregates; or maybe you have enough space to run lots of concurrent sessions each of which consumes a little bit. But then you get the occasional overlap and there just isn’t…
A fairly common question I get as a DBA is tracking down which sessions are blocking others. Fortunately the v$session view has the blocking session (as of 10.1) and instance of that session (as of 10.2) included. Since a blocker could itself be blocked by yet another session, I use a hierarchical query to determine…
https://docs.oracle.com/en/database/oracle/oracle-database/18/index.html Definitely interested in looking into the json functionality https://docs.oracle.com/en/database/oracle/oracle-database/18/adjsn/changes.html#GUID-8C9B00DD-45D8-499B-919C-8632E034B664 and digging in more with analytic views https://docs.oracle.com/en/database/oracle/oracle-database/18/sqlrf/Changes-in-This-Release-for-Oracle-Database-SQL-Language-Reference.html#GUID-9D1C204A-91C3-4B8D-A882-374F78118862
The servers of your Oracle databases will be of either Big or Little endianness. That is, the ordering of bytes within values. For the most part, the Oracle APIs insulate your code from ever needing to know which method your system is using. However, there are cases, such as transportable tablespaces or working with binary…
In my previous post I showed how to use the MAP member functions to compare two objects of the same class. The MAP functions are useful when an object can be meaningfully represented and compared by a single value, especially if that value might provide functionality or meaning itself (such as the triangle area mapping…
If you have 2 instances of an object, A and B, you might want to compare them: is A > B or B > A? By default, two instances can’t be compared for greater or lesser value, only for equality. Where equality is determined by checking each attribute of each instance in order and comparing…
When an object type is instantiated (i.e. assigned a non-null value) it will execute initialization code. This initialization code is called a CONSTRUCTOR function. Every object type includes an implicit constructor which simply assigns values to the object attributes according to the values provided in the object assignment. For example: CREATE OR REPLACE TYPE simpleobject…
A lot of developers see Object Types as confusing, esoteric, or simply unrelated to their SQL work. To be fair, some objects can be quite complex and some of the data cartridge (ODCI) features will never find a home in some developer’s applications. But, that still shouldn’t preclude an examination of some of the fundamentals…
The MERGE command in Oracle is a great tool for modifying data in a table; efficiently solving the old problem of insert collisions and updates of non-existent rows. Most of the time we use it becaue it “just works.” But, what really goes on when you issue a merge? In particular, which triggers fire? How…
One of the interesting features of Oracle is if an entry in an index would only have nulls in it, then that entry isn’t created. A simple test can verify this assertion. SQL> CREATE TABLE null_test 2 ( 3 id INTEGER NOT NULL, 4 dummy_string VARCHAR2(10) 5 ); Table created. SQL> INSERT INTO null_test(id, dummy_string)…
I ran into an interesting bug in some code today due to a math error which caused CHR() to be called with non-integer input values. According to the Oracle documentation, this is perfectly acceptable; but it doesn’t make much sense. Unfortunately, the documentation doesn’t specify what should happen for such inputs. This ambiguity is the…
When I wrote my article on Oracle passwords I included a small, limited implementation of the PBKDF2 algorithm in order to illustrate the 12c hashing methodology. Here I’m publishing a fuller implementation with parameters for determining the derived key length, number of hashing iterations, and a choice of hashing methods (SH1, SH256, SH384, or SH512.) …
Added section on 11g and 12c SQLNET.ORA parameters. WordPress article here. A pdf of this article can be downloaded from my dropbox here.
Recently I was asked how to bind an R variable to a SQL statement executed with ROracle. In this case it wasn’t a simple “select * from table where x = :b1 and y = :b2.” You can do those quite easily with a data.frame with only one row in it using dbGetQuery(connection, sqlstatement, data.frame)…
In my previous two posts I showed how to setup a schema for the TPC-H tables and test data. A related test system called the Star Schema Benchmark (SSB) from Pat O’Neil, Betty O’Neil, and Xuedong Chen at the University of Massachusetts at Boston alters the TPC-H structures to create a warehousing data model. The…
In my previous post I showed how to set up data loads for the TPC-H test data. All of the steps provided should work regardless of the data volume. However, for large data sets you may want to parallelize the data generation and data import in order to speed up the process. The user, directory,…
While Oracle has their own SCOTT, SH, OE, HR, etc. sample schemas, it’s often useful to have the ability to scale data volumes for different experiments. The TPC-H schema and sample data sets provide a convenient means of doing so. They are especially helpful in scenarios such as this, blogging, where readers may have a…
12.2.0.1 has been released for on premises installation. It’s only available for Linux and Solaris so far, but that’s good enough to get some test installations started. http://www.oracle.com/technetwork/database/enterprise-edition/downloads/index.html
Recently I encountered an interesting situation where a job has been running successfully for months and then one day it suddenly started failing every time with an ORA-06502: PL/SQL: numeric or value error. The same error can also manifest itself in bulk operations with ORA-06502: PL/SQL: numeric or value error: Bulk Bind: Truncated Bind. The…
The ASH charts in OEM are great utilities for getting a quick summary of your system’s activity. However, these results can be misleading because of how the data is represented on screen. First, ASH is data is collected by sampling so it’s not a complete picture of everything that runs. Another thing to consider is…
Oracle offers several methods for finding the name of a database. More significantly, 12c introduces new functionality which may change the expected value from some of the old methods due to the multi-tenant feature. Here are 11 methods for finding the name of a database. SELECT ‘ora_database_name’ method, ora_database_name VALUE FROM DUAL UNION ALL SELECT…
Several years ago I wrote a small summary of the Oracle password hashing and storage for versions up to 11g. Today I’ve completed my update of that article up to 12.1.0.2, including code to mimic generation of passwords given the appropriate salts. The initial publication is in PDF format, I may convert and reformat it…
I’ve used this tool for a wide variety of other parsing projects. One of the interesting tuning techniques I used was to pull the clob apart into 32K varchar2 chunks. It is possible to split the clob directly using the DBMS_LOB package or through the overloaded SQL functions; but clobs are expensive objects. Varchar2 variables…
I live in Ohio which is fairly stable as far as earthquakes go; but I have coworkers and friends that live in other, more quake-prone areas of the country. So, sometimes I like to look up what’s going on in those areas. Naturally, I decided to see how I could use Oracle features to assist…
I let this project sit on the back burners for too many months but tonight finally got around to cleaning it up and getting it out for people to use. Do note, the authentication is a little different and hence, not compatible with prior versions. While I don’t like breaking compatibility, it was a necessary…
If A < B and B < C then A < C Right? We all know the transitive rule… all of us except the Oracle optimizer. Here’s a seasonal example to illustrate how the Optimizer changes it’s methods based on seemingly trivial options. Let’s say I bake 10 types of cookies and then I want…
I finished “Oracle PL/SQL Performance Tuning Tips & Techniques” by Michael Rosenblum and Paul Dorsey today. I recommend it as a lesson, a reference, and an inspiration for things to try. Steven Feuerstein still gets the nod as the “go to” for first learning how to use pl/sql; but this book has great examples for…
I’m in the process of updating my OID package from last year to version 2.0. The new version will include a significant change in API but will also include more functionality, in particular, support for TNS aliases. I’m also changing the way exceptions are raised as well as improving the efficiency of searches. Along the…
11gR2 introduced the DBMS_PARALLEL_EXECUTE package. The basic idea behind it is you divide some large task into smaller chunks and then execute all the chunks in parallel. The API and the examples in the Oracle Documentation might lead one to believe the package can only be used to split large SQL statements into parallel chunks.…
I have an Oracle Express Edition (XE) database running on almost every pc in my home. It’s not so numerous that I can’t manage them by manipulation of TNSNAMES.ORA; but I always thought it would be nice to manage them centrally via LDAP service name lookup. Unfortunately Oracle Internet Directory (OID) licensing is included with…
A not-uncommon request I hear is to explain when the contents of a view are updated. Sometimes this will be to explain the difference between a “view” and a “materialized view.” I like analogies as a tool to help describe what I’m trying to say. I wear glasses. Querying through a view is like looking…
One of the new features of 12c is the ability to create varchar2 columns up to 32k in size. This feature isn’t enabled by default. You have to put the db into upgrade mode, set max_string_size to EXTENDED and restart the db. However, once you do that, then the big strings are just like normal…
I’m disappointed with the container licensing. Seems odd to publish with a “consume more resources than needed” option turned on. Of course, people will want to buy the containers to take full advantage of their hardware. So I guess I can understand the sales model but from a branding perspective publishing with the brakes locked…
Oracle supports several methods for constructing Interval types including the NUMTODSINTERVAL and NUMTOYMINTERVAL functions. As their names imply, these simply convert a number of some units (day,hour,minute, second or month,year respectively) into an interval type. There is however no built-in method for reversing the process. The two functions below fill in this hole. I hope…
First day was unintentionally APEX heavy for me. Not that that’s a bad thing, just sort of surprising to me in hindsight. Saw some really neat apps and ideas with HTML5 and dynamic actions. Also saw some new tools I’ll be checking out to make my own development more productive like aptana studio and apexlib.…
Just found this data yesterday, not sure when or how it got into the real table. Ironically the column that is corrupt is the mod_date which could have told me when. Note I can only display 2 digits of the year. If I try using yyyy format I’ll get an ORA-01877. I think it’s interesting…
Using the algorithm discovered by David Bailey, Peter Borwein, and Simon Plouffe, you can easily generate values of pi with a simple recursive query… SQL> SELECT d, to_char(bbp, rpad(‘0.’,55, ‘9’)) bbp, 2 TO_CHAR( 3 SUM(bbp) OVER (ORDER BY d), 4 ‘9.’ || RPAD(‘9’, d – 1, ‘9’) 5 ) pi …
According to recent press release http://www.oracle.com/us/corporate/press/1563775 Yes- you can install 11gR2 on Oracle’s latest release of Linux. However, I was not successful in my attempts. Upon further research it seems the certification of db and os is only for 11.2.0.3 which is only available through download from Oracle support. That’s fine for work where we…
I don’t normally write a lot of java stored procedures. They simply aren’t necessary most of the time; but today somebody asked me a question that just seemed a perfect fit. They wanted to know how to generate a SHA-256 hash for a given string. For most hashing tasks I’d recommend Oracle’s built-in package DBMS_CRYPTO;…
I’ve known about Heterogeneous Services and Gateways for a while but only recently got around to playing with them. Like others, I chose the ODBC Gateway because the database license includes the ODBC usage, unlike the rest of the Gateways that are each licensed separately. First, create an ODBC DSN for whatever database and platform…
Welcome to my blog about Oracle database development. I’m also interested in math and frequently write pl/sql and sql snippets to solve various math problems. For example, here’s an article I wrote about solving a combinatorics problem found in dart games like 301,501,701, etc. Fun with Oracle SQL – Solving Checkouts in a Game of…