Reserved Words as Oracle Column Names

I saw a post on the web asking if one could create an Oracle table in which a column name was an Oracle reserved word like "TO" or "FROM". Now, not that I would do this, but it intrigued me, so I tried:

SQL> create table bogus (to varchar2(2));
create table bogus (to varchar2(2))
*
ERROR at line 1:
ORA-00904: : invalid identifier


SQL> CREATE TABLE bogus AS
2 SELECT dummy "TO", dummy "FROM" FROM DUAL;

Table created.

SQL> desc bogus
Name Null? Type
----- ----- --------------------------
TO VARCHAR2(1)
FROM VARCHAR2(1)

SQL> select * from bogus;

TO FROM
-- ----
X X

SQL>

I started up SQL Developer to see what the CREATE TABLE statement would be for the BOGUS table:

CREATE TABLE "BOGUS"
("TO" VARCHAR2(1),
"FROM" VARCHAR2(1));

To select from the BOGUS table:

SQL> select "TO", "FROM" from bogus;

TO FROM
-- ----
X X

SQL>

There it is.

APEX SQL Workshop Insufficient Privileges Error

An APEX user was attempting to create a table in the SQL Workshop and received the "ORA-01031 insufficient privileges" error message. I went into SQL Developer and was able to create the table. So why did it not work in APEX SQL Workshop?

After some "data dictionary" digging comparing this schema to one that works, I realized that the CREATE TABLE privilege was granted to the schema via a role and not a direct grant. Since APEX runs within PL/SQL you have to have the CREATE TABLE grant issued directly to the schema to be able to create a table in APEX. You cannot grant the privilege via a database role.

I just thought that I would post this in case someone else runs into this problem and so I will have the answer when the problem comes up again.

Oracle Reserved word as a Table name

I ran into a table today that was named GROUP, so I attempted to do a

SELECT * FROM GROUP;

Since GROUP is a reserved word in Oracle, I got an "ORA-00903: invalid table name" error. So how do I query the table? I went into SQL Developer and was able to view the data in the table via the "Data" tab. So how was that possible? It ended up SQL Developer was doing a

SELECT * FROM "GROUP";

I knew that SQL Developer placed double quotes around the schema, table, and column names in the CREATE TABLE statements in the "SQL" tab because those names could be mixed case. But the double quotes also allow those names to be reserved words as well.

NOTE: In my humble opinion naming tables or columns a reserved word is not a good thing to do.

ORDER BY Clause in "Filter" field In SQL Developer

I was in SQL Developer today and discovered something by accident. I double clicked on a table name in the "Connections" tab and went to the "Data" tab to view rows of data. In the "Filter:" field I entered a WHERE clause but accidentally also included an ORDER BY clause, too. The rows of data displayed in the order I requested. This got me to thinking. The "Sort" button provides a basic column by column sorting order, but if you need more complicated sorting logic you could just type it into the "Filter:" field.

This is useful if you want to edit a set of rows in a particular order. For example in our friend the EMP table, we could list all the rows where their salary is greater than 2000 listing the president first, analysts second, and all others third:

"When All Else Fails..."

This is on a shirt that I received as a present at work today.

Our "Friend" ORA-01555

Have you ever had your Oracle program ever get the dreaded ORA-01555: snapshot too old: rollback segment number 10 with name "_SYSSMU10$" too small error, you rerun the program, and it runs to completion with no errors? No changes to the code. No changes to the program parameters. No changes to the database. You just rerun the program and it works. As an application developer I would just say that the DBA needs to increase the amount of snapshot space and leave it up to the DBA to handle it. But since it is not a re-creatable event, the DBA could not do anything because we could not tell how much to increase the rollback space...

Well I ran into this sporadically at work recently and was able to overcome the problem. I overcame the problem with a programming change and not a database change. Basically the application when it was complete was deleting data out of a number of tables. We had some deletes inside of a cursor loop at the program's end.

FOR info IN cursor_x LOOP
DELETE FROM table1 WHERE ...
DELETE FROM table2 WHERE ...
...
END LOOP.

I finally determined that the problem was one iteration through the loop was deleting so much data that the database was cycling through the rollback space and when the cursor got to the top of the loop and attempted to get the next row of "info" the error would appear. So it was not the delete, but the "get" of the the row. The snap shot was too old. The database could not locate the next row of data in the cursor loop.

What was causing the sporadic nature of this problem was that we would have up to three of these programs running simultaneously. Some runs deleted small amounts of data and others deleted large amounts of data. If the programs were single threaded there was no problems. So the rollback space was large enough for one program to run, but multiple runs with at least one deleting a large amount of data would not work. In my option single threading the programs was not a fix. It was just a work around.

So since the data used for the cursor loop was not affected by the DELETEs inside the loop I did a BULK COLLECT and iterated through the array like:

OPEN cursor_x;
FETCH cursor_x INTO info;
CLOSE cursor_x;

FOR i IN 1 .. info.COUNT LOOP
DELETE FROM table1 WHERE ...
DELETE FROM table2 WHERE ...
...
END LOOP.

I figured I would share this in case you run into it. Usually I see the issue discussed from a DBA's perspective and not the programmer's perspective.

We have had no problems since. I had better not say that too loudly, the Oracle kernel may hear me;)

Diving into Java

Well I finally wrote my first professional Java program. It was professional in the sense that it did more than "Hello World" and was for work. There was data made available on an external Internet web page. To get the data the users had to: select from 4 drop down lists, press a button, copy the data out of MS Notepad, paste the data into Excel. The kicker was to get all the data they were going to have to do this process 3,591 times. My challenge was to automate the download of all this data off the web page directly into our Oracle database. This is the story of my two week "Dive into Java".

I first started looking at automated web page testing software to see if I could script the series of clicks. It became apparent quite quickly that I would be able to handle the clicks, but not the copy and paste of the data out of MS Notepad into Excel.

I then started looking at the external web page. I "inspected" the source code using Firebug to see all the values for the 4 drop down lists and got to thinking that if I could simulate these actions in Java maybe there would be a way of capturing the web page results to a text file that could be loaded into the database. So I started looking into Java. Keep in mind that I had read Mastering Java 2 5 years ago and only written HelloWorld.java. All of the people that got formal Java and J2EE training in our department have left the company, so I had "hack" my way through this.

I discussed the issue with a colleague of mine. He gave me a small snippet of Java code which connected to a web page and wrote the results to standard output. If I could take this code, loop through the permutations of the 4 drop down lists (arrays), and write the results out to a text file, I would have the data.

I first had to get into a Java IDE, Oracle JDeveloper. I was slightly familiar with it. I had used it for the Entity Relationship diagrammer. I had to get used to how projects mapped over to directories. That was not too bad.

My next challenge was that the Java program program was unable to get out through the our firewall at work. I could only run it at home where I had a direct connect to the Internet. Abstract class URLConnection (wow I sound like a Java developer) could not get through the firewall. I got to thinking, Java applications like JDeveloper connect out through the firewall by prompted for my firewall ID and password. So I did some searching on the Internet and found Authenticator.setDefault. With this I was able to get through the firewall out to the external web page, but I had to hard code an ID and password into the Java program. That had to change, so now I had to dig into "prompting" the user for the information.

So I did yet more Internet surfing (see a pattern here) and came up with DataExchangeTest.java from the Core Java 2 Fundamentals. I now was able to prompt for my firewall ID and password and got rid of all hard coding. (Trust me it is all gone.) This got me into Java Swing/AWT (more Java alphabet soup).

Now I could run the Java program from computer at work. The program created a text file on my computer which I had to FTP to my database server, SQL*Load the file into a database staging table, and run a data parsing database procedure to populate the final destination tables. Could I write the data into the staging table in the database, taking SQL*Load out of the picture, and "kick off" the data parsing procedure from Java? Here comes JDBC. More surfing gave me JDBC basics so I could "write" the data directly into the database and populate the destination table.

My next step is to run the Java as a regularly scheduled batch job. It could get the latest released data and publish what the differences are. This is not a user requirement yet. Maybe I will take that on in my "spare time".

Wow, what a two-week long struggle with no training, but I did it. I can now put Java on my resume, not yet.

Mike