Sunday, June 17, 2007

Char_Instr - Another Matching Algorithm

I've using Soundex, Double Metaphone, Levenshtein Distance and other string matching algorithms, but somethings it is the simple things that work best.

Here is a function I wrote in PL/SQL utilizing the INSTR() function to traverse through one string, checking each character as to whether or not it exists in the another string.

This has been useful in checking for duplicates in mailing lists as well as identifying potential duplicates that should be reviewed. The function returns the number of characters from the second string that are the same as the first string.

I've found the use of the Soundex to be too loose and the Levenshtein Distance algorithm to be lacking in its handling of transposed characters. Use of this function will give you a count of how many chars are the same regardless of position in the string.

Function: char_instr (str1, str2)

Purpose: To check how many characters from one string

exist in another string. The return value is the number
of characters that exist in the in both strings.

FUNCTION char_instr
v_exists NUMBER := 0;
v_occurs NUMBER := 0;
v_length NUMBER;
Get the length of the str2
v_length := LENGTH(str2);
Loop through str2 and check if char exists in str1
IF( v_length > 0 ) THEN
FOR x IN 1..v_length LOOP
v_exists := INSTR(UPPER(str1), SUBSTR(UPPER(str2), x, 1));
IF(v_exists>0) THEN
v_occurs := v_occurs + 1;
RETURN v_occurs;
END char_instr;

Thursday, June 14, 2007

SQL Cheat Sheet

I've put together this page to give quick links to all the Oracle SQL tricks that I find myself continuing to search for on the net. This is a quick reference guide and will be expanded regularly.

Oracle SQL Cheat Sheet

SQL Introduction and Definitions


Create a Delimited Output in SQL Plus

How to Rename a Column in Oracle SQL

How to Delete a Column from a Table

Use of Variables in SQL Plus or PL/SQL

Format Query Results to Display Currency

Display Seconds Past Midnight

Select Only Top Results in a Query

Use of Wildcards in Oracle SQL

What is NVL and how does it work?

How to Use Decode in Oracle SQL

How to Round Off a Number in Oracle SQL

Debug JDBC Connectivity with Oracle Thin Client

Oracle String Matching Algorithm - CHAR_INSTR

If you have any other tips or suggested entries, let me know!

Saturday, June 02, 2007

Nice Bike Tom!

Check out these shots of Tom Cruise's new bike. I hear it has a Ducati engine and was custom built for him, sized to fit.