com.mckoi.database
Class PatternSearch

java.lang.Object
  extended by com.mckoi.database.PatternSearch

public final class PatternSearch
extends java.lang.Object

This is a static class that performs the operations to do a pattern search on a given column of a table. The pattern syntax is very simple and follows that of the SQL standard.

It works as follows: The '%' character represents any sequence of characters. The '_' character represents some character.

Therefore, the pattern search 'Toby%' will find all rows that start with the string 'Toby' and end with any sequence of characters. The pattern 'T% Downer%' will find all names starting with T and containing 'Downer' somewhere in the end. The pattern '_at' will find all three letter words ending with 'at'.

NOTE: A 'ab%' type search is faster than a '%bc' type search. If the start of the search pattern is unknown then the entire contents of the column need to be accessed.

Author:
Tobias Downer

Constructor Summary
PatternSearch()
           
 
Method Summary
static boolean fullPatternMatch(java.lang.String pattern, java.lang.String str, char escape_char)
          Matches a pattern against a string and returns true if it matches or false otherwise.
static void main(java.lang.String[] args)
           
static boolean patternMatch(java.lang.String pattern, java.lang.String expression, char escape_char)
          This is the pattern match recurrsive method.
static boolean testSearch(java.lang.String pattern, java.lang.String expression, boolean result)
           
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

PatternSearch

public PatternSearch()
Method Detail

testSearch

public static boolean testSearch(java.lang.String pattern,
                                 java.lang.String expression,
                                 boolean result)

main

public static void main(java.lang.String[] args)

fullPatternMatch

public static boolean fullPatternMatch(java.lang.String pattern,
                                       java.lang.String str,
                                       char escape_char)
Matches a pattern against a string and returns true if it matches or false otherwise. This matches patterns that do not necessarily start with a wild card unlike the 'patternMatch' method.


patternMatch

public static boolean patternMatch(java.lang.String pattern,
                                   java.lang.String expression,
                                   char escape_char)
This is the pattern match recurrsive method. It recurses on each wildcard expression in the pattern which makes for slightly better efficiency than a character recurse algorithm. However, patterns such as "_%_a" will result in many recursive calls.

Returns true if the pattern matches.

NOTE: That "_%_" will be less efficient than "__%" and will produce the same result. NOTE: It requires that a wild card character is the first character in the expression. ISSUE: Pattern optimiser, we should optimise wild cards of type "%__" to "__%", or "%__%_%_%" to "____%". Optimised forms are identical in result and more efficient. This optimisation could be performed by the client during parsing of the LIKE statement. HACKING ISSUE: Badly formed wild cards may result in hogging of server side resources.