Class PatternSearch

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

public final class PatternSearch extends 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 Details

    • PatternSearch

      public PatternSearch()
  • Method Details

    • testSearch

      public static boolean testSearch(String pattern, String expression, boolean result)
    • main

      public static void main(String[] args)
    • fullPatternMatch

      public static boolean fullPatternMatch(String pattern, 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(String pattern, 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.