Class Like

java.lang.Object
org.apache.derby.iapi.types.Like

public class Like extends Object
Like matching algorithm. Not too speedy for %s. SQL92 says the escape character can only and must be followed by itself, %, or _. So if you choose % or _ as the escape character, you can no longer do that sort of matching. Not the most recent Like -- missing the unit tests
  • Field Details

  • Constructor Details

    • Like

      private Like()
  • Method Details

    • like

      public static Boolean like(char[] val, int valLength, char[] pat, int patLength, char[] escape, int escapeLength, RuleBasedCollator collator) throws StandardException
      This method gets called for UCS_BASIC and territory based character string types to look for a pattern in a value string. It also deals with escape character if user has provided one.
      Parameters:
      val - value to compare. if null, result is null.
      valLength - length of val
      pat - pattern to compare. if null, result is null.
      patLength - length of pat
      escape - escape character. Must be 1 char long. if null, no escape character is used.
      escapeLength - length of escape
      collator - null if we are dealing with UCS_BASIC character string types. If not null, then we use it to get collation elements for characters in val and non-metacharacters in pat to do the comparison.
      Returns:
      null if val or pat null, otherwise true if match and false if not.
      Throws:
      StandardException - thrown if data invalid
    • like

      private static Boolean like(char[] val, int vLoc, int vEnd, char[] pat, int pLoc, int pEnd, char[] escape, int escapeLength, RuleBasedCollator collator) throws StandardException
      Throws:
      StandardException
    • checkEquality

      private static boolean checkEquality(char[] val, int vLoc, char[] pat, int pLoc, RuleBasedCollator collator)
      If the character in val matches the character in pat, then it does not matter if the database is UCS_BASIC or territory based, we simply return TRUE from the method. If the characters do not match and we are running with UCS_BASIC collation, then we will return FALSE. But if the database is territory based, then we want to use the Collator for the territory to determine if the Collator treats the 2 characters as equal (ie if their collation elements match, then the 2 characters are equal even if they are not the same character).
      Parameters:
      val - value to compare.
      vLoc - character position in val.
      pat - pattern to look for in val.
      pLoc - character position in pat.
      collator - null if we are dealing with UCS_BASIC character string types. If not null, then we use it to determine the equality of the 2 characters in pat and val if they are not same.
      Returns:
      TRUE if the character in val and vLoc match based on straight equality or collation element based equality. Otherwise we will return FALSE.
    • getMinLen

      static int getMinLen(char[] pattern, int pStart, int pEnd, boolean haveEsc, char escChar)
      Calculate the shortest length string that could match this pattern
    • checkLengths

      static Boolean checkLengths(int vLoc, int vEnd, int pLoc, char[] pat, int pEnd)
      checkLengths Returns null if we are not done. Returns true if we are at the end of our value and pattern Returns false if there is more pattern left but out of input value
      Parameters:
      vLoc - current index into char[] val
      vEnd - end index or our value
      pLoc - current index into our char[] pattern
      pat - pattern char []
      pEnd - end index of our pattern []
    • like

      public static Boolean like(char[] value, int valueLength, char[] pattern, int patternLength, RuleBasedCollator collator) throws StandardException
      Throws:
      StandardException
    • isOptimizable

      public static boolean isOptimizable(String pattern)
      Determine whether or not this LIKE can be transformed into optimizable clauses. It can if the pattern is non-null and if the length == 0 or the first character is not a wild card.
      Parameters:
      pattern - The right side of the LIKE
      Returns:
      Whether or not the LIKE can be transformed
    • greaterEqualStringFromParameter

      public static String greaterEqualStringFromParameter(String pattern, int maxWidth) throws StandardException
      Throws:
      StandardException
    • greaterEqualStringFromParameterWithEsc

      public static String greaterEqualStringFromParameterWithEsc(String pattern, String escape, int maxWidth) throws StandardException
      Throws:
      StandardException
    • greaterEqualString

      public static String greaterEqualString(String pattern, String escape, int maxWidth) throws StandardException
      Return the substring from the pattern for the optimization >= clause.
      Parameters:
      pattern - The right side of the LIKE
      escape - The escape clause
      maxWidth - Maximum length of column, for null padding
      Returns:
      The String for the >= clause
      Throws:
      StandardException
    • greaterEqualString

      private static String greaterEqualString(String pattern, char escChar) throws StandardException
      greaterEqualString -- for Escape clause only Walk the pattern character by character
      Parameters:
      pattern - like pattern to build from
      escChar - the escape character in the pattern
      Throws:
      StandardException
    • stripEscapesNoPatternChars

      public static String stripEscapesNoPatternChars(String pattern, char escChar) throws StandardException
      stripEscapesNoPatternChars
      Parameters:
      pattern - pattern String to search
      escChar - the escape character
      Returns:
      a stripped of ESC char string if no pattern chars, null otherwise
      Throws:
      StandardException - thrown if data invalid
    • lessThanStringFromParameter

      public static String lessThanStringFromParameter(String pattern, int maxWidth) throws StandardException
      Throws:
      StandardException
    • lessThanStringFromParameterWithEsc

      public static String lessThanStringFromParameterWithEsc(String pattern, String escape, int maxWidth) throws StandardException
      Throws:
      StandardException
    • lessThanString

      public static String lessThanString(String pattern, String escape, int maxWidth) throws StandardException
      Return the substring from the pattern for the < clause.
      Parameters:
      pattern - The right side of the LIKE
      escape - The escape clause
      maxWidth - Maximum length of column, for null padding
      Returns:
      The String for the < clause
      Throws:
      StandardException - thrown if data invalid
    • isLikeComparisonNeeded

      public static boolean isLikeComparisonNeeded(String pattern)
      Return whether or not the like comparison is still needed after performing the like transformation on a constant string. The comparison is not needed if the constant string is of the form: CONSTANT% (constant followed by a trailing %)
      Parameters:
      pattern - The right side of the LIKE
      Returns:
      Whether or not the like comparison is still needed.
    • padWithNulls

      private static String padWithNulls(String string, int len)
      Pad a string with null characters, in order to make it > and < comparable with SQLChar.
      Parameters:
      string - The string to pad
      len - Max number of characters to pad to
      Returns:
      the string padded with 0s up to the given length