org.apache.derby.iapi.types
Class Like

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

public class Like
extends java.lang.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 Summary

private static char	anyChar
private static char	anyString
private static java.lang.String	SUPER_STRING

Constructor Summary

private

Like()

Method Summary

private static boolean	checkEquality(char[] val, int vLoc, char[] pat, int pLoc, java.text.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.
(package private) static java.lang.Boolean	checkLengths(int vLoc, int vEnd, int pLoc, char[] pat, int pEnd) checkLengths Returns null if we are not done.
(package private) static int	getMinLen(char[] pattern, int pStart, int pEnd, boolean haveEsc, char escChar) Calculate the shortest length string that could match this pattern
private static java.lang.String	greaterEqualString(java.lang.String pattern, char escChar) greaterEqualString -- for Escape clause only Walk the pattern character by character
static java.lang.String	greaterEqualString(java.lang.String pattern, java.lang.String escape, int maxWidth) Return the substring from the pattern for the optimization >= clause.
static java.lang.String	greaterEqualStringFromParameter(java.lang.String pattern, int maxWidth)
static java.lang.String	greaterEqualStringFromParameterWithEsc(java.lang.String pattern, java.lang.String escape, int maxWidth)
static boolean	isLikeComparisonNeeded(java.lang.String pattern) Return whether or not the like comparison is still needed after performing the like transformation on a constant string.
static boolean	isOptimizable(java.lang.String pattern) Determine whether or not this LIKE can be transformed into optimizable clauses.
static java.lang.String	lessThanString(java.lang.String pattern, java.lang.String escape, int maxWidth) Return the substring from the pattern for the < clause.
static java.lang.String	lessThanStringFromParameter(java.lang.String pattern, int maxWidth)
static java.lang.String	lessThanStringFromParameterWithEsc(java.lang.String pattern, java.lang.String escape, int maxWidth)
static java.lang.Boolean	like(char[] val, int valLength, char[] pat, int patLength, char[] escape, int escapeLength, java.text.RuleBasedCollator collator) This method gets called for UCS_BASIC and territory based character string types to look for a pattern in a value string.
static java.lang.Boolean	like(char[] value, int valueLength, char[] pattern, int patternLength, java.text.RuleBasedCollator collator)
private static java.lang.Boolean	like(char[] val, int vLoc, int vEnd, char[] pat, int pLoc, int pEnd, char[] escape, int escapeLength, java.text.RuleBasedCollator collator)
private static java.lang.String	padWithNulls(java.lang.String string, int len) Pad a string with null characters, in order to make it > and < comparable with SQLChar.
static java.lang.String	stripEscapesNoPatternChars(java.lang.String pattern, char escChar) stripEscapesNoPatternChars

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

anyChar

private static final char anyChar

See Also:

Constant Field Values

anyString

private static final char anyString

See Also:

Constant Field Values

SUPER_STRING

private static final java.lang.String SUPER_STRING

See Also:

Constant Field Values

Constructor Detail

Like

private Like()

Method Detail

like

public static java.lang.Boolean like(char[] val,
                                     int valLength,
                                     char[] pat,
                                     int patLength,
                                     char[] escape,
                                     int escapeLength,
                                     java.text.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 java.lang.Boolean like(char[] val,
                                      int vLoc,
                                      int vEnd,
                                      char[] pat,
                                      int pLoc,
                                      int pEnd,
                                      char[] escape,
                                      int escapeLength,
                                      java.text.RuleBasedCollator collator)
                               throws StandardException

Throws:

StandardException

checkEquality

private static boolean checkEquality(char[] val,
                                     int vLoc,
                                     char[] pat,
                                     int pLoc,
                                     java.text.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 java.lang.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 java.lang.Boolean like(char[] value,
                                     int valueLength,
                                     char[] pattern,
                                     int patternLength,
                                     java.text.RuleBasedCollator collator)
                              throws StandardException

Throws:

StandardException

isOptimizable

public static boolean isOptimizable(java.lang.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 java.lang.String greaterEqualStringFromParameter(java.lang.String pattern,
                                                               int maxWidth)
                                                        throws StandardException

Throws:

StandardException

greaterEqualStringFromParameterWithEsc

public static java.lang.String greaterEqualStringFromParameterWithEsc(java.lang.String pattern,
                                                                      java.lang.String escape,
                                                                      int maxWidth)
                                                               throws StandardException

Throws:

StandardException

greaterEqualString

public static java.lang.String greaterEqualString(java.lang.String pattern,
                                                  java.lang.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 java.lang.String greaterEqualString(java.lang.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 java.lang.String stripEscapesNoPatternChars(java.lang.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 java.lang.String lessThanStringFromParameter(java.lang.String pattern,
                                                           int maxWidth)
                                                    throws StandardException

Throws:

StandardException

lessThanStringFromParameterWithEsc

public static java.lang.String lessThanStringFromParameterWithEsc(java.lang.String pattern,
                                                                  java.lang.String escape,
                                                                  int maxWidth)
                                                           throws StandardException

Throws:

StandardException

lessThanString

public static java.lang.String lessThanString(java.lang.String pattern,
                                              java.lang.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(java.lang.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 java.lang.String padWithNulls(java.lang.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