Like (Apache Derby V10.14 Internals)

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

Fields
Modifier and Type Field Description

private static char anyChar

private static char anyString

private static java.lang.String SUPER_STRING

Fields
Modifier and Type	Field	Description
`private static char`	`anyChar`
`private static char`	`anyString`
`private static java.lang.String`	`SUPER_STRING`

Constructor Summary

Constructors
Modifier Constructor Description

private Like()

Constructors
Modifier	Constructor	Description
`private`	`Like()`

Method Summary

All Methods Static Methods Concrete Methods
Modifier and Type	Method	Description
`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

Class Like

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

anyChar

anyString

SUPER_STRING

Constructor Detail

Like

Method Detail

like

like

checkEquality

getMinLen

checkLengths

like

isOptimizable

greaterEqualStringFromParameter

greaterEqualStringFromParameterWithEsc

greaterEqualString

greaterEqualString

stripEscapesNoPatternChars

lessThanStringFromParameter

lessThanStringFromParameterWithEsc

lessThanString

isLikeComparisonNeeded

padWithNulls