Github user paul-rogers commented on a diff in the pull request:
https://github.com/apache/drill/pull/907#discussion_r134034498
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/expr/fn/impl/RegexpUtil.java
---
@@ -76,12 +113,24 @@ public static String sqlToRegexLike(
/**
* Translates a SQL LIKE pattern to Java regex pattern.
*/
- public static String sqlToRegexLike(
+ public static sqlPatternInfo sqlToRegexLike(
String sqlPattern,
char escapeChar) {
int i;
final int len = sqlPattern.length();
final StringBuilder javaPattern = new StringBuilder(len + len);
+ final StringBuilder simplePattern = new StringBuilder(len);
+
+ // Figure out the pattern type and build simplePatternString
+ // as we are going through the sql pattern string
+ // to build java regex pattern string. This is better instead of using
+ // regex later for determining if a pattern is simple or not.
+ // Saves CPU cycles.
+ sqlPatternType patternType = sqlPatternType.NOT_SIMPLE;
+ boolean startsWith = false;
+ boolean endsWith = false;
+ boolean notSimple = false;
--- End diff --
Or, since your enum represents terminal states, create a new enum with
internal states. CONST_ONLY, WILDCARD, COMPLEX with transitions
```
initial: CONST_ONLY
all constant caracters, CONST_ONLY: -> CONST_ONLY
%, CONST_ONLY --> WILDCARD
any other special char, any state --> COMPLEX
%, WILDCARD --> COMPLEX
```
Or, even better, define a simple recursive decent parser in which states
are encoded as methods rather than as state variables.
```
parseConstant() ...
- parseWildcard()
- parseComplex()
parseWildcard() ...
- parseComplex()
parseComplex() ...
```
Here, I'm ignoring the details of detecting abc, abc%, ab%c, %abc. These
can also be represented as states with the resulting transitions.
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