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https://issues.apache.org/jira/browse/DERBY-1623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12487668
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Manish Khettry commented on DERBY-1623:
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I have spent several days but I cannot seem to express the grammar for trim
without warnings from JavaCC. The warning says:
[java] Warning: Choice conflict involving two expansions at
[java] line 6268, column 5 and line 6279, column 5 respectively.
[java] A common prefix is: "leading" "+"
[java] Consider using a lookahead of 3 or more for earlier
expansion
I've included a skeleton of the production rules that I'm using. I'm also not
sure if additiveExpression is the right production to use in this case.
ValueNode
ansiTrimProduction() throws StandardException :
{
}
{
<LEADING> additiveExpression(null, 0, false)
{
return null; //TODO obviously return a ValueNode when warnings are
fixed.
}
|
LOOKAHEAD ( <LEADING> <FROM>)
<LEADING> <FROM> additiveExpression(null,0,false)
{
return null;
}
|
<LEADING> additiveExpression(null,0,false) <FROM>
additiveExpression(null,0,false)
{
return null;
}
}
>From reading the JavaCC documentation and this tutorial
>(https://javacc.dev.java.net/doc/lookahead.html) it seems the parser does not
>which production (the first or the third) to take when it reads a token like
>(+). Using a fixed lookahead to disambiguate between the two productions is
>not possible in this case. For now, I'm sort of stuck at this point. Any
>ponters would be appreciated.
> Add ANSI TRIM implementation
> ----------------------------
>
> Key: DERBY-1623
> URL: https://issues.apache.org/jira/browse/DERBY-1623
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Reporter: Emmanuel Bernard
> Assigned To: Manish Khettry
>
> JPA is requiring databases to support this ANSI feature esp the ability to
> chose the trimmed character
> TRIM([ [ LEADING | TRAILING | BOTH ] [ chars ] FROM ] str)
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