Greetings, everyone.
Right now I am working on this JIRA:
IMPALA-889<http://issues.cloudera.org/browse/IMPALA-889>: Add support for
ISO-SQL trim()
In order to confirm the SQL standard like SELECT trim(where chars FROM source);
It is necessary to modify the /root/Impala/fe/src/main/cup/sql-parser.cup file.
The following code is added:
function_call_expr ::=
function_name:fn_name LPAREN RPAREN
{:
RESULT = FunctionCallExpr.createExpr(
fn_name, new FunctionParams(new ArrayList<Expr>()));
:}
| function_name:fn_name LPAREN function_params:params RPAREN
{: RESULT = FunctionCallExpr.createExpr(fn_name, params); :}
// Below is a special case for EXTRACT. Idents are used to avoid adding new
keywords.
| function_name:fn_name LPAREN IDENT:u KW_FROM expr:t RPAREN
{: RESULT = new ExtractFromExpr(fn_name, u, t); :}
// MY NEW CODE
| function_name:fn_name LPAREN STRING_LITERAL:w expr:c KW_FROM expr:s RPAREN
{: RESULT = new TrimExpr(fn_name, w, c, s); :}
;
And then I also implemented the corresponding TrimExpr.java file.
After that, I build the front end code like:
cd ${IMPALA_HOME}/fe && mvn clean package dependency:copy-dependencies
-DskipTests=true
In the Impala shell, I run the following query:
select trim("a" "xyz" from "abc")
And then I got this error:
ERROR: AnalysisException: Expression ''xyz'' in 'TRIM(a 'xyz' FROM 'abc')' has
a return type of STRING but a STRING is required.
This ERROR is thrown by a routine in the TrimExpr.java
@Override
protected String getFunctionNotFoundError(Type[] argTypes) {
Expr e = children_.get(2);
return "Expression '" + e.toSql() + "' in '" + toSql() + "' has a return
type of "
+ e.getType().toSql() + " but a STRING is required.";
}
It seems Impala can't find the back-end implementation for this front-end
expression
SELECT trim(where chars FROM source);
So here comes my question: how to associate the front-end expression coded in
the sql-parser.cup with back-end implementation? I know there exists some other
similar function named extract(IDENT from Timestamp) which is implemented in
the udf-builtins.h and I have done the same thing. But that does not work - so
I must miss something important.
Any hint or clue is highly appreciated. Thank you. :)
