xuzifu666 commented on code in PR #5178:
URL: https://github.com/apache/calcite/pull/5178#discussion_r3784568447
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core/src/main/java/org/apache/calcite/adapter/enumerable/RexImpTable.java:
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@@ -2491,12 +2490,84 @@ protected FirstLastValueImplementor(SeekType seekType) {
AggResultContext result) {
WinAggResultContext winResult = (WinAggResultContext) result;
+ final boolean ignoreNulls =
+ info instanceof WinAggContext && ((WinAggContext)
info).ignoreNulls();
+ if (ignoreNulls) {
+ return implementResultIgnoreNulls(info, winResult);
+ }
+
return Expressions.condition(winResult.hasRows(),
winResult.rowTranslator(
winResult.computeIndex(Expressions.constant(0), seekType))
.translate(winResult.rexArguments().get(0), info.returnType()),
getDefaultValue(info.returnType()));
}
+
+ /**
+ * Implements FIRST_VALUE / LAST_VALUE with IGNORE NULLS by scanning the
+ * frame (forward for FIRST_VALUE, backward for LAST_VALUE) and returning
+ * the first non-null argument value, or the default value if all rows in
+ * the frame are null (or the frame is empty).
+ */
+ private Expression implementResultIgnoreNulls(AggContext info,
+ WinAggResultContext winResult) {
+ final Type returnType = info.returnType();
+ final RexNode arg = winResult.rexArguments().get(0);
+
+ // Use a boxed type internally so that a NULL comparison is always valid,
+ // even when the (frame-guaranteed non-empty) return type is a primitive.
+ // The surrounding window implementation converts the result back to the
+ // declared return type.
+ final Type boxType = Types.box(returnType);
+
+ final ParameterExpression res =
+ Expressions.parameter(0, boxType,
+ winResult.currentBlock().newName(
+ seekType == SeekType.START ? "first_value" : "last_value"));
+ winResult.currentBlock().add(Expressions.declare(0, res, NULL_EXPR));
+
+ final ParameterExpression idx =
+ Expressions.parameter(int.class,
+ winResult.currentBlock().newName("seekIdx"));
+
+ // Scan direction: FIRST_VALUE walks from start to end, LAST_VALUE walks
+ // from end back to start.
+ final boolean forward = seekType == SeekType.START;
+ final Expression from =
+ forward ? winResult.startIndex() : winResult.endIndex();
+ final Expression to =
+ forward ? winResult.endIndex() : winResult.startIndex();
+ final Expression condition =
+ forward
+ ? Expressions.lessThanOrEqual(idx, to)
+ : Expressions.greaterThanOrEqual(idx, to);
+ final Expression post =
+ forward
+ ? Expressions.postIncrementAssign(idx)
+ : Expressions.postDecrementAssign(idx);
+
+ final BlockBuilder loopBody = winResult.nestBlock();
Review Comment:
OK, I had added comments showing the generated code.
The method Javadoc now includes a full pseudo-code snippet of the generated
block (for FIRST_VALUE; LAST_VALUE scans backward), and I added inline comments
before the loop body and the if (hasRows) { for (...) } wrapper to show what
each statement generates.
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