carlvinhust2012 commented on code in PR #16442:
URL: https://github.com/apache/doris/pull/16442#discussion_r1097321179
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fe/fe-core/src/main/java/org/apache/doris/analysis/SelectStmt.java:
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@@ -1291,11 +1291,54 @@ private void analyzeAggregation(Analyzer analyzer)
throws AnalysisException {
substituteOrdinalsAliases(groupingExprs, "GROUP BY", analyzer,
aliasFirst);
if (!groupByClause.isGroupByExtension() &&
!groupingExprs.isEmpty()) {
- ArrayList<Expr> tempExprs = new ArrayList<>(groupingExprs);
- groupingExprs.removeIf(Expr::isConstant);
- if (groupingExprs.isEmpty() && aggExprs.isEmpty()) {
- // should keep at least one expr to make the result correct
- groupingExprs.add(tempExprs.get(0));
+ /*
+ For performance reason, we want to remove constant column from
groupingExprs.
+ For example: `select 'abc', sum(a) from t group by 'abc'` is
equivalent to `select 1, sum(a) from t`
+ We can remove constant column `abc` from groupingExprs.
+ But there is an exception:
+ sql1: `select 'abc' from t group by 'abc'`
+ sql2: `select 'abc' from t`
+ sql1 is not equivalent to sql2.
+ We need to keep some constant column if all items in
groupingExprs are constant columns.
+ Consider sql3 `select a from (select "abc" as a, 'def' as b) T
group by b, a;`
+ if the column is in select list, this column should not be
removed.
+ */
+ if (aggExprs.isEmpty()) {
+ Expr theFirstConstantGroupingExpr = null;
+ boolean someGroupExprRemoved = false;
+ ArrayList<Expr> tempExprs = new ArrayList<>();
+ for (Expr groupExpr : groupingExprs) {
+ boolean keep = false;
+ if (groupExpr.isConstant()) {
+ if (theFirstConstantGroupingExpr == null) {
+ theFirstConstantGroupingExpr = groupExpr;
+ }
+ for (SelectListItem item : selectList.getItems()) {
+ if (item.getExpr() instanceof SlotRef) {
+ keep = ((SlotRef)
item.getExpr()).columnEqual(groupExpr);
+ if (keep) {
+ break;
+ }
+ }
+ }
+ }
+ if (keep) {
+ tempExprs.add(groupExpr);
+ } else {
+ someGroupExprRemoved = true;
+ }
+ }
+ if (someGroupExprRemoved) {
+ groupingExprs.clear();
+ groupingExprs.addAll(tempExprs);
+ //consider sql1, groupingExprs need at least one expr,
it can be
+ // any original grouping expr. we use the first one.
+ if (groupingExprs.isEmpty()) {
+ groupingExprs.add(theFirstConstantGroupingExpr);
+ }
+ }
+ } else {
+ groupingExprs.removeIf(Expr::isConstant);
Review Comment:
here， if ‘aggExprs.isEmpty()’ not true，no need add an expr to
'groupingExprs'?
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