soumyakanti3578 commented on code in PR #5721:
URL: https://github.com/apache/hive/pull/5721#discussion_r2034079502
##########
ql/src/test/queries/clientpositive/drop_stats_for_columns.q:
##########
@@ -0,0 +1,36 @@
+create table t1(i int, j int, k int);
+
+alter table t1 update statistics set('numRows'='10000', 'rawDataSize'='18000');
+alter table t1 update statistics for column i
set('numDVs'='2500','numNulls'='50','highValue'='1000','lowValue'='0');
Review Comment:
> How does this update works?
This is handled by
[AlterTableUpdateColumnStatistictAnalyzer](https://github.com/apache/hive/blob/b9ada6d8b30b325c91e6ab88a9deb7bb98b8a738/ql/src/java/org/apache/hadoop/hive/ql/ddl/table/misc/columnstats/AlterTableUpdateColumnStatistictAnalyzer.java).
Also checkout
[ColumnStatsUpdateTask](https://github.com/apache/hive/blob/b9ada6d8b30b325c91e6ab88a9deb7bb98b8a738/ql/src/java/org/apache/hadoop/hive/ql/exec/ColumnStatsUpdateTask.java),
where we construct column stats in `constructColumnStatsFromInput()` and then
build a `SetPartitionsStatsRequest` to persist the stats in HMS.
> alter table t1 update statistics for column i set();
This throws a `ParseException`:
```
org.apache.hadoop.hive.ql.parse.ParseException: line 2:50 cannot recognize
input near ')' '<EOF>' '<EOF>' in table properties list
```
`set()` cannot be empty as it expects `tableProperties`
([AlterClauseParser.g](https://github.com/apache/hive/blob/b9ada6d8b30b325c91e6ab88a9deb7bb98b8a738/parser/src/java/org/apache/hadoop/hive/ql/parse/AlterClauseParser.g#L258))
```
alterStatementSuffixUpdateStatsCol[boolean partition]
@init { gParent.pushMsg("update column statistics", state); }
@after { gParent.popMsg(state); }
: KW_UPDATE KW_STATISTICS KW_FOR KW_COLUMN? colName=identifier KW_SET
tableProperties (KW_COMMENT comment=StringLiteral)?
-> {partition}? ^(TOK_ALTERPARTITION_UPDATECOLSTATS $colName
tableProperties $comment?)
-> ^(TOK_ALTERTABLE_UPDATECOLSTATS $colName tableProperties
$comment?)
;
```
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