Github user dilipbiswal commented on a diff in the pull request:
https://github.com/apache/spark/pull/12460#discussion_r60335414
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/SparkSqlParser.scala ---
@@ -254,6 +251,21 @@ class SparkSqlAstBuilder extends AstBuilder {
}
}
+ /**
+ * A column path can be specified as an parameter to describe command.
It is a dot separated
+ * elements where the last element can be a String.
+ * TODO - check with Herman
--- End diff --
@hvanhovell Hi Herman, I tried very simple scenarios of using nested
columns and it seems to work ok. Let me paste the output here.
map
====
``` SQL
create table mp_t1 (a map <int, string>, b string) row format delimited
collection items terminated by '$' map keys terminated by '#';
load data local inpath '/data/mapfile' overwrite into table mp_t1;
select * from mp_t1;
a b
{100:"spark"} ABC
describe extended mp_t1.a.$key$;
Result
======
$key$ int from deserializer
```
Struct
====
``` SQL
create table ct_t (a struct<n1: string, n2: string>, b string) stored as
textfile;
insert into ct_t values (('abc', 'efg'), 'ABC');
spark-sql> select * from ct_t;
{"n1":"abb","n2":"efg"} ABC
spark-sql> describe extended ct_t.a.n1;
OK
n1 string from deserializer
```
Herman, based on hive syntax diagram, i was expecting the following
command to work.
describe extended mp_t1.a.'$key$';
However, i get a parse exception and when i remove the quotes it works like
following.
describe extended mp_t1.a.$key$
Given this, we can simply change the grammar to use a dot separated list of
identifiers, right ? Please
let me know what you think..
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