mirror of https://github.com/apache/druid.git
* remove mentions of DruidQueryRel * Update docs/querying/sql-translation.md Co-authored-by: Victoria Lim <vtlim@users.noreply.github.com> * Update docs/querying/sql-translation.md Co-authored-by: Victoria Lim <vtlim@users.noreply.github.com> Co-authored-by: Victoria Lim <vtlim@users.noreply.github.com> Co-authored-by: Victoria Lim <vtlim@users.noreply.github.com>
This commit is contained in:
Vadim Ogievetsky
GitHub
parent
eba4bfeb66
commit
ff24901fda
|
|
@ -63,37 +63,139 @@ appreciated.
|
|||
## Interpreting EXPLAIN PLAN output
|
||||
|
||||
The [EXPLAIN PLAN](sql.md#explain-plan) functionality can help you understand how a given SQL query will
|
||||
be translated to native. For simple queries that do not involve subqueries or joins, the output of EXPLAIN PLAN
|
||||
is easy to interpret. The native query that will run is embedded as JSON inside a "DruidQueryRel" line:
|
||||
be translated to native.
|
||||
EXPLAIN PLAN statements return a `RESOURCES` column that describes the resource being queried as well as a `PLAN` column that contains a JSON array of native queries that Druid will run.
|
||||
For example, consider the following query:
|
||||
|
||||
```
|
||||
> EXPLAIN PLAN FOR SELECT COUNT(*) FROM wikipedia
|
||||
|
||||
DruidQueryRel(query=[{"queryType":"timeseries","dataSource":"wikipedia","intervals":"-146136543-09-08T08:23:32.096Z/146140482-04-24T15:36:27.903Z","granularity":"all","aggregations":[{"type":"count","name":"a0"}]}], signature=[{a0:LONG}])
|
||||
```sql
|
||||
EXPLAIN PLAN FOR
|
||||
SELECT
|
||||
channel,
|
||||
COUNT(*)
|
||||
FROM wikipedia
|
||||
WHERE channel IN (SELECT page FROM wikipedia GROUP BY page ORDER BY COUNT(*) DESC LIMIT 10)
|
||||
GROUP BY channel
|
||||
```
|
||||
|
||||
For more complex queries that do involve subqueries or joins, EXPLAIN PLAN is somewhat more difficult to interpret.
|
||||
For example, consider this query:
|
||||
The EXPLAIN PLAN statement returns the following plan:
|
||||
|
||||
```
|
||||
> EXPLAIN PLAN FOR
|
||||
> SELECT
|
||||
> channel,
|
||||
> COUNT(*)
|
||||
> FROM wikipedia
|
||||
> WHERE channel IN (SELECT page FROM wikipedia GROUP BY page ORDER BY COUNT(*) DESC LIMIT 10)
|
||||
> GROUP BY channel
|
||||
|
||||
DruidJoinQueryRel(condition=[=($1, $3)], joinType=[inner], query=[{"queryType":"groupBy","dataSource":{"type":"table","name":"__join__"},"intervals":{"type":"intervals","intervals":["-146136543-09-08T08:23:32.096Z/146140482-04-24T15:36:27.903Z"]},"granularity":"all","dimensions":["channel"],"aggregations":[{"type":"count","name":"a0"}]}], signature=[{d0:STRING, a0:LONG}])
|
||||
DruidQueryRel(query=[{"queryType":"scan","dataSource":{"type":"table","name":"wikipedia"},"intervals":{"type":"intervals","intervals":["-146136543-09-08T08:23:32.096Z/146140482-04-24T15:36:27.903Z"]},"resultFormat":"compactedList","columns":["__time","channel","page"],"granularity":"all"}], signature=[{__time:LONG, channel:STRING, page:STRING}])
|
||||
DruidQueryRel(query=[{"queryType":"topN","dataSource":{"type":"table","name":"wikipedia"},"dimension":"page","metric":{"type":"numeric","metric":"a0"},"threshold":10,"intervals":{"type":"intervals","intervals":["-146136543-09-08T08:23:32.096Z/146140482-04-24T15:36:27.903Z"]},"granularity":"all","aggregations":[{"type":"count","name":"a0"}]}], signature=[{d0:STRING}])
|
||||
```json
|
||||
[
|
||||
{
|
||||
"query": {
|
||||
"queryType": "topN",
|
||||
"dataSource": {
|
||||
"type": "join",
|
||||
"left": {
|
||||
"type": "table",
|
||||
"name": "wikipedia"
|
||||
},
|
||||
"right": {
|
||||
"type": "query",
|
||||
"query": {
|
||||
"queryType": "groupBy",
|
||||
"dataSource": {
|
||||
"type": "table",
|
||||
"name": "wikipedia"
|
||||
},
|
||||
"intervals": {
|
||||
"type": "intervals",
|
||||
"intervals": [
|
||||
"-146136543-09-08T08:23:32.096Z/146140482-04-24T15:36:27.903Z"
|
||||
]
|
||||
},
|
||||
"granularity": {
|
||||
"type": "all"
|
||||
},
|
||||
"dimensions": [
|
||||
{
|
||||
"type": "default",
|
||||
"dimension": "page",
|
||||
"outputName": "d0",
|
||||
"outputType": "STRING"
|
||||
}
|
||||
],
|
||||
"aggregations": [
|
||||
{
|
||||
"type": "count",
|
||||
"name": "a0"
|
||||
}
|
||||
],
|
||||
"limitSpec": {
|
||||
"type": "default",
|
||||
"columns": [
|
||||
{
|
||||
"dimension": "a0",
|
||||
"direction": "descending",
|
||||
"dimensionOrder": {
|
||||
"type": "numeric"
|
||||
}
|
||||
}
|
||||
],
|
||||
"limit": 10
|
||||
},
|
||||
"context": {
|
||||
"sqlOuterLimit": 101,
|
||||
"sqlQueryId": "ee616a36-c30c-4eae-af00-245127956e42",
|
||||
"useApproximateCountDistinct": false,
|
||||
"useApproximateTopN": false
|
||||
}
|
||||
}
|
||||
},
|
||||
"rightPrefix": "j0.",
|
||||
"condition": "(\"channel\" == \"j0.d0\")",
|
||||
"joinType": "INNER"
|
||||
},
|
||||
"dimension": {
|
||||
"type": "default",
|
||||
"dimension": "channel",
|
||||
"outputName": "d0",
|
||||
"outputType": "STRING"
|
||||
},
|
||||
"metric": {
|
||||
"type": "dimension",
|
||||
"ordering": {
|
||||
"type": "lexicographic"
|
||||
}
|
||||
},
|
||||
"threshold": 101,
|
||||
"intervals": {
|
||||
"type": "intervals",
|
||||
"intervals": [
|
||||
"-146136543-09-08T08:23:32.096Z/146140482-04-24T15:36:27.903Z"
|
||||
]
|
||||
},
|
||||
"granularity": {
|
||||
"type": "all"
|
||||
},
|
||||
"aggregations": [
|
||||
{
|
||||
"type": "count",
|
||||
"name": "a0"
|
||||
}
|
||||
],
|
||||
"context": {
|
||||
"sqlOuterLimit": 101,
|
||||
"sqlQueryId": "ee616a36-c30c-4eae-af00-245127956e42",
|
||||
"useApproximateCountDistinct": false,
|
||||
"useApproximateTopN": false
|
||||
}
|
||||
},
|
||||
"signature": [
|
||||
{
|
||||
"name": "d0",
|
||||
"type": "STRING"
|
||||
},
|
||||
{
|
||||
"name": "a0",
|
||||
"type": "LONG"
|
||||
}
|
||||
]
|
||||
}
|
||||
]
|
||||
```
|
||||
|
||||
Here, there is a join with two inputs. The way to read this is to consider each line of the EXPLAIN PLAN output as
|
||||
something that might become a query, or might just become a simple datasource. The `query` field they all have is
|
||||
called a "partial query" and represents what query would be run on the datasource represented by that line, if that
|
||||
line ran by itself. In some cases — like the "scan" query in the second line of this example — the query does not
|
||||
actually run, and it ends up being translated to a simple table datasource. See the [Join translation](#joins) section
|
||||
In this case the JOIN operator gets translated to a `join` datasource. See the [Join translation](#joins) section
|
||||
for more details about how this works.
|
||||
|
||||
We can see this for ourselves using Druid's [request logging](../configuration/index.md#request-logging) feature. After
|
||||
|
|
|
|||
Loading…
Reference in New Issue