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remove mentions of DruidQueryRel from docs (#13033)
* 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>
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Vadim Ogievetsky
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@ -63,37 +63,139 @@ appreciated.
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## Interpreting EXPLAIN PLAN output
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The [EXPLAIN PLAN](sql.md#explain-plan) functionality can help you understand how a given SQL query will
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be translated to native. For simple queries that do not involve subqueries or joins, the output of EXPLAIN PLAN
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is easy to interpret. The native query that will run is embedded as JSON inside a "DruidQueryRel" line:
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be translated to native.
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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.
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For example, consider the following query:
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```
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> EXPLAIN PLAN FOR SELECT COUNT(*) FROM wikipedia
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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}])
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```sql
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EXPLAIN PLAN FOR
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SELECT
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channel,
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COUNT(*)
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FROM wikipedia
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WHERE channel IN (SELECT page FROM wikipedia GROUP BY page ORDER BY COUNT(*) DESC LIMIT 10)
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GROUP BY channel
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```
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For more complex queries that do involve subqueries or joins, EXPLAIN PLAN is somewhat more difficult to interpret.
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For example, consider this query:
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The EXPLAIN PLAN statement returns the following plan:
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```
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> EXPLAIN PLAN FOR
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> SELECT
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> channel,
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> COUNT(*)
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> FROM wikipedia
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> WHERE channel IN (SELECT page FROM wikipedia GROUP BY page ORDER BY COUNT(*) DESC LIMIT 10)
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> GROUP BY channel
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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}])
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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}])
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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}])
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```json
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[
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{
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"query": {
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"queryType": "topN",
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"dataSource": {
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"type": "join",
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"left": {
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"type": "table",
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"name": "wikipedia"
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},
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"right": {
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"type": "query",
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"query": {
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"queryType": "groupBy",
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"dataSource": {
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"type": "table",
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"name": "wikipedia"
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},
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"intervals": {
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"type": "intervals",
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"intervals": [
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"-146136543-09-08T08:23:32.096Z/146140482-04-24T15:36:27.903Z"
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]
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},
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"granularity": {
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"type": "all"
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},
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"dimensions": [
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{
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"type": "default",
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"dimension": "page",
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"outputName": "d0",
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"outputType": "STRING"
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}
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],
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"aggregations": [
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{
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"type": "count",
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"name": "a0"
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}
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],
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"limitSpec": {
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"type": "default",
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"columns": [
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{
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"dimension": "a0",
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"direction": "descending",
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"dimensionOrder": {
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"type": "numeric"
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}
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}
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],
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"limit": 10
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},
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"context": {
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"sqlOuterLimit": 101,
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"sqlQueryId": "ee616a36-c30c-4eae-af00-245127956e42",
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"useApproximateCountDistinct": false,
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"useApproximateTopN": false
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}
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}
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},
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"rightPrefix": "j0.",
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"condition": "(\"channel\" == \"j0.d0\")",
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"joinType": "INNER"
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},
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"dimension": {
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"type": "default",
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"dimension": "channel",
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"outputName": "d0",
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"outputType": "STRING"
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},
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"metric": {
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"type": "dimension",
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"ordering": {
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"type": "lexicographic"
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}
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},
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"threshold": 101,
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"intervals": {
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"type": "intervals",
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"intervals": [
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"-146136543-09-08T08:23:32.096Z/146140482-04-24T15:36:27.903Z"
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]
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},
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"granularity": {
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"type": "all"
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},
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"aggregations": [
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{
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"type": "count",
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"name": "a0"
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}
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],
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"context": {
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"sqlOuterLimit": 101,
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"sqlQueryId": "ee616a36-c30c-4eae-af00-245127956e42",
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"useApproximateCountDistinct": false,
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"useApproximateTopN": false
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}
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},
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"signature": [
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{
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"name": "d0",
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"type": "STRING"
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},
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{
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"name": "a0",
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"type": "LONG"
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}
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]
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}
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]
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```
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Here, there is a join with two inputs. The way to read this is to consider each line of the EXPLAIN PLAN output as
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something that might become a query, or might just become a simple datasource. The `query` field they all have is
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called a "partial query" and represents what query would be run on the datasource represented by that line, if that
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line ran by itself. In some cases — like the "scan" query in the second line of this example — the query does not
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actually run, and it ends up being translated to a simple table datasource. See the [Join translation](#joins) section
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In this case the JOIN operator gets translated to a `join` datasource. See the [Join translation](#joins) section
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for more details about how this works.
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We can see this for ourselves using Druid's [request logging](../configuration/index.md#request-logging) feature. After
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