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Version: 3.0

EXPLAIN

Description

Shows the logical or physical execution plans for a query statement.

Syntax

EXPLAIN <query>

Parameters

ParameterDescription
queryThe query statement whose execution plan you want to view.

Return value

Returns the execution plan of the input query statement.

ReturnDescription
avgRowSizeThe average size of the scanned data rows.
cardinalityThe total number of data rows in the scanned table.
colocateWhether the table is in colocate mode.
numNodesThe number of nodes to scan.
rollupThe Rollup materialized view that is used.
preaggregationThe status of preaggregation.
predicatesPredicates in the query.

Examples

mysql> EXPLAIN select count(*)
from store_sales,
household_demographics,
time_dim,
store
where ss_sold_time_sk = time_dim.t_time_sk
and ss_hdemo_sk = household_demographics.hd_demo_sk
and ss_store_sk = s_store_sk
and time_dim.t_hour = 8
and time_dim.t_minute >= 30
and household_demographics.hd_dep_count = 5
and store.s_store_name = 'ese'
order by count(*) limit 100;

+------------------------------------------------------------------------------+
| Explain String |
+------------------------------------------------------------------------------+
| PLAN FRAGMENT 0 |
| OUTPUT EXPRS:<slot 11> |
| PARTITION: UNPARTITIONED |
| RESULT SINK |
| 12:MERGING-EXCHANGE |
| limit: 100 |
| tuple ids: 5 |
| |
| PLAN FRAGMENT 1 |
| OUTPUT EXPRS: |
| PARTITION: RANDOM |
| STREAM DATA SINK |
| EXCHANGE ID: 12 |
| UNPARTITIONED |
| |
| 8:TOP-N |
| | order by: <slot 11> ASC |
| | offset: 0 |
| | limit: 100 |
| | tuple ids: 5 |
| | |
| 7:AGGREGATE (update finalize) |
| | output: count(*) |
| | group by: |
| | tuple ids: 4 |
| | |
| 6:HASH JOIN |
| | join op: INNER JOIN (BROADCAST) |
| | hash predicates: |
| | colocate: false, reason: left hash join node can not do colocate |
| | equal join conjunct: `ss_store_sk` = `s_store_sk` |
| | tuple ids: 0 2 1 3 |
| | |
| |----11:EXCHANGE |
| | tuple ids: 3 |
| | |
| 4:HASH JOIN |
| | join op: INNER JOIN (BROADCAST) |
| | hash predicates: |
| | colocate: false, reason: left hash join node can not do colocate |
| | equal join conjunct: `ss_hdemo_sk`=`household_demographics`.`hd_demo_sk`|
| | tuple ids: 0 2 1 |
| | |
| |----10:EXCHANGE |
| | tuple ids: 1 |
| | |
| 2:HASH JOIN |
| | join op: INNER JOIN (BROADCAST) |
| | hash predicates: |
| | colocate: false, reason: table not in same group |
| | equal join conjunct: `ss_sold_time_sk` = `time_dim`.`t_time_sk` |
| | tuple ids: 0 2 |
| | |
| |----9:EXCHANGE |
| | tuple ids: 2 |
| | |
| 0:OlapScanNode |
| TABLE: store_sales |
| PREAGGREGATION: OFF. Reason: `ss_sold_time_sk` is value column |
| partitions=1/1 |
| rollup: store_sales |
| tabletRatio=0/0 |
| tabletList= |
| cardinality=-1 |
| avgRowSize=0.0 |
| numNodes=0 |
| tuple ids: 0 |
| |
| PLAN FRAGMENT 2 |
| OUTPUT EXPRS: |
| PARTITION: RANDOM |
| |
| STREAM DATA SINK |
| EXCHANGE ID: 11 |
| UNPARTITIONED |
| |
| 5:OlapScanNode |
| TABLE: store |
| PREAGGREGATION: OFF. Reason: null |
| PREDICATES: `store`.`s_store_name` = 'ese' |
| partitions=1/1 |
| rollup: store |
| tabletRatio=0/0 |
| tabletList= |
| cardinality=-1 |
| avgRowSize=0.0 |
| numNodes=0 |
| tuple ids: 3 |
| |
| PLAN FRAGMENT 3 |
| OUTPUT EXPRS: |
| PARTITION: RANDOM |
| STREAM DATA SINK |
| EXCHANGE ID: 10 |
| UNPARTITIONED |
| |
| 3:OlapScanNode |
| TABLE: household_demographics |
| PREAGGREGATION: OFF. Reason: null |
| PREDICATES: `household_demographics`.`hd_dep_count` = 5 |
| partitions=1/1 |
| rollup: household_demographics |
| tabletRatio=0/0 |
| tabletList= |
| cardinality=-1 |
| avgRowSize=0.0 |
| numNodes=0 |
| tuple ids: 1 |
| |
| PLAN FRAGMENT 4 |
| OUTPUT EXPRS: |
| PARTITION: RANDOM |
| STREAM DATA SINK |
| EXCHANGE ID: 09 |
| UNPARTITIONED |
| |
| 1:OlapScanNode |
| TABLE: time_dim |
| PREAGGREGATION: OFF. Reason: null |
| PREDICATES: `time_dim`.`t_hour` = 8, `time_dim`.`t_minute` >= 30 |
| partitions=1/1 |
| rollup: time_dim |
| tabletRatio=0/0 |
| tabletList= |
| cardinality=-1 |
| avgRowSize=0.0 |
| numNodes=0 |
| tuple ids: 2 |
+------------------------------------------------------------------------------+
128 rows in set (0.02 sec)