EXPLAIN
説明
クエリ文の論理または物理的な実行計画を表示します。
構文
EXPLAIN <query>
パラメータ
| パラメータ | 説明 |
|---|---|
| query | 実行計画を表示したいクエリ文です。 |
戻り値
入力されたクエリ文の実行計画を返します。
| 戻り値 | 説明 |
|---|---|
| avgRowSize | スキャンされたデータ行の平均サイズ。 |
| cardinality | スキャンされたテーブル内のデータ行の総数。 |
| colocate | テーブルがコロケートモードかどうか。 |
| numNodes | スキャンするノードの数。 |
| rollup | 使用される Rollup マテリアライズドビュー。 |
| preaggregation | 事前集計のステータス。 |
| predicates | クエリ内の述語。 |
例
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)