EXPLAIN
說明
EXPLAIN 陳述式用於提供輸入陳述式的邏輯/實體計畫。預設情況下，此子句僅提供有關實體計畫的資訊。
語法
EXPLAIN [ EXTENDED | CODEGEN | COST | FORMATTED ] statement
參數
-
EXTENDED
產生已剖析的邏輯計畫、已分析的邏輯計畫、已最佳化的邏輯計畫和實體計畫。已剖析的邏輯計畫是從查詢中萃取的未解析計畫。已分析的邏輯計畫會轉換，將 unresolvedAttribute 和 unresolvedRelation 轉換成完全型別的物件。已最佳化的邏輯計畫會透過一組最佳化規則轉換，產生實體計畫。
-
CODEGEN
產生陳述式的程式碼 (如果有) 和實體計畫。
-
COST
如果計畫節點統計資料可用，則會產生邏輯計畫和統計資料。
-
FORMATTED
產生兩個區段：實體計畫大綱和節點詳細資料。
-
statement
指定要說明的 SQL 陳述式。
範例
-- Default Output
EXPLAIN select k, sum(v) from values (1, 2), (1, 3) t(k, v) group by k;
+----------------------------------------------------+
| plan|
+----------------------------------------------------+
| == Physical Plan ==
*(2) HashAggregate(keys=[k#33], functions=[sum(cast(v#34 as bigint))])
+- Exchange hashpartitioning(k#33, 200), true, [id=#59]
+- *(1) HashAggregate(keys=[k#33], functions=[partial_sum(cast(v#34 as bigint))])
+- *(1) LocalTableScan [k#33, v#34]
|
+----------------------------------------------------
-- Using Extended
EXPLAIN EXTENDED select k, sum(v) from values (1, 2), (1, 3) t(k, v) group by k;
+----------------------------------------------------+
| plan|
+----------------------------------------------------+
| == Parsed Logical Plan ==
'Aggregate ['k], ['k, unresolvedalias('sum('v), None)]
+- 'SubqueryAlias `t`
+- 'UnresolvedInlineTable [k, v], [List(1, 2), List(1, 3)]
== Analyzed Logical Plan ==
k: int, sum(v): bigint
Aggregate [k#47], [k#47, sum(cast(v#48 as bigint)) AS sum(v)#50L]
+- SubqueryAlias `t`
+- LocalRelation [k#47, v#48]
== Optimized Logical Plan ==
Aggregate [k#47], [k#47, sum(cast(v#48 as bigint)) AS sum(v)#50L]
+- LocalRelation [k#47, v#48]
== Physical Plan ==
*(2) HashAggregate(keys=[k#47], functions=[sum(cast(v#48 as bigint))], output=[k#47, sum(v)#50L])
+- Exchange hashpartitioning(k#47, 200), true, [id=#79]
+- *(1) HashAggregate(keys=[k#47], functions=[partial_sum(cast(v#48 as bigint))], output=[k#47, sum#52L])
+- *(1) LocalTableScan [k#47, v#48]
|
+----------------------------------------------------+
-- Using Formatted
EXPLAIN FORMATTED select k, sum(v) from values (1, 2), (1, 3) t(k, v) group by k;
+----------------------------------------------------+
| plan|
+----------------------------------------------------+
| == Physical Plan ==
* HashAggregate (4)
+- Exchange (3)
+- * HashAggregate (2)
+- * LocalTableScan (1)
(1) LocalTableScan [codegen id : 1]
Output: [k#19, v#20]
(2) HashAggregate [codegen id : 1]
Input: [k#19, v#20]
(3) Exchange
Input: [k#19, sum#24L]
(4) HashAggregate [codegen id : 2]
Input: [k#19, sum#24L]
|
+----------------------------------------------------+