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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>8.14. EXPLAIN — Presto 0.159 Documentation</title>
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<div class="header">
<h1 class="heading"><a href="../index.html">
<span>Presto 0.159 Documentation</span></a></h1>
<h2 class="heading"><span>8.14. EXPLAIN</span></h2>
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<div class="content">
<div class="section" id="explain">
<h1>8.14. EXPLAIN</h1>
<div class="section" id="synopsis">
<h2>Synopsis</h2>
<div class="highlight-none"><div class="highlight"><pre><span></span>EXPLAIN [ ( option [, ...] ) ] statement
where option can be one of:
FORMAT { TEXT | GRAPHVIZ }
TYPE { LOGICAL | DISTRIBUTED }
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Show the logical or distributed execution plan of a statement.</p>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<p>Logical plan:</p>
<div class="highlight-none"><div class="highlight"><pre><span></span>presto:tiny> EXPLAIN SELECT regionkey, count(*) FROM nation GROUP BY 1;
Query Plan
----------------------------------------------------------------------------------------------------------
- Output[regionkey, _col1] => [regionkey:bigint, count:bigint]
_col1 := count
- Exchange[GATHER] => regionkey:bigint, count:bigint
- Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint]
count := "count"("count_8")
- Exchange[REPARTITION] => regionkey:bigint, count_8:bigint
- Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint]
count_8 := "count"(*)
- TableScan[tpch:tpch:nation:sf0.01, original constraint=true] => [regionkey:bigint]
LAYOUT: tpch:nation:sf0.01
regionkey := tpch:regionkey
</pre></div>
</div>
<p>Distributed plan:</p>
<div class="highlight-none"><div class="highlight"><pre><span></span>presto:tiny> EXPLAIN (TYPE DISTRIBUTED) SELECT regionkey, count(*) FROM nation GROUP BY 1;
Query Plan
----------------------------------------------------------------------------------------------
Fragment 2 [SINGLE]
Output layout: [regionkey, count]
- Output[regionkey, _col1] => [regionkey:bigint, count:bigint]
_col1 := count
- RemoteSource[1] => [regionkey:bigint, count:bigint]
Fragment 1 [FIXED]
Output layout: [regionkey, count]
- Aggregate(FINAL)[regionkey] => [regionkey:bigint, count:bigint]
count := "count"("count_8")
- RemoteSource[0] => [regionkey:bigint, count_8:bigint]
Fragment 0 [SOURCE]
Output layout: [regionkey, count_8]
Output partitioning: [regionkey]
- Aggregate(PARTIAL)[regionkey] => [regionkey:bigint, count_8:bigint]
count_8 := "count"(*)
- TableScan[tpch:tpch:nation:sf0.01, original constraint=true] => [regionkey:bigint]
LAYOUT: tpch:nation:sf0.01
regionkey := tpch:regionkey
</pre></div>
</div>
</div>
<div class="section" id="see-also">
<h2>See Also</h2>
<p><a class="reference internal" href="explain-analyze.html"><span class="doc">EXPLAIN ANALYZE</span></a></p>
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