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Diffstat (limited to 'src/man/explain.l')
| -rw-r--r-- | src/man/explain.l | 17 |
1 files changed, 9 insertions, 8 deletions
diff --git a/src/man/explain.l b/src/man/explain.l index 9bc0925bf2d..04c87da9ee7 100644 --- a/src/man/explain.l +++ b/src/man/explain.l @@ -1,6 +1,6 @@ .\" This is -*-nroff-*- .\" XXX standard disclaimer belongs here.... -.\" $Header: /cvsroot/pgsql/src/man/Attic/explain.l,v 1.10 1998/08/04 15:00:28 momjian Exp $ +.\" $Header: /cvsroot/pgsql/src/man/Attic/explain.l,v 1.11 1999/04/23 21:23:49 momjian Exp $ .TH EXPLAIN SQL 06/12/97 PostgreSQL PostgreSQL .SH NAME explain - explains statement execution details @@ -10,21 +10,22 @@ explain - explains statement execution details .fi .SH DESCRIPTION This command outputs details about the supplied query. The default -output is the computed query cost. \f2verbose\f1 displays the full query -plan and cost to your screen, and pretty-prints the plan to the postmaster -log file. +output is the computed query cost. The cost value is only meaningful to +the optimizer in comparing various query plans. \f2verbose\f1 displays +the full query plan and cost to your screen, and pretty-prints the plan +to the postmaster log file. .SH EXAMPLES In the examples, the table has a single column of float4. \fBcost\fR is the cost of scanning a base/join relation, -\fBsize\fR is the expected number of tuples from a scan, +\fBrows\fR is the expected number of rows from a scan, \fBwidth\fR is the length of a tuple. .nf tgl=> explain select a from test\g NOTICE:QUERY PLAN: -Seq Scan on test (cost=0.00 size=0 width=4) +Seq Scan on test (cost=0.00 rows=0 width=4) EXPLAIN tgl=> explain verbose select sum(a) from test; @@ -41,8 +42,8 @@ NOTICE:QUERY PLAN: :expr {VAR :varno 1 :varattno 1 :vartype 700 :varnoold 1 :varoattno 1}}) :qpqual <> :lefttree <> :righttree <> :scanrelid 1} :righttree <> :numagg 1 } -Aggregate (cost=0.00 size=0 width=0) - -> Seq Scan on test (cost=0.00 size=0 width=4) +Aggregate (cost=0.00 rows=0 width=0) + -> Seq Scan on test (cost=0.00 rows=0 width=4) .fi The Postgres optimizer has chosen to use a sequential scan to retrieve rows from |