pgsql: Avoid invoking PQfnumber in loop constructs

Avoid invoking PQfnumber in loop constructs

When looping over the resultset from a SQL query, extracting the field
number before the loop body to avoid repeated calls to PQfnumber is an
established pattern. On very wide tables this can have a performance
impact, but it wont be noticeable in the common case. This fixes a few
queries which were extracting the field number in the loop body.

Author: Hou Zhijie <houzj(dot)fnst(at)fujitsu(dot)com>
Reviewed-by: Nathan Bossart <bossartn(at)amazon(dot)com>
Discussion: https://postgr.es/m/OS0PR01MB57164C392783F29F6D0ECA0B94139@OS0PR01MB5716.jpnprd01.prod.outlook.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d782d5987e1022ba70171bcf3507cd87564ef23c

Modified Files
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src/bin/pg_dump/pg_dump.c | 94 +++++++++++++++++++++++++++++++++++------------
1 file changed, 71 insertions(+), 23 deletions(-)