Tom Lane wrote:
>
> According to the SQL spec it's "implementation defined", which means
> different DBs could do it differently but they have to tell you what
> they will do. "Implementation dependent" effectively means "the
> behavior is not specified at all".
One problem is that even if the server is supposed to tell you, the means it
uses to do so can vary widely: paper manual, release notes, variable accessible
by SHOW, value accessible by a special query (like the old-style PostgreSQL
EXPLAIN output) value accessible by a standard query (provided you know the
syntax in advance)...
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
