Hi David, On Sun, Sep 5, 2021 at 8:32 PM David G. Johnston <david.g.johns...@gmail.com> wrote:
> On Sunday, September 5, 2021, Richard Michael <rmich...@edgeofthenet.org> > wrote: > >> >> Based on the documentation, I expected the first planned query text to >> be: `SELECT 10 AS data`, since it should be a custom plan with >> substituted values. However, the query text always contains a parameter >> symbol: `SELECT $1 AS data`. >> >> > A query plan is not the same as the query text. While the executed plan > can be generic or custom the query text is constant. > Thanks for drawing my attention to the difference between the query text and query plan. > If you want to see the difference between a generic and a custom plan you > need to comprise a query that would actually have different custom and > generic plans. Queries that don’t involve tables, indexes, or joins don’t > have any choices to make with respect to how they are executed. > After reading Laurenz's reply, I experimented again with `PREPARE basic(int) AS SELECT $1 AS number;" and the query plan logged in the log file (by auto_explain) does indeed show "Output: $1" on the sixth EXPLAIN EXECUTE! Sorry I missed this earlier. (The EXPLAIN EXECUTE output itself does not contain an "Output:" line, so I didn't notice this lack of parameter substitution in psql.) I appreciate your point about query plans which may not involve choices; thank you for mentioning it. Regards, Richard > David J. > >
