On 11/3/16, Jens Alfke <[email protected]> wrote:
> Does the query optimizer coalesce identical calls to deterministic
> functions? I’m thinking in particular of a statement like:
>
> CREATE INDEX byFoo ON jtable (json_extract(body, ‘$.foo’)) WHERE
> json_extract(body, ‘$.foo’) IS NOT NULL
>
> where it would improve performance if the JSON were not parsed twice.
In the case of the CREATE INDEX statement, no. On the other hand,
json_extract() is able to parse JSON at a rate of over 300MB/s so it
might not be as sluggish as you expect.
If you subsequently do something like:
SELECT * FROM jtable WHERE json_extract(body, '$.foo')=25;
Then the json_extract() function is not called at all. Not even once.
So under the theory that queries are more common than CREATE INDEX
statements, your total number of calls to json_extract seem like they
will be minimal.
--
D. Richard Hipp
[email protected]
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