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Re: Extended Statistics set/restore/clear functions. - Mailing list pgsql-hackers

From Corey Huinker
Subject Re: Extended Statistics set/restore/clear functions.
Date
Msg-id CADkLM=d_mmTn3+ChL-z_ZomwOKT-BssQU+=6_a8WDv6A4b7uAA@mail.gmail.com
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In response to Re: Extended Statistics set/restore/clear functions.  (jian he <jian.universality@gmail.com>)
Responses Re: Extended Statistics set/restore/clear functions.
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extenssted statistics surely won't work on system columns,
how should we deal with case like:
```
{"attributes": [6, -1], "ndistinct": 14}
{"attributes": [6, -7], "ndistinct": 14},
```
issue a warning or error out saying that your attribute number is invalid?
Should we discourage using system columns as examples in comments here?

Negative numbers represent the Nth expression defined in the extended statistics object. So if you have extended statistics on a, b, length(a), length(b) then you can legally have -1 and -2 in the attributes, but nothing lower than that.
See functions pg_ndistinct_validate_items() and pg_depdendencies_validate_deps() as these check the attributes in the value against the definition of the extended stats object.

Though this does bring up a small naming problem: Elements of a pg_dependencies are Dependency, abbreviated to dep, but are also called Items like the elements in a pg_ndistinct. We should pick a standard name for such things (probably item) and use it everywhere.
 

I have added more test code in src/test/regress/sql/pg_ndistinct.sql,
to improve the code coverage.

I'm trying to implement those test cases, but I may have missed some.
 


this (and many other places) looks wrong, because
ereturn would really return ``(Datum) 0``, and this function returns
JsonParseErrorType.
so we have to errsave here.

Good point. Implemented.

 

NDistinctParseState.ndistinct should be integer,
otherwise pg_ndistinct_out will not be consistent with  pg_ndistinct_in?

+1  

Implemented many, but not all of these suggestions.



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