[BUGS] BUG #14715: Constraint exclusion isn't used in function usinglanguage sql

The following bug has been logged on the website:

Bug reference:      14715
Logged by:          Clive Evans
Email address:      cliveevans@ntlworld.com
PostgreSQL version: 9.6.3
Operating system:   CentOS Linux release 7.3.1611
Description:

The same query written using PL/PGSQL will only scan the expected partition
tables.

For example:
partition_test=# DO                                                                             
$$             
BEGIN                          
CREATE TABLE customer_reviews(   customer_id TEXT,   review_date DATE,   review_rating INTEGER,   review_votes INTEGER,
 review_helpful_votes INTEGER,   product_id CHAR(10),   product_title TEXT,
          product_sales_rank BIGINT,   product_group TEXT,   product_category TEXT,   product_subcategory TEXT,
similar_product_idsCHAR(10)[]
 
);                                
FOR n in 2000..2004
LOOP                                                     EXECUTE 'CREATE TABLE customer_reviews_' || n || ' (check
(review_date>= 
''' || n || '-01-01'' AND review_date < ''' || n + 1 || '-01-01'')) INHERITS
(customer_reviews) ;';
END LOOP;
END                             
$$ ;
DO
Time: 15.647 ms
partition_test=# CREATE OR REPLACE FUNCTION title_vs_review_sql(start_date
DATE, end_date DATE)
RETURNS TABLE (  title_length_bucket INTEGER,  review_average NUMERIC,  count BIGINT
) AS                 
$BODY$                    
SELECT                      width_bucket(length(product_title), 1, 50, 5) title_length_bucket,
round(avg(review_rating),2) AS review_average,   count(*)
 
FROM                            customer_reviews
WHERE                        product_group = 'Book'   AND                              review_date BETWEEN start_date
ANDend_date
 
GROUP BY   title_length_bucket
ORDER BY
                           
title_length_bucket        
$BODY$
LANGUAGE SQL;
CREATE FUNCTION
Time: 0.918 ms
partition_test=# CREATE OR REPLACE FUNCTION
title_vs_review_plpgsql(start_date DATE, end_date DATE)
RETURNS TABLE (  title_length_bucket INTEGER,  review_average NUMERIC,  count BIGINT
) AS
$BODY$
BEGIN
RETURN QUERY       SELECT           width_bucket(length(product_title), 1, 50, 5)
title_length_bucket,           round(avg(review_rating), 2) AS review_average,           count(*)       FROM
customer_reviews      WHERE           product_group = 'Book'           AND           review_date BETWEEN start_date AND
end_date      GROUP BY           title_length_bucket       ORDER BY           title_length_bucket;
 
END;
$BODY$
LANGUAGE PLPGSQL;
CREATE FUNCTION
Time: 1.375 ms
partition_test=# set auto_explain.log_min_duration to 0;
SET
Time: 0.190 ms
partition_test=# set auto_explain.log_nested_statements to true ;
SET
Time: 0.197 ms
partition_test=# select title_vs_review_plpgsql('2001-01-01',
'2001-12-31');title_vs_review_plpgsql 
-------------------------
(0 rows)

Time: 0.899 ms
partition_test=# select title_vs_review_sql('2001-01-01', '2001-12-31');title_vs_review_sql 
---------------------
(0 rows)

Time: 0.949 ms

When we check the logs for the query plans, I expect them both to only scan
the one child table, however:
< 2017-06-21 13:40:21.086 UTC > LOG:  duration: 0.013 ms  plan:Query Text: SELECT
width_bucket(length(product_title),1, 50, 5) title_length_bucket,        round(avg(review_rating), 2) AS
review_average,       count(*)    FROM       customer_reviews    WHERE        product_group = 'Book'        AND
review_dateBETWEEN start_date AND end_date    GROUP BY        title_length_bucket    ORDER BY
title_length_bucketGroupAggregate (cost=14.95..15.01 rows=2 width=44) (actual 
time=0.011..0.011 rows=0 loops=1)  Group Key: (width_bucket((length(customer_reviews.product_title))::double
precision, '1'::double precision, '50'::double precision, 5))  ->  Sort  (cost=14.95..14.95 rows=2 width=8) (actual
time=0.010..0.010
rows=0 loops=1)        Sort Key:
(width_bucket((length(customer_reviews.product_title))::double precision,
'1'::double precision, '50'::double precision, 5))        Sort Method: quicksort  Memory: 25kB        ->  Result
(cost=0.00..14.94rows=2 width=8) (actual 
time=0.005..0.005 rows=0 loops=1)              ->  Append  (cost=0.00..14.90 rows=2 width=36) (actual
time=0.004..0.004 rows=0 loops=1)                    ->  Seq Scan on customer_reviews  (cost=0.00..0.00
rows=1 width=36) (actual time=0.003..0.003 rows=0 loops=1)                          Filter: ((review_date >=
'2001-01-01'::date)AND 
(review_date <= '2001-12-31'::date) AND (product_group = 'Book'::text))                    ->  Seq Scan on
customer_reviews_2001 
(cost=0.00..14.90 rows=1 width=36) (actual time=0.000..0.000 rows=0
loops=1)                          Filter: ((review_date >= '2001-01-01'::date) AND
(review_date <= '2001-12-31'::date) AND (product_group = 'Book'::text))
< 2017-06-21 13:40:21.086 UTC > CONTEXT:  PL/pgSQL function
title_vs_review_plpgsql(date,date) line 3 at RETURN QUERY
< 2017-06-21 13:40:21.086 UTC > LOG:  duration: 0.640 ms  plan:Query Text: select title_vs_review_plpgsql('2001-01-01',
'2001-12-31');Result (cost=0.00..5.25 rows=1000 width=32) (actual time=0.636..0.636 
rows=0 loops=1)
< 2017-06-21 13:40:26.869 UTC > LOG:  duration: 0.030 ms  plan:Query Text: SELECT
width_bucket(length(product_title),1, 50, 5) title_length_bucket,    round(avg(review_rating), 2) AS review_average,
count(*)FROM  customer_reviewsWHERE    product_group = 'Book'    AND    review_date BETWEEN start_date AND
end_dateGROUPBY    title_length_bucketORDER BY    title_length_bucketGroupAggregate  (cost=74.68..74.88 rows=6
width=44)(actual 
time=0.028..0.028 rows=0 loops=1)  Group Key: (width_bucket((length(customer_reviews.product_title))::double
precision, '1'::double precision, '50'::double precision, 5))  ->  Sort  (cost=74.68..74.70 rows=6 width=8) (actual
time=0.026..0.026
rows=0 loops=1)        Sort Key:
(width_bucket((length(customer_reviews.product_title))::double precision,
'1'::double precision, '50'::double precision, 5))        Sort Method: quicksort  Memory: 25kB        ->  Result
(cost=0.00..74.61rows=6 width=8) (actual 
time=0.007..0.007 rows=0 loops=1)              ->  Append  (cost=0.00..74.50 rows=6 width=36) (actual
time=0.007..0.007 rows=0 loops=1)                    ->  Seq Scan on customer_reviews  (cost=0.00..0.00
rows=1 width=36) (actual time=0.003..0.003 rows=0 loops=1)                          Filter: ((review_date >= $1) AND
(review_date<= 
$2) AND (product_group = 'Book'::text))                    ->  Seq Scan on customer_reviews_2000
(cost=0.00..14.90 rows=1 width=36) (actual time=0.001..0.001 rows=0
loops=1)                          Filter: ((review_date >= $1) AND (review_date <=
$2) AND (product_group = 'Book'::text))                    ->  Seq Scan on customer_reviews_2001
(cost=0.00..14.90 rows=1 width=36) (actual time=0.001..0.001 rows=0
loops=1)                          Filter: ((review_date >= $1) AND (review_date <=
$2) AND (product_group = 'Book'::text))                    ->  Seq Scan on customer_reviews_2002
(cost=0.00..14.90 rows=1 width=36) (actual time=0.000..0.000 rows=0
loops=1)                          Filter: ((review_date >= $1) AND (review_date <=
$2) AND (product_group = 'Book'::text))                    ->  Seq Scan on customer_reviews_2003
(cost=0.00..14.90 rows=1 width=36) (actual time=0.001..0.001 rows=0
loops=1)                          Filter: ((review_date >= $1) AND (review_date <=
$2) AND (product_group = 'Book'::text))                    ->  Seq Scan on customer_reviews_2004
(cost=0.00..14.90 rows=1 width=36) (actual time=0.001..0.001 rows=0
loops=1)                          Filter: ((review_date >= $1) AND (review_date <=
$2) AND (product_group = 'Book'::text))
< 2017-06-21 13:40:26.869 UTC > CONTEXT:  SQL function "title_vs_review_sql"
statement 1
< 2017-06-21 13:40:26.869 UTC > LOG:  duration: 0.684 ms  plan:Query Text: select title_vs_review_sql('2001-01-01',
'2001-12-31');Result (cost=0.00..5.25 rows=1000 width=32) (actual time=0.680..0.680 
rows=0 loops=1)





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