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select version();
version
PostgreSQL 12.9 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-4), 64-bit
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CREATE TABLE tab ( version INT PRIMARY KEY, col_A TEXT, col_B TEXT, col_C TEXT );
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INSERT INTO tab (version, col_A, col_B, col_C) VALUES (1, 'A1', 'B1', null), (2, 'A2', 'B2', null), (3, 'A3', 'B3', null), (4, 'A5', null, 'C1'), (5, 'A1', null, null);
5 rows affected
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SELECT * FROM tab ORDER BY version;
version col_a col_b col_c
1 A1 B1
2 A2 B2
3 A3 B3
4 A5 C1
5 A1
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-- Quassnoi Option 1 SELECT ( SELECT col_a FROM tab WHERE col_a IS NOT NULL ORDER BY version DESC LIMIT 1 ), ( SELECT col_b FROM tab WHERE col_b IS NOT NULL ORDER BY version DESC LIMIT 1 ), ( SELECT col_c FROM tab WHERE col_c IS NOT NULL ORDER BY version DESC LIMIT 1 ) ;
col_a col_b col_c
A1 B3 C1
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-- Quassnoi Option 2 SELECT a.col_a, b.col_b, c.col_c FROM ( SELECT last_a, last_b, last_c FROM ( SELECT *, MAX(version) FILTER (WHERE col_a IS NOT NULL) OVER w AS last_a, MAX(version) FILTER (WHERE col_b IS NOT NULL) OVER w AS last_b, MAX(version) FILTER (WHERE col_c IS NOT NULL) OVER w AS last_c FROM tab WINDOW w AS (ORDER BY version DESC) ) q WHERE (last_a, last_b, last_c) IS NOT NULL ORDER BY version DESC LIMIT 1 ) q JOIN tab a ON a.version = q.last_a JOIN tab b ON b.version = q.last_b JOIN tab c ON c.version = q.last_c ;
col_a col_b col_c
A1 B3 C1
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-- J.D. SELECT DISTINCT FIRST_VALUE(col_A) OVER (ORDER BY CASE WHEN col_A IS NULL THEN 0 ELSE version END DESC) AS LastA, FIRST_VALUE(col_B) OVER (ORDER BY CASE WHEN col_B IS NULL THEN 0 ELSE version END DESC) AS LastB, FIRST_VALUE(col_C) OVER (ORDER BY CASE WHEN col_C IS NULL THEN 0 ELSE version END DESC) AS LastC FROM tab ;
lasta lastb lastc
A1 B3 C1
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create or replace function test_get_lnn () returns table(col_A text, col_B text, col_C text) language plpgsql as $$ declare t_a text := null; t_b text := null; t_c text := null; r record; begin for r in select t.col_A, t.col_B, t.col_C from tab t order by version desc loop if t_a is null then t_a := r.col_A; end if; if t_b is null then t_b := r.col_B; end if; if t_c is null then t_c := r.col_C; end if; exit when t_a is not null and t_b is not null and t_c is not null; end loop; return query select t_a, t_b, t_c; end; $$ ; -- Gerard H. Pille select * from test_get_lnn() ;
col_a col_b col_c
A1 B3 C1
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-- Gerard H. Pille select * from test_get_lnn() ;
col_a col_b col_c
A1 B3 C1
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-- adding 1k rows with some nulls insert into tab (version, col_A, col_B, col_C) select i, case when random() < 0.5 then (random()*100)::int end, case when random() < 0.5 then (random()*100)::int end, case when random() < 0.5 then (random()*100)::int end from generate_series(6, 1000) as g(i) ;
995 rows affected
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create unique index uq_version on tab (version) ;
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select 'Performance Analysis (EXPLAIN (ANALYZE, TIMING OFF) below' ;
?column?
Performance Analysis (EXPLAIN (ANALYZE, TIMING OFF) below
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-- Quassnoi Option 1 EXPLAIN (ANALYZE, TIMING OFF) SELECT ( SELECT col_a FROM tab WHERE col_a IS NOT NULL ORDER BY version DESC LIMIT 1 ), ( SELECT col_b FROM tab WHERE col_b IS NOT NULL ORDER BY version DESC LIMIT 1 ), ( SELECT col_c FROM tab WHERE col_c IS NOT NULL ORDER BY version DESC LIMIT 1 ) ;
QUERY PLAN
Result (cost=0.99..1.00 rows=1 width=96) (actual rows=1 loops=1)
InitPlan 1 (returns $0)
-> Limit (cost=0.28..0.33 rows=1 width=36) (actual rows=1 loops=1)
-> Index Scan Backward using uq_version on tab (cost=0.28..55.27 rows=995 width=36) (actual rows=1 loops=1)
Filter: (col_a IS NOT NULL)
InitPlan 2 (returns $1)
-> Limit (cost=0.28..0.33 rows=1 width=36) (actual rows=1 loops=1)
-> Index Scan Backward using uq_version on tab tab_1 (cost=0.28..55.27 rows=995 width=36) (actual rows=1 loops=1)
Filter: (col_b IS NOT NULL)
Rows Removed by Filter: 2
InitPlan 3 (returns $2)
-> Limit (cost=0.28..0.33 rows=1 width=36) (actual rows=1 loops=1)
-> Index Scan Backward using uq_version on tab tab_2 (cost=0.28..55.27 rows=995 width=36) (actual rows=1 loops=1)
Filter: (col_c IS NOT NULL)
Rows Removed by Filter: 1
Planning Time: 0.373 ms
Execution Time: 0.090 ms
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-- Quassnoi Option 2 EXPLAIN (ANALYZE, TIMING OFF) SELECT a.col_a, b.col_b, c.col_c FROM ( SELECT last_a, last_b, last_c FROM ( SELECT *, MAX(version) FILTER (WHERE col_a IS NOT NULL) OVER w AS last_a, MAX(version) FILTER (WHERE col_b IS NOT NULL) OVER w AS last_b, MAX(version) FILTER (WHERE col_c IS NOT NULL) OVER w AS last_c FROM tab WINDOW w AS (ORDER BY version DESC) ) q WHERE (last_a, last_b, last_c) IS NOT NULL ORDER BY version DESC LIMIT 1 ) q JOIN tab a ON a.version = q.last_a JOIN tab b ON b.version = q.last_b JOIN tab c ON c.version = q.last_c
QUERY PLAN
Nested Loop (cost=1.10..25.30 rows=1 width=96) (actual rows=1 loops=1)
-> Nested Loop (cost=0.83..16.99 rows=1 width=68) (actual rows=1 loops=1)
-> Nested Loop (cost=0.55..8.68 rows=1 width=40) (actual rows=1 loops=1)
-> Limit (cost=0.28..0.36 rows=1 width=16) (actual rows=1 loops=1)
-> Subquery Scan on q (cost=0.28..85.28 rows=985 width=16) (actual rows=1 loops=1)
Filter: ((q.last_a IS NOT NULL) AND (q.last_b IS NOT NULL) AND (q.last_c IS NOT NULL))
Rows Removed by Filter: 2
-> WindowAgg (cost=0.28..75.28 rows=1000 width=112) (actual rows=3 loops=1)
-> Index Scan Backward using uq_version on tab (cost=0.28..55.27 rows=1000 width=100) (actual rows=4 loops=1)
-> Index Scan using uq_version on tab a (cost=0.28..8.29 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_a)
-> Index Scan using uq_version on tab b (cost=0.28..8.29 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_b)
-> Index Scan using uq_version on tab c (cost=0.28..8.29 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_c)
Planning Time: 0.406 ms
Execution Time: 0.231 ms
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-- J.D. EXPLAIN (ANALYZE, TIMING OFF) SELECT DISTINCT FIRST_VALUE(col_A) OVER (ORDER BY CASE WHEN col_A IS NULL THEN 0 ELSE version END DESC) AS LastA, FIRST_VALUE(col_B) OVER (ORDER BY CASE WHEN col_B IS NULL THEN 0 ELSE version END DESC) AS LastB, FIRST_VALUE(col_C) OVER (ORDER BY CASE WHEN col_C IS NULL THEN 0 ELSE version END DESC) AS LastC FROM tab ;
QUERY PLAN
HashAggregate (cost=224.49..226.49 rows=200 width=108) (actual rows=1 loops=1)
Group Key: first_value(col_a) OVER (?), (first_value(col_b) OVER (?)), (first_value(col_c) OVER (?))
-> WindowAgg (cost=199.49..216.99 rows=1000 width=108) (actual rows=1000 loops=1)
-> Sort (cost=199.49..201.99 rows=1000 width=172) (actual rows=1000 loops=1)
Sort Key: (CASE WHEN (col_a IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 103kB
-> WindowAgg (cost=132.16..149.66 rows=1000 width=172) (actual rows=1000 loops=1)
-> Sort (cost=132.16..134.66 rows=1000 width=140) (actual rows=1000 loops=1)
Sort Key: (CASE WHEN (col_b IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 99kB
-> WindowAgg (cost=64.83..82.33 rows=1000 width=140) (actual rows=1000 loops=1)
-> Sort (cost=64.83..67.33 rows=1000 width=108) (actual rows=1000 loops=1)
Sort Key: (CASE WHEN (col_c IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 88kB
-> Seq Scan on tab (cost=0.00..15.00 rows=1000 width=108) (actual rows=1000 loops=1)
Planning Time: 0.064 ms
Execution Time: 5.091 ms
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-- Gerard H. Pille EXPLAIN (ANALYZE, TIMING OFF) select * from test_get_lnn() ;
QUERY PLAN
Function Scan on test_get_lnn (cost=0.25..10.25 rows=1000 width=96) (actual rows=1 loops=1)
Planning Time: 0.014 ms
Execution Time: 0.174 ms
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-- adding 20k rows with nulls insert into tab (version, col_A, col_B, col_C) select i, null, null, null from generate_series(1001, 20000) as g(i) ;
19000 rows affected
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-- Quassnoi Option 1 EXPLAIN (ANALYZE, TIMING OFF) SELECT ( SELECT col_a FROM tab WHERE col_a IS NOT NULL ORDER BY version DESC LIMIT 1 ), ( SELECT col_b FROM tab WHERE col_b IS NOT NULL ORDER BY version DESC LIMIT 1 ), ( SELECT col_c FROM tab WHERE col_c IS NOT NULL ORDER BY version DESC LIMIT 1 ) ;
QUERY PLAN
Result (cost=1.01..1.02 rows=1 width=96) (actual rows=1 loops=1)
InitPlan 1 (returns $0)
-> Limit (cost=0.29..0.34 rows=1 width=36) (actual rows=1 loops=1)
-> Index Scan Backward using uq_version on tab (cost=0.29..858.29 rows=17910 width=36) (actual rows=1 loops=1)
Filter: (col_a IS NOT NULL)
Rows Removed by Filter: 19000
InitPlan 2 (returns $1)
-> Limit (cost=0.29..0.34 rows=1 width=36) (actual rows=1 loops=1)
-> Index Scan Backward using uq_version on tab tab_1 (cost=0.29..858.29 rows=17910 width=36) (actual rows=1 loops=1)
Filter: (col_b IS NOT NULL)
Rows Removed by Filter: 19002
InitPlan 3 (returns $2)
-> Limit (cost=0.29..0.34 rows=1 width=36) (actual rows=1 loops=1)
-> Index Scan Backward using uq_version on tab tab_2 (cost=0.29..858.29 rows=17910 width=36) (actual rows=1 loops=1)
Filter: (col_c IS NOT NULL)
Rows Removed by Filter: 19001
Planning Time: 0.186 ms
Execution Time: 8.887 ms
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-- Quassnoi Option 2 EXPLAIN (ANALYZE, TIMING OFF) SELECT a.col_a, b.col_b, c.col_c FROM ( SELECT last_a, last_b, last_c FROM ( SELECT *, MAX(version) FILTER (WHERE col_a IS NOT NULL) OVER w AS last_a, MAX(version) FILTER (WHERE col_b IS NOT NULL) OVER w AS last_b, MAX(version) FILTER (WHERE col_c IS NOT NULL) OVER w AS last_c FROM tab WINDOW w AS (ORDER BY version DESC) ) q WHERE (last_a, last_b, last_c) IS NOT NULL ORDER BY version DESC LIMIT 1 ) q JOIN tab a ON a.version = q.last_a JOIN tab b ON b.version = q.last_b JOIN tab c ON c.version = q.last_c ;
QUERY PLAN
Nested Loop (cost=1.15..25.29 rows=1 width=96) (actual rows=1 loops=1)
-> Nested Loop (cost=0.86..16.99 rows=1 width=68) (actual rows=1 loops=1)
-> Nested Loop (cost=0.57..8.68 rows=1 width=40) (actual rows=1 loops=1)
-> Limit (cost=0.29..0.37 rows=1 width=16) (actual rows=1 loops=1)
-> Subquery Scan on q (cost=0.29..1398.29 rows=17731 width=16) (actual rows=1 loops=1)
Filter: ((q.last_a IS NOT NULL) AND (q.last_b IS NOT NULL) AND (q.last_c IS NOT NULL))
Rows Removed by Filter: 19002
-> WindowAgg (cost=0.29..1218.29 rows=18000 width=112) (actual rows=19003 loops=1)
-> Index Scan Backward using uq_version on tab (cost=0.29..858.29 rows=18000 width=100) (actual rows=19004 loops=1)
-> Index Scan using uq_version on tab a (cost=0.29..8.30 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_a)
-> Index Scan using uq_version on tab b (cost=0.29..8.30 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_b)
-> Index Scan using uq_version on tab c (cost=0.29..8.30 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_c)
Planning Time: 0.327 ms
Execution Time: 13.012 ms
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-- J.D. EXPLAIN (ANALYZE, TIMING OFF) SELECT DISTINCT FIRST_VALUE(col_A) OVER (ORDER BY CASE WHEN col_A IS NULL THEN 0 ELSE version END DESC) AS LastA, FIRST_VALUE(col_B) OVER (ORDER BY CASE WHEN col_B IS NULL THEN 0 ELSE version END DESC) AS LastB, FIRST_VALUE(col_C) OVER (ORDER BY CASE WHEN col_C IS NULL THEN 0 ELSE version END DESC) AS LastC FROM tab ;
QUERY PLAN
HashAggregate (cost=5166.64..5184.64 rows=1800 width=108) (actual rows=1 loops=1)
Group Key: first_value(col_a) OVER (?), (first_value(col_b) OVER (?)), (first_value(col_c) OVER (?))
-> WindowAgg (cost=4716.64..5031.64 rows=18000 width=108) (actual rows=20000 loops=1)
-> Sort (cost=4716.64..4761.64 rows=18000 width=172) (actual rows=20000 loops=1)
Sort Key: (CASE WHEN (col_a IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 2331kB
-> WindowAgg (cost=3129.43..3444.43 rows=18000 width=172) (actual rows=20000 loops=1)
-> Sort (cost=3129.43..3174.43 rows=18000 width=140) (actual rows=20000 loops=1)
Sort Key: (CASE WHEN (col_b IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 1734kB
-> WindowAgg (cost=1542.21..1857.21 rows=18000 width=140) (actual rows=20000 loops=1)
-> Sort (cost=1542.21..1587.21 rows=18000 width=108) (actual rows=20000 loops=1)
Sort Key: (CASE WHEN (col_c IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 1722kB
-> Seq Scan on tab (cost=0.00..270.00 rows=18000 width=108) (actual rows=20000 loops=1)
Planning Time: 0.069 ms
Execution Time: 50.184 ms
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-- Gerard H. Pille EXPLAIN (ANALYZE, TIMING OFF) select * from test_get_lnn() ;
QUERY PLAN
Function Scan on test_get_lnn (cost=0.25..10.25 rows=1000 width=96) (actual rows=1 loops=1)
Planning Time: 0.037 ms
Execution Time: 37.447 ms
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create index ix_va on tab (version) WHERE (col_a IS NOT NULL) ; create index ix_vb on tab (version) WHERE (col_b IS NOT NULL) ; create index ix_vc on tab (version) WHERE (col_c IS NOT NULL) ; select 'Adding partial indexes: (version) WHERE (column IS NOT NULL)'
?column?
Adding partial indexes: (version) WHERE (column IS NOT NULL)
 hidden batch(es)


-- Quassnoi Option 1 EXPLAIN (ANALYZE, TIMING OFF) SELECT ( SELECT col_a FROM tab WHERE col_a IS NOT NULL ORDER BY version DESC LIMIT 1 ), ( SELECT col_b FROM tab WHERE col_b IS NOT NULL ORDER BY version DESC LIMIT 1 ), ( SELECT col_c FROM tab WHERE col_c IS NOT NULL ORDER BY version DESC LIMIT 1 ) ;
QUERY PLAN
Result (cost=0.91..0.92 rows=1 width=96) (actual rows=1 loops=1)
InitPlan 1 (returns $0)
-> Limit (cost=0.28..0.30 rows=1 width=36) (actual rows=1 loops=1)
-> Index Scan Backward using ix_va on tab (cost=0.28..577.84 rows=19900 width=36) (actual rows=1 loops=1)
InitPlan 2 (returns $1)
-> Limit (cost=0.28..0.30 rows=1 width=36) (actual rows=1 loops=1)
-> Index Scan Backward using ix_vb on tab tab_1 (cost=0.28..577.84 rows=19900 width=36) (actual rows=1 loops=1)
InitPlan 3 (returns $2)
-> Limit (cost=0.27..0.30 rows=1 width=36) (actual rows=1 loops=1)
-> Index Scan Backward using ix_vc on tab tab_2 (cost=0.27..577.78 rows=19900 width=36) (actual rows=1 loops=1)
Planning Time: 0.645 ms
Execution Time: 0.153 ms
 hidden batch(es)


-- Quassnoi Option 2 EXPLAIN (ANALYZE, TIMING OFF) SELECT a.col_a, b.col_b, c.col_c FROM ( SELECT last_a, last_b, last_c FROM ( SELECT *, MAX(version) FILTER (WHERE col_a IS NOT NULL) OVER w AS last_a, MAX(version) FILTER (WHERE col_b IS NOT NULL) OVER w AS last_b, MAX(version) FILTER (WHERE col_c IS NOT NULL) OVER w AS last_c FROM tab WINDOW w AS (ORDER BY version DESC) ) q WHERE (last_a, last_b, last_c) IS NOT NULL ORDER BY version DESC LIMIT 1 ) q JOIN tab a ON a.version = q.last_a JOIN tab b ON b.version = q.last_b JOIN tab c ON c.version = q.last_c ;
QUERY PLAN
Nested Loop (cost=1.15..25.29 rows=1 width=96) (actual rows=1 loops=1)
-> Nested Loop (cost=0.86..16.98 rows=1 width=68) (actual rows=1 loops=1)
-> Nested Loop (cost=0.57..8.68 rows=1 width=40) (actual rows=1 loops=1)
-> Limit (cost=0.29..0.36 rows=1 width=16) (actual rows=1 loops=1)
-> Subquery Scan on q (cost=0.29..1488.29 rows=19701 width=16) (actual rows=1 loops=1)
Filter: ((q.last_a IS NOT NULL) AND (q.last_b IS NOT NULL) AND (q.last_c IS NOT NULL))
Rows Removed by Filter: 19002
-> WindowAgg (cost=0.29..1288.29 rows=20000 width=112) (actual rows=19003 loops=1)
-> Index Scan Backward using uq_version on tab (cost=0.29..888.29 rows=20000 width=100) (actual rows=19004 loops=1)
-> Index Scan using uq_version on tab a (cost=0.29..8.30 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_a)
-> Index Scan using uq_version on tab b (cost=0.29..8.30 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_b)
-> Index Scan using uq_version on tab c (cost=0.29..8.30 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_c)
Planning Time: 0.529 ms
Execution Time: 16.311 ms
 hidden batch(es)


-- J.D. EXPLAIN (ANALYZE, TIMING OFF) SELECT DISTINCT FIRST_VALUE(col_A) OVER (ORDER BY CASE WHEN col_A IS NULL THEN 0 ELSE version END DESC) AS LastA, FIRST_VALUE(col_B) OVER (ORDER BY CASE WHEN col_B IS NULL THEN 0 ELSE version END DESC) AS LastB, FIRST_VALUE(col_C) OVER (ORDER BY CASE WHEN col_C IS NULL THEN 0 ELSE version END DESC) AS LastC FROM tab ;
QUERY PLAN
HashAggregate (cost=5776.31..5796.31 rows=2000 width=108) (actual rows=1 loops=1)
Group Key: first_value(col_a) OVER (?), (first_value(col_b) OVER (?)), (first_value(col_c) OVER (?))
-> WindowAgg (cost=5276.31..5626.31 rows=20000 width=108) (actual rows=20000 loops=1)
-> Sort (cost=5276.31..5326.31 rows=20000 width=172) (actual rows=20000 loops=1)
Sort Key: (CASE WHEN (col_a IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 2331kB
-> WindowAgg (cost=3497.54..3847.54 rows=20000 width=172) (actual rows=20000 loops=1)
-> Sort (cost=3497.54..3547.54 rows=20000 width=140) (actual rows=20000 loops=1)
Sort Key: (CASE WHEN (col_b IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 1734kB
-> WindowAgg (cost=1718.77..2068.77 rows=20000 width=140) (actual rows=20000 loops=1)
-> Sort (cost=1718.77..1768.77 rows=20000 width=108) (actual rows=20000 loops=1)
Sort Key: (CASE WHEN (col_c IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 1722kB
-> Seq Scan on tab (cost=0.00..290.00 rows=20000 width=108) (actual rows=20000 loops=1)
Planning Time: 0.080 ms
Execution Time: 48.109 ms
 hidden batch(es)


-- Gerard H. Pille EXPLAIN (ANALYZE, TIMING OFF) select * from test_get_lnn() ;
QUERY PLAN
Function Scan on test_get_lnn (cost=0.25..10.25 rows=1000 width=96) (actual rows=1 loops=1)
Planning Time: 0.036 ms
Execution Time: 36.740 ms
 hidden batch(es)


create index ix_version_include_a on tab (version) INCLUDE (col_a) WHERE (col_a IS NOT NULL) ; create index ix_version_include_b on tab (version) INCLUDE (col_b) WHERE (col_b IS NOT NULL) ; create index ix_version_include_c on tab (version) INCLUDE (col_c) WHERE (col_c IS NOT NULL) ; select 'Adding partial indexex: (version) INCLUDE (column) WHERE (column IS NOT NULL)'
?column?
Adding partial indexex: (version) INCLUDE (column) WHERE (column IS NOT NULL)
 hidden batch(es)


-- Quassnoi Option 1 EXPLAIN (ANALYZE, TIMING OFF) SELECT ( SELECT col_a FROM tab WHERE col_a IS NOT NULL ORDER BY version DESC LIMIT 1 ), ( SELECT col_b FROM tab WHERE col_b IS NOT NULL ORDER BY version DESC LIMIT 1 ), ( SELECT col_c FROM tab WHERE col_c IS NOT NULL ORDER BY version DESC LIMIT 1 ) ;
QUERY PLAN
Result (cost=0.91..0.92 rows=1 width=96) (actual rows=1 loops=1)
InitPlan 1 (returns $0)
-> Limit (cost=0.28..0.30 rows=1 width=36) (actual rows=1 loops=1)
-> Index Only Scan Backward using ix_version_include_a on tab (cost=0.28..577.84 rows=19900 width=36) (actual rows=1 loops=1)
Heap Fetches: 1
InitPlan 2 (returns $1)
-> Limit (cost=0.28..0.30 rows=1 width=36) (actual rows=1 loops=1)
-> Index Only Scan Backward using ix_version_include_b on tab tab_1 (cost=0.28..577.84 rows=19900 width=36) (actual rows=1 loops=1)
Heap Fetches: 1
InitPlan 3 (returns $2)
-> Limit (cost=0.27..0.30 rows=1 width=36) (actual rows=1 loops=1)
-> Index Only Scan Backward using ix_version_include_c on tab tab_2 (cost=0.27..577.78 rows=19900 width=36) (actual rows=1 loops=1)
Heap Fetches: 1
Planning Time: 0.455 ms
Execution Time: 0.124 ms
 hidden batch(es)


-- Quassnoi Option 2 EXPLAIN (ANALYZE, TIMING OFF) SELECT a.col_a, b.col_b, c.col_c FROM ( SELECT last_a, last_b, last_c FROM ( SELECT *, MAX(version) FILTER (WHERE col_a IS NOT NULL) OVER w AS last_a, MAX(version) FILTER (WHERE col_b IS NOT NULL) OVER w AS last_b, MAX(version) FILTER (WHERE col_c IS NOT NULL) OVER w AS last_c FROM tab WINDOW w AS (ORDER BY version DESC) ) q WHERE (last_a, last_b, last_c) IS NOT NULL ORDER BY version DESC LIMIT 1 ) q JOIN tab a ON a.version = q.last_a JOIN tab b ON b.version = q.last_b JOIN tab c ON c.version = q.last_c ;
QUERY PLAN
Nested Loop (cost=1.15..25.29 rows=1 width=96) (actual rows=1 loops=1)
-> Nested Loop (cost=0.86..16.98 rows=1 width=68) (actual rows=1 loops=1)
-> Nested Loop (cost=0.57..8.68 rows=1 width=40) (actual rows=1 loops=1)
-> Limit (cost=0.29..0.36 rows=1 width=16) (actual rows=1 loops=1)
-> Subquery Scan on q (cost=0.29..1488.29 rows=19701 width=16) (actual rows=1 loops=1)
Filter: ((q.last_a IS NOT NULL) AND (q.last_b IS NOT NULL) AND (q.last_c IS NOT NULL))
Rows Removed by Filter: 19002
-> WindowAgg (cost=0.29..1288.29 rows=20000 width=112) (actual rows=19003 loops=1)
-> Index Scan Backward using uq_version on tab (cost=0.29..888.29 rows=20000 width=100) (actual rows=19004 loops=1)
-> Index Scan using uq_version on tab a (cost=0.29..8.30 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_a)
-> Index Scan using uq_version on tab b (cost=0.29..8.30 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_b)
-> Index Scan using uq_version on tab c (cost=0.29..8.30 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_c)
Planning Time: 0.334 ms
Execution Time: 12.051 ms
 hidden batch(es)


-- J.D. EXPLAIN (ANALYZE, TIMING OFF) SELECT DISTINCT FIRST_VALUE(col_A) OVER (ORDER BY CASE WHEN col_A IS NULL THEN 0 ELSE version END DESC) AS LastA, FIRST_VALUE(col_B) OVER (ORDER BY CASE WHEN col_B IS NULL THEN 0 ELSE version END DESC) AS LastB, FIRST_VALUE(col_C) OVER (ORDER BY CASE WHEN col_C IS NULL THEN 0 ELSE version END DESC) AS LastC FROM tab ;
QUERY PLAN
HashAggregate (cost=5776.31..5796.31 rows=2000 width=108) (actual rows=1 loops=1)
Group Key: first_value(col_a) OVER (?), (first_value(col_b) OVER (?)), (first_value(col_c) OVER (?))
-> WindowAgg (cost=5276.31..5626.31 rows=20000 width=108) (actual rows=20000 loops=1)
-> Sort (cost=5276.31..5326.31 rows=20000 width=172) (actual rows=20000 loops=1)
Sort Key: (CASE WHEN (col_a IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 2331kB
-> WindowAgg (cost=3497.54..3847.54 rows=20000 width=172) (actual rows=20000 loops=1)
-> Sort (cost=3497.54..3547.54 rows=20000 width=140) (actual rows=20000 loops=1)
Sort Key: (CASE WHEN (col_b IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 1734kB
-> WindowAgg (cost=1718.77..2068.77 rows=20000 width=140) (actual rows=20000 loops=1)
-> Sort (cost=1718.77..1768.77 rows=20000 width=108) (actual rows=20000 loops=1)
Sort Key: (CASE WHEN (col_c IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 1722kB
-> Seq Scan on tab (cost=0.00..290.00 rows=20000 width=108) (actual rows=20000 loops=1)
Planning Time: 0.108 ms
Execution Time: 48.914 ms
 hidden batch(es)


-- Gerard H. Pille EXPLAIN (ANALYZE, TIMING OFF) select * from test_get_lnn() ;
QUERY PLAN
Function Scan on test_get_lnn (cost=0.25..10.25 rows=1000 width=96) (actual rows=1 loops=1)
Planning Time: 0.036 ms
Execution Time: 37.143 ms
 hidden batch(es)


-- update with some non-null in the last 100 rows update tab set col_a = case when random() < 0.1 then (random()*100)::int end, col_b = case when random() < 0.1 then (random()*100)::int end, col_c = case when random() < 0.1 then (random()*100)::int end from generate_series(19900, 20000) as g(i) where tab.version = g.i ;
101 rows affected
 hidden batch(es)


-- Quassnoi Option 1 EXPLAIN (ANALYZE, TIMING OFF) SELECT ( SELECT col_a FROM tab WHERE col_a IS NOT NULL ORDER BY version DESC LIMIT 1 ), ( SELECT col_b FROM tab WHERE col_b IS NOT NULL ORDER BY version DESC LIMIT 1 ), ( SELECT col_c FROM tab WHERE col_c IS NOT NULL ORDER BY version DESC LIMIT 1 ) ;
QUERY PLAN
Result (cost=0.91..0.92 rows=1 width=96) (actual rows=1 loops=1)
InitPlan 1 (returns $0)
-> Limit (cost=0.28..0.30 rows=1 width=36) (actual rows=1 loops=1)
-> Index Only Scan Backward using ix_version_include_a on tab (cost=0.28..577.84 rows=19900 width=36) (actual rows=1 loops=1)
Heap Fetches: 1
InitPlan 2 (returns $1)
-> Limit (cost=0.28..0.30 rows=1 width=36) (actual rows=1 loops=1)
-> Index Only Scan Backward using ix_version_include_b on tab tab_1 (cost=0.28..577.84 rows=19900 width=36) (actual rows=1 loops=1)
Heap Fetches: 1
InitPlan 3 (returns $2)
-> Limit (cost=0.27..0.30 rows=1 width=36) (actual rows=1 loops=1)
-> Index Only Scan Backward using ix_version_include_c on tab tab_2 (cost=0.27..577.78 rows=19900 width=36) (actual rows=1 loops=1)
Heap Fetches: 1
Planning Time: 0.222 ms
Execution Time: 0.050 ms
 hidden batch(es)


-- Quassnoi Option 2 EXPLAIN (ANALYZE, TIMING OFF) SELECT a.col_a, b.col_b, c.col_c FROM ( SELECT last_a, last_b, last_c FROM ( SELECT *, MAX(version) FILTER (WHERE col_a IS NOT NULL) OVER w AS last_a, MAX(version) FILTER (WHERE col_b IS NOT NULL) OVER w AS last_b, MAX(version) FILTER (WHERE col_c IS NOT NULL) OVER w AS last_c FROM tab WINDOW w AS (ORDER BY version DESC) ) q WHERE (last_a, last_b, last_c) IS NOT NULL ORDER BY version DESC LIMIT 1 ) q JOIN tab a ON a.version = q.last_a JOIN tab b ON b.version = q.last_b JOIN tab c ON c.version = q.last_c ;
QUERY PLAN
Nested Loop (cost=1.15..25.29 rows=1 width=96) (actual rows=1 loops=1)
-> Nested Loop (cost=0.86..16.98 rows=1 width=68) (actual rows=1 loops=1)
-> Nested Loop (cost=0.57..8.68 rows=1 width=40) (actual rows=1 loops=1)
-> Limit (cost=0.29..0.36 rows=1 width=16) (actual rows=1 loops=1)
-> Subquery Scan on q (cost=0.29..1488.29 rows=19701 width=16) (actual rows=1 loops=1)
Filter: ((q.last_a IS NOT NULL) AND (q.last_b IS NOT NULL) AND (q.last_c IS NOT NULL))
Rows Removed by Filter: 22
-> WindowAgg (cost=0.29..1288.29 rows=20000 width=112) (actual rows=23 loops=1)
-> Index Scan Backward using uq_version on tab (cost=0.29..888.29 rows=20000 width=100) (actual rows=24 loops=1)
-> Index Scan using uq_version on tab a (cost=0.29..8.30 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_a)
-> Index Scan using uq_version on tab b (cost=0.29..8.30 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_b)
-> Index Scan using uq_version on tab c (cost=0.29..8.30 rows=1 width=36) (actual rows=1 loops=1)
Index Cond: (version = q.last_c)
Planning Time: 0.347 ms
Execution Time: 0.112 ms
 hidden batch(es)


-- J.D. EXPLAIN (ANALYZE, TIMING OFF) SELECT DISTINCT FIRST_VALUE(col_A) OVER (ORDER BY CASE WHEN col_A IS NULL THEN 0 ELSE version END DESC) AS LastA, FIRST_VALUE(col_B) OVER (ORDER BY CASE WHEN col_B IS NULL THEN 0 ELSE version END DESC) AS LastB, FIRST_VALUE(col_C) OVER (ORDER BY CASE WHEN col_C IS NULL THEN 0 ELSE version END DESC) AS LastC FROM tab ;
QUERY PLAN
HashAggregate (cost=5776.31..5796.31 rows=2000 width=108) (actual rows=1 loops=1)
Group Key: first_value(col_a) OVER (?), (first_value(col_b) OVER (?)), (first_value(col_c) OVER (?))
-> WindowAgg (cost=5276.31..5626.31 rows=20000 width=108) (actual rows=20000 loops=1)
-> Sort (cost=5276.31..5326.31 rows=20000 width=172) (actual rows=20000 loops=1)
Sort Key: (CASE WHEN (col_a IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 2331kB
-> WindowAgg (cost=3497.54..3847.54 rows=20000 width=172) (actual rows=20000 loops=1)
-> Sort (cost=3497.54..3547.54 rows=20000 width=140) (actual rows=20000 loops=1)
Sort Key: (CASE WHEN (col_b IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 1735kB
-> WindowAgg (cost=1718.77..2068.77 rows=20000 width=140) (actual rows=20000 loops=1)
-> Sort (cost=1718.77..1768.77 rows=20000 width=108) (actual rows=20000 loops=1)
Sort Key: (CASE WHEN (col_c IS NULL) THEN 0 ELSE version END) DESC
Sort Method: quicksort Memory: 1723kB
-> Seq Scan on tab (cost=0.00..290.00 rows=20000 width=108) (actual rows=20000 loops=1)
Planning Time: 0.086 ms
Execution Time: 49.105 ms
 hidden batch(es)


-- Gerard H. Pille EXPLAIN (ANALYZE, TIMING OFF) select * from test_get_lnn() ;
QUERY PLAN
Function Scan on test_get_lnn (cost=0.25..10.25 rows=1000 width=96) (actual rows=1 loops=1)
Planning Time: 0.036 ms
Execution Time: 0.168 ms
 hidden batch(es)