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Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.
create table test(ID,Start_date_time,End_date_time,class)
as values
(131, '5/26/2021 11:42', '5/26/2021 12:42', 'AAA')
,(132, '5/26/2021 12:42', '5/26/2021 13:18', 'AAA')
,(113, '5/26/2021 12:44', '5/26/2021 13:19', 'AAA')
,(114, '5/26/2021 13:19', '5/26/2021 13:34', 'AAA')
,(115, '5/26/2021 13:34', '5/26/2021 13:44', 'AAA')
,(111, '5/26/2021 16:09', '5/26/2021 17:24', 'AAA')
,(112, '5/26/2021 17:24', '5/26/2021 18:09', 'AAA')
,(123, '5/26/2021 8:08', '5/26/2021 10:08', 'BBB')
,(124, '5/26/2021 10:08', '5/26/2021 11:08', 'BBB')
,(116, '5/26/2021 11:06', '5/26/2021 11:30', 'BBB')
,(117, '5/26/2021 11:30', '5/26/2021 12:18', 'BBB')
,(118, '5/26/2021 12:18', '5/26/2021 13:06', 'BBB')
,(128, '5/26/2021 9:03', '5/26/2021 9:48', 'CCC')
,(129, '5/26/2021 9:48', '5/26/2021 10:03', 'CCC')
,(130, '5/26/2021 10:03', '5/26/2021 10:13', 'CCC')
,(119, '5/26/2021 10:22', '5/26/2021 10:34', 'CCC')
,(120, '5/26/2021 10:34', '5/26/2021 10:58', 'CCC')
,(121, '5/26/2021 10:58', '5/26/2021 11:10', 'CCC')
,(122, '5/26/2021 11:10', '5/26/2021 11:22', 'CCC')
,(125, '5/26/2021 14:47', '5/26/2021 15:47', 'DDD')
,(126, '5/26/2021 15:47', '5/26/2021 16:35', 'DDD')
,(127, '5/26/2021 16:35', '5/26/2021 17:35', 'DDD')
;
table test;
SELECT 22
| id | start_date_time | end_date_time | class |
|---|---|---|---|
| 131 | 5/26/2021 11:42 | 5/26/2021 12:42 | AAA |
| 132 | 5/26/2021 12:42 | 5/26/2021 13:18 | AAA |
| 113 | 5/26/2021 12:44 | 5/26/2021 13:19 | AAA |
| 114 | 5/26/2021 13:19 | 5/26/2021 13:34 | AAA |
| 115 | 5/26/2021 13:34 | 5/26/2021 13:44 | AAA |
| 111 | 5/26/2021 16:09 | 5/26/2021 17:24 | AAA |
| 112 | 5/26/2021 17:24 | 5/26/2021 18:09 | AAA |
| 123 | 5/26/2021 8:08 | 5/26/2021 10:08 | BBB |
| 124 | 5/26/2021 10:08 | 5/26/2021 11:08 | BBB |
| 116 | 5/26/2021 11:06 | 5/26/2021 11:30 | BBB |
| 117 | 5/26/2021 11:30 | 5/26/2021 12:18 | BBB |
| 118 | 5/26/2021 12:18 | 5/26/2021 13:06 | BBB |
| 128 | 5/26/2021 9:03 | 5/26/2021 9:48 | CCC |
| 129 | 5/26/2021 9:48 | 5/26/2021 10:03 | CCC |
| 130 | 5/26/2021 10:03 | 5/26/2021 10:13 | CCC |
| 119 | 5/26/2021 10:22 | 5/26/2021 10:34 | CCC |
| 120 | 5/26/2021 10:34 | 5/26/2021 10:58 | CCC |
| 121 | 5/26/2021 10:58 | 5/26/2021 11:10 | CCC |
| 122 | 5/26/2021 11:10 | 5/26/2021 11:22 | CCC |
| 125 | 5/26/2021 14:47 | 5/26/2021 15:47 | DDD |
| 126 | 5/26/2021 15:47 | 5/26/2021 16:35 | DDD |
| 127 | 5/26/2021 16:35 | 5/26/2021 17:35 | DDD |
SELECT 22
create table example_result(ID,Start_date_time,End_date_time,class,Updated_ID)
as values
(131, '5/26/2021 11:42', '5/26/2021 12:42', 'AAA', 131)
,(132, '5/26/2021 12:42', '5/26/2021 13:18', 'AAA', 131)
,(113, '5/26/2021 12:44', '5/26/2021 13:19', 'AAA', 113)
,(114, '5/26/2021 13:19', '5/26/2021 13:34', 'AAA', 113)
,(115, '5/26/2021 13:34', '5/26/2021 13:44', 'AAA', 113)
,(111, '5/26/2021 16:09', '5/26/2021 17:24', 'AAA', 111)
,(112, '5/26/2021 17:24', '5/26/2021 18:09', 'AAA', 111)
,(123, '5/26/2021 8:08', '5/26/2021 10:08', 'BBB', 123)
,(124, '5/26/2021 10:08', '5/26/2021 11:08', 'BBB', 123)
,(116, '5/26/2021 11:06', '5/26/2021 11:30', 'BBB', 116)
,(117, '5/26/2021 11:30', '5/26/2021 12:18', 'BBB', 116)
,(118, '5/26/2021 12:18', '5/26/2021 13:06', 'BBB', 116)
,(128, '5/26/2021 9:03', '5/26/2021 9:48', 'CCC', 128)
,(129, '5/26/2021 9:48', '5/26/2021 10:03', 'CCC', 128)
,(130, '5/26/2021 10:03', '5/26/2021 10:13', 'CCC', 128)
,(119, '5/26/2021 10:22', '5/26/2021 10:34', 'CCC', 119)
,(120, '5/26/2021 10:34', '5/26/2021 10:58', 'CCC', 119)
,(121, '5/26/2021 10:58', '5/26/2021 11:10', 'CCC', 119)
,(122, '5/26/2021 11:10', '5/26/2021 11:22', 'CCC', 119)
,(125, '5/26/2021 14:47', '5/26/2021 15:47', 'DDD', 125)
,(126, '5/26/2021 15:47', '5/26/2021 16:35', 'DDD', 125)
,(127, '5/26/2021 16:35', '5/26/2021 17:35', 'DDD', 125)
;
table example_result;
SELECT 22
| id | start_date_time | end_date_time | class | updated_id |
|---|---|---|---|---|
| 131 | 5/26/2021 11:42 | 5/26/2021 12:42 | AAA | 131 |
| 132 | 5/26/2021 12:42 | 5/26/2021 13:18 | AAA | 131 |
| 113 | 5/26/2021 12:44 | 5/26/2021 13:19 | AAA | 113 |
| 114 | 5/26/2021 13:19 | 5/26/2021 13:34 | AAA | 113 |
| 115 | 5/26/2021 13:34 | 5/26/2021 13:44 | AAA | 113 |
| 111 | 5/26/2021 16:09 | 5/26/2021 17:24 | AAA | 111 |
| 112 | 5/26/2021 17:24 | 5/26/2021 18:09 | AAA | 111 |
| 123 | 5/26/2021 8:08 | 5/26/2021 10:08 | BBB | 123 |
| 124 | 5/26/2021 10:08 | 5/26/2021 11:08 | BBB | 123 |
| 116 | 5/26/2021 11:06 | 5/26/2021 11:30 | BBB | 116 |
| 117 | 5/26/2021 11:30 | 5/26/2021 12:18 | BBB | 116 |
| 118 | 5/26/2021 12:18 | 5/26/2021 13:06 | BBB | 116 |
| 128 | 5/26/2021 9:03 | 5/26/2021 9:48 | CCC | 128 |
| 129 | 5/26/2021 9:48 | 5/26/2021 10:03 | CCC | 128 |
| 130 | 5/26/2021 10:03 | 5/26/2021 10:13 | CCC | 128 |
| 119 | 5/26/2021 10:22 | 5/26/2021 10:34 | CCC | 119 |
| 120 | 5/26/2021 10:34 | 5/26/2021 10:58 | CCC | 119 |
| 121 | 5/26/2021 10:58 | 5/26/2021 11:10 | CCC | 119 |
| 122 | 5/26/2021 11:10 | 5/26/2021 11:22 | CCC | 119 |
| 125 | 5/26/2021 14:47 | 5/26/2021 15:47 | DDD | 125 |
| 126 | 5/26/2021 15:47 | 5/26/2021 16:35 | DDD | 125 |
| 127 | 5/26/2021 16:35 | 5/26/2021 17:35 | DDD | 125 |
SELECT 22