Static Partition Pruning

MogDB determines when static pruning is used primarily based on static predicates.

If MogDB can identify which consecutive set of partitions was accessed at parsing time, the Selected Partitions column in the execution plan shows the start and end values of the partition being accessed. For any other partition pruning case (including dynamic partition pruning), MogDB displays Selected Partitions.

Static partition pruning is available via the EXPLAIN VERBOSE statement to view the execution plan. In the following example, there are four partitions in the prune_tt01 table. The query plan shows that partitions 3 and 4 are scanned by SeqScan. Therefore, it is judged that partitions 1 and 2 have been cut out.

MogDB=# \d+ prune_tt01
                      Table "public.prune_tt01"
 Column |  Type   | Modifiers | Storage | Stats target | Description 
--------+---------+-----------+---------+--------------+-------------
 a      | integer |           | plain   |              | 
 b      | integer |           | plain   |              | 
Indexes:
    "index_prune_tt01" btree (a) LOCAL TABLESPACE pg_default
Partition By RANGE(a)
Number of partitions: 4 (View pg_partition to check each partition range.)
Has OIDs: no
Options: orientation=row, compression=no

MogDB=# explain verbose select * from prune_tt01 where a>12;
                                             QUERY PLAN                                             
----------------------------------------------------------------------------------------------------
 Partition Iterator  (cost=13.80..27.75 rows=716 width=8)
   Output: a, b
   Iterations: 2
   Selected Partitions:  3..4
   ->  Partitioned Bitmap Heap Scan on public.prune_tt01  (cost=13.80..27.75 rows=716 width=8)
         Output: a, b
         Recheck Cond: (prune_tt01.a > 12)
         ->  Partitioned Bitmap Index Scan on index_prune_tt01  (cost=0.00..13.62 rows=716 width=0)
               Index Cond: (prune_tt01.a > 12)
(9 rows)

The detailed information for static partition pruning is shown in the following table.

Table 1 Detailed information for static partition pruning

No.	Constraint Name	Constraint Range
1	Partition table type	Range partition, list partition, and hash partition
2	Partition expression type	- A partition constraint can be a single expression, such as `a >12` - A partition constraint can be a BOOL expression, such as `a > 2 and a < 12` - A partition constraint can be an array, such as `a in (2, 3)` - A partition constraint can be a constant expression, such as `1 = 1` - A partition constraint can be the `Is (NOT)NULL` expression, such as `a IS NULL`
3	Partition expression operator	- Range partition table supports five operators, including `=`, `>`, `>=`, `<`, and `<=`. - List partition and hash partition supports only the `=` operator.
4	Partition expression parameter	One side is partition key, and the other side is constance, such as `a > 12`.
5	Second-level partition	Combination of range, list, and hash partition tables, such as Range-List partition table.
6	Partition pruning result	Explain verbose shows the pruned partition list.

Issue