Re: Add SPLIT PARTITION/MERGE PARTITIONS commands

hi.

+ /* Sort array of lower bounds. */
+ qsort_arg(lower_bounds, nparts, sizeof(PartitionRangeBound *),
+ qsort_partition_rbound_cmp, (void *) key);
here, we don't need ``(void *)``

+ALTER TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
+ MERGE PARTITIONS (<replaceable
class="parameter">partition_name1</replaceable>, <replaceable
class="parameter">partition_name2</replaceable> [, ...])
+ INTO <replaceable class="parameter">partition_name</replaceable>
In the synopsis section, we can combine the last two lines into one
for better formatting.

after
<varlistentry id="sql-altertable-parms-partition-name">
we can add the following to briefly explain parameters: partition_name1,
partition_name2

<varlistentry id="sql-altertable-parms-partition-name1">
<term><replaceable class="parameter">partition_name1</replaceable></term>
<term><replaceable class="parameter">partition_name2</replaceable></term>
<listitem>
<para>
The names of the tables being merged into the new partition.
</para>
</listitem>
</varlistentry>

What do you think about alternative syntax:
ALTER TABLE tab1 MERGE PARTITION part1 WITH (part2, part3) mentioned in [1].
I think we need to settle this issue before moving forward.
If the current MERGE PARTITION design is finalized, then v48-0001 looks solid.

[1] https://postgr.es/m/CA+TgmoY0=bT_xBP8csR=MFE=FxGE2n2-me2-31jBOgEcLvW7ug@mail.gmail.com