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MDEV-23908: Implement SELECT ... OFFSET ... FETCH ...

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This commit implements the standard SQL extension
OFFSET start { ROW | ROWS }
[FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } { ONLY | WITH TIES }]

To achieve this a reserved keyword OFFSET is introduced.

The general logic for WITH TIES implies:
1. The number of rows a query returns is no longer known during optimize
   phase. Adjust optimizations to no longer consider this.
2. During end_send make use of an "order Cached_item"to compare if the
   ORDER BY columns changed. Keep returning rows until there is a
   change. This happens only after we reached the row limit.
3. Within end_send_group, the order by clause was eliminated. It is
   still possible to keep the optimization of using end_send_group for
   producing the final result set.
This commit is contained in:
Vicențiu Ciorbaru
2021-03-28 21:41:50 +03:00
parent 2d595319bf
commit 299b935320
19 changed files with 2621 additions and 81 deletions
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16
sql/sql_limit.h
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@@ -23,20 +23,23 @@
class Select_limit_counters
{
ha_rows select_limit_cnt, offset_limit_cnt;
bool with_ties;
public:
Select_limit_counters():
select_limit_cnt(0), offset_limit_cnt(0)
select_limit_cnt(0), offset_limit_cnt(0), with_ties(false)
{};
Select_limit_counters(Select_limit_counters &orig):
Select_limit_counters(const Select_limit_counters &orig):
select_limit_cnt(orig.select_limit_cnt),
offset_limit_cnt(orig.offset_limit_cnt)
offset_limit_cnt(orig.offset_limit_cnt),
with_ties(orig.with_ties)
{};
void set_limit(ha_rows limit, ha_rows offset)
void set_limit(ha_rows limit, ha_rows offset, bool with_ties_arg)
{
offset_limit_cnt= offset;
select_limit_cnt= limit;
with_ties= with_ties_arg;
/*
Guard against an overflow condition, where limit + offset exceede
ha_rows value range. This case covers unreasonably large parameter
@@ -53,6 +56,7 @@ class Select_limit_counters
{
offset_limit_cnt= 0;
select_limit_cnt= 1;
with_ties= false;
}
bool is_unlimited() const
@@ -67,7 +71,7 @@ class Select_limit_counters
/* Reset the limit entirely. */
void clear()
{ select_limit_cnt= HA_POS_ERROR; offset_limit_cnt= 0; }
{ select_limit_cnt= HA_POS_ERROR; offset_limit_cnt= 0; with_ties= false;}
bool check_offset(ha_rows sent) const
{
@@ -79,6 +83,8 @@ class Select_limit_counters
{ return select_limit_cnt; }
ha_rows get_offset_limit() const
{ return offset_limit_cnt; }
bool is_with_ties() const
{ return with_ties; }
};
#endif // INCLUDES_MARIADB_SQL_LIMIT_H