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| author | Vicențiu Ciorbaru <vicentiu@mariadb.org> | 2021-03-28 21:41:50 +0300 |
|---|---|---|
| committer | Vicențiu Ciorbaru <vicentiu@mariadb.org> | 2021-04-21 14:09:14 +0300 |
| commit | 299b93532036152ef47d6fa140199e2fc01dfecb (patch) | |
| tree | deda241b116124f0e7363410e454072a5cc7f68b /sql/sql_limit.h | |
| parent | 2d595319bf542dcdeeb058139efa2ef54f645c7b (diff) | |
| download | mariadb-git-299b93532036152ef47d6fa140199e2fc01dfecb.tar.gz | |
MDEV-23908: Implement SELECT ... OFFSET ... FETCH ...
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.
Diffstat (limited to 'sql/sql_limit.h')
| -rw-r--r-- | sql/sql_limit.h | 16 |
1 files changed, 11 insertions, 5 deletions
diff --git a/sql/sql_limit.h b/sql/sql_limit.h index 60034201a50..b51ebf72493 100644 --- a/sql/sql_limit.h +++ b/sql/sql_limit.h @@ -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 |