The SORT operator enables you to sort the input data.
Example: Sorting the data in table t1, with column c1 sorted in descending order and column c2 in ascending order
obclient>CREATE TABLE t1(c1 INT, c2 INT);
Query OK, 0 rows affected (0.12 sec)
obclient>CREATE TABLE t2(c1 INT, c2 INT);
Query OK, 0 rows affected (0.12 sec)
obclient>EXPLAIN SELECT c1 FROM t1 ORDER BY c1 DESC, c2 ASC\G;
*************************** 1. row ***************************
Query Plan:
====================================
|ID|OPERATOR |NAME|EST. ROWS|COST|
------------------------------------
|0 |SORT | |3 |40 |
|1 | TABLE SCAN|t1 |3 |37 |
====================================
Outputs & filters:
-------------------------------------
0 - output([t1.c1]), filter(nil), sort_keys([t1.c1, DESC], [t1.c2, ASC])
1 - output([t1.c1], [t1.c2]), filter(nil),
access([t1.c1], [t1.c2]), partitions(p0)
In the preceding example, the function of SORT, the No. 0 operator in the execution plan display, is to sort data of table t1. The Outputs & filters section in the execution plan display shows in detail the output information of the SORT operator.
| Field | Description |
|---|---|
| output | The output columns of the operator. |
| filter | The filter predicates of the operator. In this example, the condition is set to nil because no filter is configured for the SORT operator. |
| sort_keys([column, DESC],[column, ASC] ...) | Sorts data by column. * DESC: In descending order. * ASC: In ascending order. For example, SORT keys in sort_keys([t1.c1, DESC],[t1.c2, ASC]) are c1 and c2. Column c1 is sorted in descending order and column c2 in ascending order. |
