3.4 KiB
3.4 KiB
查询中使用聚合函数
聚合函数扫描一组记录，然后返回单行记录。这组记录可以是一个表或者视图、或者一个子查询的结果。OceanBase 支持的聚合函数详情请参考手册《OceanBase SQL参考（MySQL模式）》。
聚合函数通常跟 GROUP BY 子句一起使用，按照一个或多个列的值分组，然后每组返回单笔记录。
示例：分组统计每个仓库的销售额
MySQL 租户中，聚合函数跟 GROUP BY 子句一起使用的时候，对 select_list 里的列没有要求。这个可能会导致结果集很奇怪。如果要求 select_list 里的列跟 GROUP BY 子句中的列保持一致，需要设置 MySQL 命令行下的 sql_mode 为 'ONLY_FULL_GROUP_BY'。SQL 查询如下：
obclient> SELECT ol_w_id
, count(*) order_count
, sum(ol_amount) sum_amount
, round(avg(ol_amount),2) avg_amount
, min(ol_amount) min_amount
,max(ol_amount) max_amount
FROM ordl
GROUP BY ol_w_id
ORDER BY ol_w_id ;
+---------+-------------+------------+------------+------------+------------+
| ol_w_id | order_count | sum_amount | avg_amount | min_amount | max_amount |
+---------+-------------+------------+------------+------------+------------+
| 1 | 297 | 917174.33 | 3088.13 | 0.00 | 9876.11 |
| 2 | 329 | 1153354.23 | 3505.64 | 0.00 | 9979.34 |
+---------+-------------+------------+------------+------------+------------+
2 rows in set (0.01 sec)
obclient> SELECT ol_w_id, ol_d_id
, count(*) order_count
, sum(ol_amount) sum_amount
, round(avg(ol_amount),2) avg_amount
, min(ol_amount) min_amount
, max(ol_amount) max_amount
FROM ordl
GROUP BY ol_w_id
ORDER BY ol_w_id
;
+---------+---------+-------------+------------+------------+------------+------------+
| ol_w_id | ol_d_id | order_count | sum_amount | avg_amount | min_amount | max_amount |
+---------+---------+-------------+------------+------------+------------+------------+
| 1 | 1 | 297 | 917174.33 | 3088.13 | 0.00 | 9876.11 |
| 2 | 1 | 329 | 1153354.23 | 3505.64 | 0.00 | 9979.34 |
+---------+---------+-------------+------------+------------+------------+------------+
2 rows in set (0.00 sec)
obclient> show variables like '%sql_mode%';
+---------------+-------------------------------------------------------+
| Variable_name | Value |
+---------------+-------------------------------------------------------+
| sql_mode | PIPES_AS_CONCAT,STRICT_TRANS_TABLES,STRICT_ALL_TABLES |
+---------------+-------------------------------------------------------+
1 row in set (0.00 sec)
obclient> SET SESSION sql_mode='STRICT_ALL_TABLES,ONLY_FULL_GROUP_BY'; Query OK, 0 rows affected (0.00 sec)
obclient> SELECT ol_w_id, ol_d_id
, count(*) order_count
, sum(ol_amount) sum_amount
, round(avg(ol_amount),2) avg_amount
, min(ol_amount) min_amount
, max(ol_amount) max_amount
FROM ordl
GROUP BY ol_w_id
ORDER BY ol_w_id
;
ERROR 1055 (42000): 'tpccdb.ordl.ol_d_id' is not in GROUP BY
obclient>