GROUP BY¶
GROUP BY子句可以用于聚合数据。
openCypher 兼容性¶
本文操作仅适用于原生 nGQL。
用户也可以使用 openCypher 方式的 count() 函数聚合数据。
ngql
nebula> MATCH (v:player)<-[:follow]-(:player) RETURN v.player.name AS Name, count(*) as cnt ORDER BY cnt DESC;
+----------------------+-----+
| Name | cnt |
+----------------------+-----+
| "Tim Duncan" | 10 |
| "LeBron James" | 6 |
| "Tony Parker" | 5 |
| "Chris Paul" | 4 |
| "Manu Ginobili" | 4 |
+----------------------+-----+
...
语法¶
GROUP BY子句可以聚合相同值的行，然后进行计数、排序和计算等操作。
GROUP BY子句可以在管道符（|）之后和YIELD子句之前使用。
ngql
| GROUP BY <var> YIELD <var>, <aggregation_function(var)>
aggregation_function()函数支持avg()、sum()、max()、min()、count()、collect()、std()。
示例¶
```ngql
查找所有连接到 player100 的点，并根据他们的姓名进行分组，返回姓名的出现次数。¶
nebula> GO FROM "player100" OVER follow BIDIRECT \ YIELD properties($$).name as Name \ | GROUP BY $-.Name \ YIELD $-.Name as Player, count(*) AS Name_Count; +---------------------+------------+ | Player | Name_Count | +---------------------+------------+ | "Shaquille O'Neal" | 1 | | "Tiago Splitter" | 1 | | "Manu Ginobili" | 2 | | "Boris Diaw" | 1 | | "LaMarcus Aldridge" | 1 | | "Tony Parker" | 2 | | "Marco Belinelli" | 1 | | "Dejounte Murray" | 1 | | "Danny Green" | 1 | | "Aron Baynes" | 1 | +---------------------+------------+ ```
用函数进行分组和计算¶
```ngql
查找所有连接到 player100 的点，并根据起始点进行分组，返回 degree 的总和。¶
nebula> GO FROM "player100" OVER follow \ YIELD src(edge) AS player, properties(edge).degree AS degree \ | GROUP BY \(-.player \ YIELD sum(\)-.degree); +----------------+ | sum($-.degree) | +----------------+ | 190 | +----------------+ ```
sum()函数详情请参见内置数学函数。