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Update group-by.md (#2336)
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* Update group-by.md

* add example for group by to explain its implicit usage

* Update group-by.md

* Update group-by.md

* Update group-by.md

* Update group-by.md

* Update group-by.md

* Update group-by.md

* Update group-by.md
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abby-cyber authored Nov 22, 2022
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25 changes: 23 additions & 2 deletions docs-2.0/3.ngql-guide/8.clauses-and-options/group-by.md
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Expand Up @@ -57,8 +57,6 @@ nebula> GO FROM "player100" OVER follow BIDIRECT \
+---------------------+------------+
```

## 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 \
Expand All @@ -73,3 +71,26 @@ nebula> GO FROM "player100" OVER follow \
```

`sum()`函数详情请参见[内置数学函数](../6.functions-and-expressions/1.math.md)


## 隐式分组

在上述 nGQL 语句中明确写出`GROUP BY`并起到分组字段作用的用法称为`GROUP BY`显示用法;而在 openCypher 语句中`GROUP BY`的用法是隐式的,即在语句中不用写出`GROUP BY`也可起到分组字段的作用。nGQL 语句中显示地`GROUP BY`用法与 openCypher 语句中的隐式地`GROUP BY`用法相同,并且 nGQL 语句兼容 openCypher 的用法,即也支持隐式地使用`GROUP BY`。有关`GROUP BY`的隐式用法,请参见[how-to-make-group-by-in-a-cypher-query](https://stackoverflow.com/questions/52722671/how-to-make-group-by-in-a-cypher-query)

例如:查询 34 岁以上的球员中完全重叠服役的区间。

```ngql
nebula> LOOKUP ON player WHERE player.age > 34 YIELD id(vertex) AS v | \
GO FROM $-.v OVER serve YIELD serve.start_year AS start_year, serve.end_year AS end_year | \
YIELD $-.start_year, $-.end_year, count(*) AS count | \
ORDER BY $-.count DESC | LIMIT 5;
+---------------+-------------+-------+
| $-.start_year | $-.end_year | count |
+---------------+-------------+-------+
| 2018 | 2019 | 3 |
| 1998 | 2004 | 2 |
| 2012 | 2013 | 2 |
| 2007 | 2012 | 2 |
| 2010 | 2011 | 2 |
+---------------+-------------+-------+
```

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