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collect 函数

collect()函数返回一个符合表达式返回结果的列表。该函数可以将多条记录或值合并进一个列表,实现数据聚合。

collect()是一个聚合函数,类似 SQL 中的GROUP BY

示例

nebula> UNWIND [1, 2, 1] AS a \
        RETURN a;
+---+
| a |
+---+
| 1 |
| 2 |
| 1 |
+---+

nebula> UNWIND [1, 2, 1] AS a \
        RETURN collect(a);
+------------+
| collect(a) |
+------------+
| [1, 2, 1]  |
+------------+

nebula> UNWIND [1, 2, 1] AS a \
        RETURN a, collect(a), size(collect(a));
+---+------------+------------------+
| a | collect(a) | size(collect(a)) |
+---+------------+------------------+
| 2 | [2]        | 1                |
| 1 | [1, 1]     | 2                |
+---+------------+------------------+

# 降序排列,限制输出行数为 3,然后将结果输出到列表中。
nebula> UNWIND ["c", "b", "a", "d" ] AS p \
        WITH p AS q \
        ORDER BY q DESC LIMIT 3 \
        RETURN collect(q);
+-----------------+
| collect(q)      |
+-----------------+
| ["d", "c", "b"] |
+-----------------+

nebula> WITH [1, 1, 2, 2] AS coll \
        UNWIND coll AS x \
        WITH DISTINCT x \
        RETURN collect(x) AS ss;
+--------+
| ss     |
+--------+
| [1, 2] |
+--------+

nebula> MATCH (n:player) \
        RETURN collect(n.age);
+---------------------------------------------------------------+
| collect(n.age)                                                |
+---------------------------------------------------------------+
| [32, 32, 34, 29, 41, 40, 33, 25, 40, 37, ...
...

# 基于年龄聚合姓名。
nebula> MATCH (n:player) \
        RETURN n.age AS age, collect(n.name);
+-----+--------------------------------------------------------------------------+
| age | collect(n.name)                                                          |
+-----+--------------------------------------------------------------------------+
| 24  | ["Giannis Antetokounmpo"]                                                |
| 20  | ["Luka Doncic"]                                                          |
| 25  | ["Joel Embiid", "Kyle Anderson"]                                         |
+-----+--------------------------------------------------------------------------+
...

最后更新: November 24, 2021
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