谓词函数¶

谓词函数只返回true或false，通常用于WHERE子句中。

Nebula Graph 支持以下谓词函数。

函数	说明
exists()	如果指定的属性在点、边或映射中存在，则返回`true`，否则返回`false`。
any()	如果指定的谓词适用于列表中的至少一个元素，则返回`true`，否则返回`false`。
all()	如果指定的谓词适用于列表中的每个元素，则返回`true`，否则返回`false`。
none()	如果指定的谓词不适用于列表中的任何一个元素，则返回`true`，否则返回`false`。
single()	如果指定的谓词适用于列表中的唯一一个元素，则返回`true`，否则返回`false`。

Note

如果列表为空，或者列表中的所有元素都为空，则返回 NULL。

Compatibility

在 openCypher 中只定义了函数exists()，其他几个函数依赖于具体实现。

语法¶

<predicate>(<variable> IN <list> WHERE <condition>)

示例¶

nebula> RETURN any(n IN [1, 2, 3, 4, 5, NULL] \
        WHERE n > 2) AS r;
+------+
| r    |
+------+
| true |
+------+

nebula> RETURN single(n IN range(1, 5) \
        WHERE n == 3) AS r;
+------+
| r    |
+------+
| true |
+------+

nebula> RETURN none(n IN range(1, 3) \
        WHERE n == 0) AS r;
+------+
| r    |
+------+
| true |
+------+

nebula> WITH [1, 2, 3, 4, 5, NULL] AS a \
        RETURN any(n IN a WHERE n > 2);
+-------------------------+
| any(n IN a WHERE (n>2)) |
+-------------------------+
| true                    |
+-------------------------+

nebula> MATCH p = (n:player{name:"LeBron James"})<-[:follow]-(m) \
        RETURN nodes(p)[0].name AS n1, nodes(p)[1].name AS n2, \
        all(n IN nodes(p) WHERE n.name NOT STARTS WITH "D") AS b;
+----------------+-------------------+-------+
| n1             | n2                | b     |
+----------------+-------------------+-------+
| "LeBron James" | "Danny Green"     | false |
| "LeBron James" | "Dejounte Murray" | false |
| "LeBron James" | "Chris Paul"      | true  |
| "LeBron James" | "Kyrie Irving"    | true  |
| "LeBron James" | "Carmelo Anthony" | true  |
| "LeBron James" | "Dwyane Wade"     | false |
+----------------+-------------------+-------+

nebula> MATCH p = (n:player{name:"LeBron James"})-[:follow]->(m) \
        RETURN single(n IN nodes(p) WHERE n.age > 40) AS b;
+------+
| b    |
+------+
| true |
+------+

nebula> MATCH (n:player) \
        RETURN exists(n.id), n IS NOT NULL;
+--------------+---------------+
| exists(n.id) | n IS NOT NULL |
+--------------+---------------+
| false        | true          |
+--------------+---------------+
...

nebula> MATCH (n:player) \
        WHERE exists(n['name']) \
        RETURN n;
+---------------------------------------------------------------+
| n                                                             |
+---------------------------------------------------------------+
| ("player105" :player{age: 31, name: "Danny Green"})           |
| ("player109" :player{age: 34, name: "Tiago Splitter"})        |
| ("player111" :player{age: 38, name: "David West"})            |
...

最后更新: March 7, 2023