谓词函数¶
谓词函数只返回true
或false
,通常用于WHERE
子句中。
NebulaGraph 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].player.name AS n1, nodes(p)[1].player.name AS n2, \
all(n IN nodes(p) WHERE n.player.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.player.age > 40) AS b;
+------+
| b |
+------+
| true |
+------+
nebula> MATCH (n:player) \
RETURN exists(n.player.id), n IS NOT NULL;
+---------------------+---------------+
| exists(n.player.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:
September 4, 2023