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

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

示例

  1. nebula> RETURN any(n IN [1, 2, 3, 4, 5, NULL] \
  2.         WHERE n > 2) AS r;
  3. +------+
  4. | r    |
  5. +------+
  6. | true |
  7. +------+
  9. nebula> RETURN single(n IN range(1, 5) \
  10.         WHERE n == 3) AS r;
  11. +------+
  12. | r    |
  13. +------+
  14. | true |
  15. +------+
  17. nebula> RETURN none(n IN range(1, 3) \
  18.         WHERE n == 0) AS r;
  19. +------+
  20. | r    |
  21. +------+
  22. | true |
  23. +------+
  25. nebula> WITH [1, 2, 3, 4, 5, NULL] AS a \
  26.         RETURN any(n IN a WHERE n > 2);
  27. +-------------------------+
  28. | any(n IN a WHERE (n>2)) |
  29. +-------------------------+
  30. | true                    |
  31. +-------------------------+
  33. nebula> MATCH p = (n:player{name:"LeBron James"})<-[:follow]-(m) \
  34.         RETURN nodes(p)[0].name AS n1, nodes(p)[1].name AS n2, \
  35.         all(n IN nodes(p) WHERE n.name NOT STARTS WITH "D") AS b;
  36. +----------------+-------------------+-------+
  37. | n1             | n2                | b     |
  38. +----------------+-------------------+-------+
  39. | "LeBron James" | "Danny Green"     | false |
  40. | "LeBron James" | "Dejounte Murray" | false |
  41. | "LeBron James" | "Chris Paul"      | true  |
  42. | "LeBron James" | "Kyrie Irving"    | true  |
  43. | "LeBron James" | "Carmelo Anthony" | true  |
  44. | "LeBron James" | "Dwyane Wade"     | false |
  45. +----------------+-------------------+-------+
  47. nebula> MATCH p = (n:player{name:"LeBron James"})-[:follow]->(m) \
  48.         RETURN single(n IN nodes(p) WHERE n.age > 40) AS b;
  49. +------+
  50. | b    |
  51. +------+
  52. | true |
  53. +------+
  55. nebula> MATCH (n:player) \
  56.         RETURN exists(n.id), n IS NOT NULL;
  57. +--------------+---------------+
  58. | exists(n.id) | n IS NOT NULL |
  59. +--------------+---------------+
  60. | false        | true          |
  61. +--------------+---------------+
  62. ...
  64. nebula> MATCH (n:player) \
  65.         WHERE exists(n['name']) \
  66.         RETURN n;
  67. +---------------------------------------------------------------+
  68. | n                                                             |
  69. +---------------------------------------------------------------+
  70. | ("player105" :player{age: 31, name: "Danny Green"})           |
  71. | ("player109" :player{age: 34, name: "Tiago Splitter"})        |
  72. | ("player111" :player{age: 38, name: "David West"})            |
  73. ...

最后更新: November 1, 2021