SELECT DISTINCT的SurrealDB等价

Question

我有一张表，上面列出的课程是RELATEd by requires_prerequisite和其他课程。我试图获得课程的二级先决条件依赖性(以课程作为先决条件的课程)，我有一个查询如下：

SELECT id, <-requires_prerequisite<-course<-requires_prerequisite<-course AS indirect_postrequisites
FROM course WHERE id = course:APS105;

这给了我这个：

[
  {
    "time": "526.8µs",
    "status": "OK",
    "result": [
      {
        "id": "course:APS105",
        "indirect_postrequisites": [
          "course:ECE345",
          "course:ECE297",
          "course:ECE344",
          "course:ECE295",
          "course:ECE345",
          "course:ECE297",
          "course:ECE344",
          "course:ECE295"
        ]
      }
    ]
  }
]

但是，正如您所注意到的，这里有重复的条目。我如何过滤掉重复的条目？在标准SQL中，我将使用

SELECT DISTINCT `in` FROM requires_prerequisite
WHERE `out` IN (SELECT `in` FROM requires_prerequisite WHERE `out`='APS105';

但如果我试着用

SELECT DISTINCT id, <-requires_prerequisite<-course<-requires_prerequisite<-course AS indirect_postrequisites
FROM course WHERE id = course:APS105;

然后我得到

{
  "code": 400,
  "details": "Request problems detected",
  "description": "There is a problem with your request. Refer to the documentation for further information.",
  "information": "There was a problem with the database: Parse error on line 1 at character 0 when parsing 'SELECT DISTINCT id, <-requires_prerequisite<-course<-requires_prerequisite<-course AS indirect_postr'"
}

如何筛选出重复的值？

如果你想知道副本为什么会出现，那是因为

RELATE course:ECE297->requires_prerequisite->course:APS105;
RELATE course:ECE297->requires_prerequisite->course:ECE244;
RELATE course:ECE244->requires_prerequisite->course:APS105;

Answer 1

在搜索完文档之后，我找到了array::distinct() function，它做了我想做的事情：

SELECT id, array::distinct(<-requires_prerequisite<-course<-requires_prerequisite<-course) AS indirect_postrequisites FROM course WHERE id = course:APS105;

[
  {
    "time": "537.8µs",
    "status": "OK",
    "result": [
      {
        "id": "course:APS105",
        "indirect_postrequisites": [
          "course:ECE345",
          "course:ECE297",
          "course:ECE344",
          "course:ECE295"
        ]
      }
    ]
  }
]