使用内置的SELECT进行查询

你现在有了一个有数据的图!您可以运行一些简单的内置查询来检查数据。

选择顶点

下面的GSQL命令报告person顶点的总数。person.csv数据文件标题行后有7行。

GSQL command

SELECT count() FROM person

类似地，下面的GSQL命令报告friendship边的总数。friendship.csv文件在标题行后也有7行。

GSQL command

SELECT count() FROM person-(friendship)->person

结果如下所示:

GSQL > SELECT count() FROM person
[{
 "count": 7,
 "v_type": "person"
}]
GSQL > SELECT count() FROM person-(friendship)->person
[{
 "count": 14,
 "e_type": "friendship"
}]
GSQL >

边数

为什么有14条边?对于无向边，GSQL实际上创建两条边，每个方向一条

如果您想查看关于特定顶点集的详细信息，可以使用“SELECT *”和WHERE子句来指定谓词条件。以下是一些可以尝试的语句:

GSQL command

SELECT * FROM person WHERE primary_id=="Tom"
SELECT name FROM person WHERE state=="ca"
SELECT name, age FROM person WHERE age > 30

结果是JSON格式，如下所示：

GSQL shell

GSQL > SELECT * FROM person WHERE primary_id=="Tom"
[{
 "v_id": "Tom",
 "attributes": {
   "gender": "male",
   "name": "Tom",
   "state": "ca",
   "age": 40
 },
 "v_type": "person"
}]
GSQL > SELECT name FROM person WHERE state=="ca"
[
 {
   "v_id": "Amily",
   "attributes": {"name": "Amily"},
   "v_type": "person"
 },
 {
   "v_id": "Tom",
   "attributes": {"name": "Tom"},
   "v_type": "person"
 }
]
GSQL > SELECT name, age FROM person WHERE age > 30
[
 {
   "v_id": "Tom",
   "attributes": {
     "name": "Tom",
     "age": 40
   },
   "v_type": "person"
 },
 {
   "v_id": "Dan",
   "attributes": {
     "name": "Dan",
     "age": 34
   },
   "v_type": "person"
 }
]

选择边

以同样的方式，我们可以看到关于边的细节。为了描述一个边，您可以在三个部分中指定顶点和边的类型，并添加一些标点符号来表示遍历方向:

GSQL syntax

source_type -(edge_type)-> target_type

注意，无论是无向边还是有向边，总是使用箭头->。这是因为我们描述的是查询在图中的遍历(搜索)方向，而不是边本身的方向。

我们可以在WHERE子句中使用from_id谓词，从由“from_id”标识的顶点选择所有friendship边。关键字ANY表示允许任何边缘类型或任何目标顶点类型。以下两个查询的结果相同.

GSQL command

SELECT * FROM person-(friendship)->person WHERE from_id =="Tom"
SELECT * FROM person-(ANY)->ANY WHERE from_id =="Tom"

对内置边选择查询的限制

为了防止查询可能返回过多的输出项，内置边查询有以下限制:

1. 必须指定源顶点类型

2. 必须指定from_id条件

用户定义查询没有这样的限制。

结果如下所示：

GSQL

GSQL > SELECT * FROM person-(friendship)->person WHERE from_id =="Tom"
[
 {
   "from_type": "person",
   "to_type": "person",
   "directed": false,
   "from_id": "Tom",
   "to_id": "Dan",
   "attributes": {"connect_day": "2017-06-03 00:00:00"},
   "e_type": "friendship"
 },
 {
   "from_type": "person",
   "to_type": "person",
   "directed": false,
   "from_id": "Tom",
   "to_id": "Jenny",
   "attributes": {"connect_day": "2015-01-01 00:00:00"},
   "e_type": "friendship"
 }

另一种检查图大小的方法是使用管理员工具gadmin的选项之一。从Linux shell中输入命令：

#Linux shell

gadmin status graph -v

#Linux shell

[tigergraph@localhost ~]$ gadmin status graph -v
verbose is ON
=== graph ===
[m1    ][GRAPH][MSG ] Graph was loaded (/usr/local/tigergraph/gstore/0/part/): partition size is 4.00KiB, SchemaVersion: 0, VertexCount: 7, NumOfSkippedVertices: 0, NumOfDeletedVertices: 0, EdgeCount: 14
[m1    ][GRAPH][INIT] True
[INFO  ][GRAPH][MSG ] Above vertex and edge counts are for internal use which show approximate topology size of the local graph partition. Use DML to get the correct graph topology information
[SUMMARY][GRAPH] graph is ready