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How-to-get-result-set-suitable-for-graph-visualisation.md
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# How to get result set suitable for graph visualisation
# How to get a result set suitable for graph visualisation
There are some [requirements for result sets][1] if you want to build a graph.
Here is an example of building a query that returns a result set appropriate for graph visualisation.
There are some [requirements for result sets][1] if you want to make a graph.
Here is an example of building a query that returns a result set appropriate for graph
visualisation.
Let's say, you have 2 tables:
house:
| name | points |
| ---------- | ------ |
| Gryffindor | 100 |
| Hufflepuff | 90 |
| Ravenclaw | 95 |
| Slytherin | 80 |
1. `house`:
student:
| id | name | house |
| -- | -------------- | ---------- |
| 1 | Harry Potter | Gryffindor |
| 2 | Ron Weasley | Gryffindor |
| 3 | Draco Malfoy' | Slytherin |
| 4 | Luna Lovegood | Ravenclaw |
| 5 | Cedric Diggory | Hufflepuff |
| name | points |
| ---------- | ------ |
| Gryffindor | 100 |
| Hufflepuff | 90 |
| Ravenclaw | 95 |
| Slytherin | 80 |
2. `student`:
| id | name | house |
| -- | -------------- | ---------- |
| 1 | Harry Potter | Gryffindor |
| 2 | Ron Weasley | Gryffindor |
| 3 | Draco Malfoy' | Slytherin |
| 4 | Luna Lovegood | Ravenclaw |
| 5 | Cedric Diggory | Hufflepuff |
Each student belongs to a certain house.
Let's say you want to build a graph with houses and students as nodes, where each house is linked with its students.
Let's say you want to build a graph with houses and students as nodes, where each house is linked
with its students.
We are going to use [json_object][2] function to form JSONs. The result set should contain both nodes and edges
and we have to provide a field indicating if the record represents a node (0) or and edge (1).
Let's provide it as 'object_type':
We are going to use [json_object][2] function to form JSON documents. The result set should contain
both nodes and edges and we have to provide a field indicating if the document represents a node
(0) or and edge (1). Let's provide it as `object_type`:
```sql
SELECT json_object('object_type', 0)
@@ -39,11 +43,13 @@ UNION ALL
SELECT json_object('object_type', 1)
FROM student
```
Note that we included `student` table twice. That is because the table contains not only students but also their relationship to houses.
So the records from the first union of `student` will be used as nodes and from the second one - as edges.
Then we need to provide an ID for each node. Let's put it in `node_id` field.
The `node_id` value for students is taken from `id` column and for houses - from `name`:
Note that we included `student` table twice. That is because the table contains not only students
but also their relationship to houses. So the records from the first union of `student` are used
as nodes and from the second one - as edges.
Then we need to provide an ID for each node. Let's put it in `node_id` field. The `node_id` value
for students is taken from `id` column and for houses - from `name`:
```sql
SELECT json_object('object_type', 0, 'node_id', name)
@@ -56,7 +62,8 @@ SELECT json_object('object_type', 1)
FROM student
```
Each edge record must provide a node id where the edge starts and where it ends. Let's put it in `source` and `target`:
Each edge document must provide a node id where the edge begins and where it ends. Let's put it in
`source` and `target`:
```sql
SELECT json_object('object_type', 0, 'node_id', name)
@@ -68,12 +75,13 @@ UNION ALL
SELECT json_object('object_type', 1, 'source', house, 'target', id)
FROM student
```
Basically, that is enough to build a graph. But it won't be meaningful without labels.
Basically, that is enough to build a graph. But it is not very meaningful without labels.
Also, it would be nice to distinguish house nodes from student nodes by color.
Let's put additional fields `label` and `type` that can be used in graph styling.
```sql
SELECT json_object('object_type', 0, 'node_id', name, 'label', name, 'type', 'house')
SELECT json_object('object_type', 0, 'node_id', name, 'label', name, 'type', 'house') AS graph_object
FROM house
UNION ALL
SELECT json_object('object_type', 0, 'node_id', id, 'label', name, 'type', 'student')
@@ -85,7 +93,7 @@ FROM student
Run the query, the result set will look like this:
| json_object('object_type', 0, 'node_id', name, 'label', name, 'type', 'house') |
| graph_object |
| ------------------------------------------------------------------------------ |
| {"object_type":0,"node_id":"Gryffindor","label":"Gryffindor","type":"house"} |
| {"object_type":0,"node_id":"Hufflepuff","label":"Hufflepuff","type":"house"} |
@@ -102,8 +110,8 @@ Run the query, the result set will look like this:
| {"object_type":1,"node_source":"Ravenclaw","target":4} |
| {"object_type":1,"node_source":"Hufflepuff","target":5} |
Now in the graph editor, we can set mapping of the result set records into node and edge properties,
set graph styles and get the following visualisation:
Now in the graph editor, we can set mapping of the result set documents into node and edge
properties, set graph styles and get the following visualisation:
![Fig. 1: Graph visualisation example](./img/Screenshot_potter_example.png)