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new 50d3f47 Update count function
50d3f47 is described below
commit 50d3f47ca10ce169d4e1bc17c7811da6ab31dce3
Author: Josh Innis <[email protected]>
AuthorDate: Thu Oct 21 12:51:54 2021 -0700
Update count function
---
docs/functions/aggregate_functions.md | 51 +++++++++++++++++++++++++++--------
1 file changed, 40 insertions(+), 11 deletions(-)
diff --git a/docs/functions/aggregate_functions.md
b/docs/functions/aggregate_functions.md
index ec5de12..4d62053 100644
--- a/docs/functions/aggregate_functions.md
+++ b/docs/functions/aggregate_functions.md
@@ -3,7 +3,7 @@
## min()
-min() returns the minimum value in a set of values. \
+min() returns the minimum value in a set of values.
Syntax: `min(expression)`
@@ -555,18 +555,14 @@ Arguments:
Considerations:
-
-
-
* count(*) includes records returning null.
* count(expr) ignores null values.
* count(null) returns 0.
* Using count(*) to return the number of nodes
* count(*) can be used to return the number of nodes; for example, the number
of nodes connected to some node n.
-Query
-
+Query
```
SELECT *
FROM cypher('graph_name', $$
@@ -575,12 +571,9 @@ FROM cypher('graph_name', $$
$$ as (age agtype, number_of_people agtype);
```
-
The labels and age property of the start node n and the number of nodes
related to n are returned.
Result:
-
-
<table>
<tr>
<td>age
@@ -604,8 +597,6 @@ Result:
Using count(*) to group and count relationship typescount(*) can be used to
group relationship types and return the number.
Query
-
-
```
SELECT *
FROM cypher('graph_name', $$
@@ -716,6 +707,44 @@ Result:
</table>
+### Counting with and without duplicates
+
+In this example we are trying to find all our friends of friends, and count
them:
+* The first aggregate function, count(DISTINCT friend_of_friend), will only
count a friend_of_friend once, as DISTINCT removes the duplicates.
+* The second aggregate function, count(friend_of_friend), will consider the
same friend_of_friend multiple times.
+
+Query
+```
+SELECT *
+FROM cypher('graph_name', $$
+ MATCH (me:Person)-[]->(friend:Person)-[]->(friend_of_friend:Person)
+ WHERE me.name = 'A'
+ RETURN count(DISTINCT friend_of_friend), count(friend_of_friend)
+$$) as (friend_of_friends_distinct agtype, friend_of_friends agtype);
+```
+
+Both B and C know D and thus D will get counted twice when not using DISTINCT
+
+Result:
+<table>
+ <tr>
+ <td>friend_of_friends_distinct
+ </td>
+ <td>friend_of_friends
+ </td>
+ </tr>
+ <tr>
+ <td>1
+ </td>
+ <td>2
+ </td>
+ </tr>
+ <tr>
+ <td>1 row
+ </td>
+ </tr>
+</table>
+
## avg()
