Filter with pattern expressions documentation (#1425)

* Add pattern expressions

* Apply suggestions from code review

---------

Co-authored-by: Matea Pesic <80577904+matea16@users.noreply.github.com>

Author: Josipmrden

pages/querying/clauses/where.md

@@ -22,7 +22,8 @@ order to avoid problems with performance or results.
    1.4. [Filter with node properties](#14-filter-with-node-properties)<br />
    1.5. [Filter with relationship properties](#15-filter-with-relationship-properties)<br />
    1.6. [Check if property is not null](#16-check-if-property-is-not-null)<br />
-   1.7. [Filter with pattern expressions](#17-filter-with-pattern-expressions)<br />
+   1.7. [Filter with EXISTS expressions](#17-filter-with-exists-expressions)<br />
+   1.8. [Filter with pattern expressions](#18-filter-with-pattern-expressions)<br />
 2. [String matching](#2-string-matching)<br />
 3. [Regular Expressions](#3-regular-expressions)
 4. [Existential subqueries](#4-existential-subqueries)<br />
@@ -166,9 +167,9 @@ Output:
 +----------------+----------------+
 ```
 
-### 1.7. Filter with pattern expressions
+### 1.7. Filter with EXISTS expressions
 
-Currently, we support pattern expression filters with the `exists(pattern)`
+Currently, we support `EXISTS` expression filters with the `exists(pattern)`
 function, which can perform filters based on neighboring entities:
 
 ```cypher
@@ -191,6 +192,30 @@ Output:
 +----------------+
 ```
 
+### 1.8. Filter with pattern expressions
+
+Currently, we support pattern expression filters inside the `WHERE` clause.
+
+```cypher
+MATCH (p:Person)
+WHERE (p)-[:LIVING_IN]->(:Country {name: 'Germany'})
+RETURN p.name
+ORDER BY p.name;
+```
+
+Output:
+
+```nocopy
++----------------+
+| c.name         |
++----------------+
+| Anna           |
+| John           |
++----------------+
+```
+
+The pattern expressions can't contain any additional symbols that are not introduced in the previously matched symbols.
+
 ## 2. String matching
 
 Apart from comparison and concatenation operators Cypher provides special

pages/querying/differences-in-cypher-implementations.mdx

@@ -187,6 +187,7 @@ Such a construct is not supported in Memgraph, but you can use `collect()` [aggr
 
 {<h4 className="custom-header">Patterns in expressions</h4>}
 Patterns in expressions are supported in Memgraph in particular functions, like `exists(pattern)`.
+Memgraph also supports filtering based on patterns, like `MATCH (n) WHERE NOT (n)-->()`.
 In other cases, Memgraph does not yet support patterns in functions, e.g. `size((n)-->())`.
 Most of the time, the same functionalities can be expressed differently in Memgraph
 using `OPTIONAL` expansions, function calls, etc.