Add ENFORCED documentation (#794)

doc-surrealdb_versioned_docs/version-latest/surrealql/statements/define/table.mdx

@@ -21,7 +21,7 @@ The `DEFINE TABLE` statement allows you to declare your table by name, enabling
 DEFINE TABLE [ OVERWRITE | IF NOT EXISTS ] @name
 	[ DROP ]
 	[ SCHEMAFULL | SCHEMALESS ]
-	[ TYPE [ ANY | NORMAL | RELATION [ IN | FROM ] @table [ OUT | TO ] @table ] ]
+	[ TYPE [ ANY | NORMAL | RELATION [ IN | FROM ] @table [ OUT | TO ] @table ] [ ENFORCED ] ]
 	[ AS SELECT @projections
 		FROM @tables
 		[ WHERE @condition ]
@@ -384,3 +384,73 @@ DEFINE TABLE assigned_to SCHEMAFULL TYPE RELATION IN tag OUT sticky
         FOR create, select, update, delete
             WHERE in.owner == $auth.id AND out.author == $auth.id;
 ```
+
+## Using ENFORCED to ensure that related records exist
+
+<Since v="v2.0.0" />
+
+As relations are represented by standalone tables, they can be constructed before any linked records exist.
+
+```surql
+RELATE city:one->road_to->city:two SET 
+    distance = 12.4,
+    slope = 5.4;
+```
+
+```bash title="Output"
+[
+	{
+		distance: 12.4f,
+		id: road_to:pacwucj25a056hhs2s5h,
+		in: city:one,
+		out: city:two,
+		slope: 5.4f
+	}
+]
+```
+
+As such, a query on the relation will return nothing until the records it has been defined upon are created.
+
+```surql
+SELECT ->road_to->city FROM city;
+
+CREATE city:one, city:two;
+SELECT ->road_to->city FROM city;
+```
+
+```bash title="Output"
+-------- Query --------
+
+[]
+
+-------- Query --------
+
+[
+	{
+		"->road_to": {
+			"->city": [
+				city:two
+			]
+		}
+	},
+	{
+		"->road_to": {
+			"->city": []
+		}
+	}
+]
+```
+
+If this behaviour is not desirable, the `ENFORCED` clause can be used on a table of `TYPE RELATION` to disallow a `RELATE` statement from working unless it points to existing data.
+
+```surql
+DEFINE TABLE road_to TYPE RELATION IN city OUT city ENFORCED;
+
+RELATE city:one->road_to->city:three SET 
+    distance = 5.5,
+    slope = 30.0;
+```
+
+```bash title="Output"
+"The record 'city:three' does not exist"
+```