Add Max Identifier Length Is 63 Bytes as a postgres til.

README.md

@@ -132,6 +132,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [List All Columns Of A Specific Type](postgres/list-all-columns-of-a-specific-type.md)
 - [List All Versions Of A Function](postgres/list-all-versions-of-a-function.md)
 - [List Database Users](postgres/list-database-users.md)
+- [Max Identifier Length Is 63 Bytes](postgres/max-identifier-length-is-63-bytes.md)
 - [Restart A Sequence](postgres/restart-a-sequence.md)
 - [Send A Command To psql](postgres/send-a-command-to-psql.md)
 - [Special Math Operators](postgres/special-math-operators.md)

postgres/max-identifier-length-is-63-bytes.md

@@ -0,0 +1,26 @@
+# Max Identifier Length Is 63 Bytes
+
+In PostgreSQL, identifiers -- table names, column names, constraint names,
+etc. -- are limited to a maximum length of 63 bytes. Identifiers longer than
+63 characters can be used, but they will be truncated to the allowed length
+of 63.
+
+```sql
+> alter table articles
+    add constraint this_constraint_is_going_to_be_longer_than_sixty_three_characters_id_idx
+    check (char_length(title) > 0);
+NOTICE:  identifier "this_constraint_is_going_to_be_longer_than_sixty_three_characters_id_idx" will be truncated to "this_constraint_is_going_to_be_longer_than_sixty_three_characte"
+ALTER TABLE
+```
+
+Postgres warns us of identifiers longer than 63 characters, informing us of
+what it will be truncated to. It then proceeds to create the identifier.
+
+If postgres is trying to generate an identifier for us - say, for a foreign
+key constraint - and that identifier is longer than 63 characters, postgres
+will truncate the identifier somewhere in the middle so as to maintain the
+convention of terminating with, for example, `_fkey`.
+
+The 63 byte limit is not arbitrary. It comes from `NAMEDATALEN - 1`. By default
+`NAMEDATALEN` is 64. If need be, this value can be modified in the Postgres
+source. Yay, open-source database implementations.