Add References Target Primary Key By Default as a Postgres TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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@@ -912,6 +912,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Prevent A Query From Running Too Long](postgres/prevent-a-query-from-running-too-long.md)
 - [Print The Query Buffer In psql](postgres/print-the-query-buffer-in-psql.md)
 - [Put Unique Constraint On Generated Column](postgres/put-unique-constraint-on-generated-column.md)
+- [References Target Primary Key By Default](postgres/references-target-primary-key-by-default.md)
 - [Remove Not Null Constraint From A Column](postgres/remove-not-null-constraint-from-a-column.md)
 - [Renaming A Sequence](postgres/renaming-a-sequence.md)
 - [Renaming A Table](postgres/renaming-a-table.md)

postgres/references-target-primary-key-by-default.md

@@ -0,0 +1,37 @@
+# References Target Primary Key By Default
+
+Typically when I am creating a table or adding a column that involves a foreign
+key constraint, I explicitly name the reference column.
+
+```sql
+create table contacts (
+  id int generated always as identity primary key,
+  user_id int references users(id);
+);
+```
+
+The [Create Table PostgreSQL
+Docs](https://www.postgresql.org/docs/17/sql-createtable.html) point out that
+specifying the reference column isn't strictly necessary.
+
+> These clauses specify a foreign key constraint, which requires that a group
+> of one or more columns of the new table must only contain values that match
+> values in the referenced column(s) of some row of the referenced table. If
+> the refcolumn list is omitted, the primary key of the reftable is used.
+
+If we're using the primary key as the reference column, then we can choose to
+omit the reference column.
+
+```sql
+create table contacts (
+  id int generated always as identity primary key,
+  user_id int references users;
+);
+```
+
+In the same way we can do this when adding a column.
+
+```sql
+alter table contacts
+  add column account_id int references account;
+```