Add Remove Not Null Constraint From A Column as a postgres til

README.md

@@ -9,7 +9,7 @@ and pairing with smart people at Hashrocket.
 
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-_920 TILs and counting..._
+_921 TILs and counting..._
 
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@@ -490,6 +490,7 @@ _920 TILs and counting..._
 - [Pretty Printing JSONB Rows](postgres/pretty-printing-jsonb-rows.md)
 - [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)
+- [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)
 - [Restart A Sequence](postgres/restart-a-sequence.md)

postgres/remove-not-null-constraint-from-a-column.md

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+# Remove Not Null Constraint From A Column
+
+When you want to add a [`not
+null`](https://www.postgresql.org/docs/current/ddl-constraints.html#id-1.5.4.6.6)
+constraint to a column, you do so by _setting_ it.
+
+```sql
+alter table books
+  alter column publication_date
+  set not null;
+```
+
+You can remove a `not null` constraint from a column, by _dropping_ it.
+
+```sql
+alter table books
+  alter column publication_date
+  drop not null;
+```
+
+Notice this excerpt of syntax from the official Postgres docs:
+
+```
+... ALTER [ COLUMN ] column_name { SET | DROP } NOT NULL
+```
+
+[source](https://www.postgresql.org/docs/current/sql-altertable.html)