Document new constraint type in create_constraint: primary_key (#839)

Author: kvch

docs/operations/create_constraint.mdx

@@ -5,7 +5,7 @@ description: A create constraint operation adds a new constraint to an existing
 
 ## Structure
 
-`UNIQUE`, `CHECK` and `FOREIGN KEY` constraints are supported.
+`UNIQUE`, `CHECK`, `PRIMARY KEY` and `FOREIGN KEY` constraints are supported.
 
 Required fields: `name`, `table`, `type`, `up`, `down`.
 
@@ -15,7 +15,7 @@ create_constraint:
   table: name of table
   name: my_unique_constraint
   columns: [column1, column2]
-  type: unique | check | foreign_key
+  type: unique | check | primary_key | foreign_key
   check: SQL expression for CHECK constraint
   no_inherit: true|false
   references:
@@ -103,6 +103,15 @@ Add a check constraint on the `sellers_name` and `sellers_zip` fields on the `ti
 
 <ExampleSnippet example="45_add_table_check_constraint.yaml" languange="yaml" />
 
+### Add a `PRIMARY KEY` constraint
+
+Add a primary key constraint to the the `tasks` table:
+
+<ExampleSnippet
+  example="55_add_primary_key_constraint_to_table.yaml"
+  languange="yaml"
+/>
+
 ### Add a `FOREIGN KEY` constraint
 
 Add a multi-column foreign key constraint to the the `tickets` table. The `up` SQL expressions here don't do any data transformation:

examples/.ledger

@@ -52,3 +52,4 @@
 52_create_table_with_exclusion_constraint.yaml
 53_add_column_with_volatile_default.yaml
 54_create_index_with_opclass.yaml
+55_add_primary_key_constraint_to_table.yaml

examples/55_add_primary_key_constraint_to_table.yaml

@@ -0,0 +1,22 @@
+operations:
+  - create_table:
+      name: tasks
+      columns:
+        - name: id
+          type: serial
+        - name: title
+          type: varchar(255)
+          nullable: false
+        - name: description
+          type: varchar(255)
+        - name: deadline
+          type: time with time zone
+  - create_constraint:
+      name: tasks_pkey
+      table: tasks
+      columns: [id]
+      type: primary_key
+      up:
+        id: id
+      down:
+        id: id