Ability to create unique indexes, refs #14

docs/python-api.rst

@@ -388,6 +388,13 @@ By default the index will be named ``idx_{table-name}_{columns}`` - if you want
         index_name="good_dogs_by_age"
     )
 
+You can create a unique index by passing ``unique=True``::
+
+.. code-block:: python
+
+    dogs.create_index(["name"], unique=True)
+
+
 Vacuum
 ======
 

sqlite_utils/db.py

@@ -236,16 +236,19 @@ class Table:
         self.exists = True
         return self
 
-    def create_index(self, columns, index_name=None):
+    def create_index(self, columns, index_name=None, unique=False):
         if index_name is None:
             index_name = "idx_{}_{}".format(
                 self.name.replace(" ", "_"), "_".join(columns)
             )
         sql = """
-            CREATE INDEX {index_name}
+            CREATE {unique}INDEX {index_name}
                 ON {table_name} ({columns});
         """.format(
-            index_name=index_name, table_name=self.name, columns=", ".join(columns)
+            index_name=index_name,
+            table_name=self.name,
+            columns=", ".join(columns),
+            unique="UNIQUE " if unique else "",
         )
         self.db.conn.execute(sql)
         return self

tests/test_create.py

@@ -170,6 +170,24 @@ def test_create_index(fresh_db, columns, index_name, expected_index):
     assert expected_index == dogs.indexes[0]
 
 
+def test_create_index_unique(fresh_db):
+    dogs = fresh_db["dogs"]
+    dogs.insert({"name": "Cleo", "twitter": "cleopaws", "age": 3, "is_good_dog": True})
+    assert [] == dogs.indexes
+    dogs.create_index(["name"], unique=True)
+    assert (
+        Index(
+            seq=0,
+            name="idx_dogs_name",
+            unique=1,
+            origin="c",
+            partial=0,
+            columns=["name"],
+        )
+        == dogs.indexes[0]
+    )
+
+
 @pytest.mark.parametrize(
     "data_structure",
     (