Ability to add descending order indexes (#262)

* DescIndex(column) for descending index columns, refs #260
* Ability to add desc indexes using CLI, closes #260

sqlite_utils/cli.py

@@ -5,7 +5,7 @@ from datetime import datetime
 import hashlib
 import pathlib
 import sqlite_utils
-from sqlite_utils.db import AlterError
+from sqlite_utils.db import AlterError, DescIndex
 import textwrap
 import io
 import itertools
@@ -450,11 +450,21 @@ def index_foreign_keys(path, load_extension):
 )
 @load_extension_option
 def create_index(path, table, column, name, unique, if_not_exists, load_extension):
-    "Add an index to the specified table covering the specified columns"
+    """
+    Add an index to the specified table covering the specified columns.
+    Use "sqlite-utils create-index mydb -- -column" to specify descending
+    order for a column.
+    """
     db = sqlite_utils.Database(path)
     _load_extensions(db, load_extension)
+    # Treat -prefix as descending for columns
+    columns = []
+    for col in column:
+        if col.startswith("-"):
+            col = DescIndex(col[1:])
+        columns.append(col)
     db[table].create_index(
-        column, index_name=name, unique=unique, if_not_exists=if_not_exists
+        columns, index_name=name, unique=unique, if_not_exists=if_not_exists
     )
 
 

sqlite_utils/db.py

@@ -144,6 +144,10 @@ class InvalidColumns(Exception):
     pass
 
 
+class DescIndex(str):
+    pass
+
+
 _COUNTS_TABLE_CREATE_SQL = """
 CREATE TABLE IF NOT EXISTS [{}](
    [table] TEXT PRIMARY KEY,
@@ -1156,6 +1160,13 @@ class Table(Queryable):
             index_name = "idx_{}_{}".format(
                 self.name.replace(" ", "_"), "_".join(columns)
             )
+        columns_sql = []
+        for column in columns:
+            if isinstance(column, DescIndex):
+                fmt = "[{}] desc"
+            else:
+                fmt = "[{}]"
+            columns_sql.append(fmt.format(column))
         sql = (
             textwrap.dedent(
                 """
@@ -1167,7 +1178,7 @@ class Table(Queryable):
             .format(
                 index_name=index_name,
                 table_name=self.name,
-                columns=", ".join("[{}]".format(c) for c in columns),
+                columns=", ".join(columns_sql),
                 unique="UNIQUE " if unique else "",
                 if_not_exists="IF NOT EXISTS " if if_not_exists else "",
             )