Use a synthetic primary key.

robot-server/robot_server/persistence/_tables/schema_3.py

@@ -125,6 +125,7 @@
 run_command_table = sqlalchemy.Table(
     "run_command",
     metadata,
+    sqlalchemy.Column("row_id", sqlalchemy.Integer, primary_key=True),
     sqlalchemy.Column(
         "run_id", sqlalchemy.String, sqlalchemy.ForeignKey("run.id"), nullable=False
     ),
@@ -137,7 +138,12 @@
         sqlalchemy.PickleType(pickler=legacy_pickle, protocol=PICKLE_PROTOCOL_VERSION),
         nullable=False,
     ),
-    sqlalchemy.PrimaryKeyConstraint("run_id", "command_id"),
+    sqlalchemy.Index(
+        "ix_run_run_id_command_id",  # An arbitrary name for the index.
+        "run_id",
+        "command_id",
+        unique=True,
+    ),
     sqlalchemy.Index(
         "ix_run_run_id_index_in_run",  # An arbitrary name for the index.
         "run_id",

robot-server/tests/persistence/test_tables.py

@@ -79,15 +79,19 @@
     """,
     """
     CREATE TABLE run_command (
+        row_id INTEGER NOT NULL,
         run_id VARCHAR NOT NULL,
         index_in_run INTEGER NOT NULL,
         command_id VARCHAR NOT NULL,
         command BLOB NOT NULL,
-        PRIMARY KEY (run_id, command_id),
+        PRIMARY KEY (row_id),
         FOREIGN KEY(run_id) REFERENCES run (id)
     )
     """,
     """
+    CREATE UNIQUE INDEX ix_run_run_id_command_id ON run_command (run_id, command_id)
+    """,
+    """
     CREATE UNIQUE INDEX ix_run_run_id_index_in_run ON run_command (run_id, index_in_run)
     """,
 ]
@@ -198,4 +202,7 @@ def record_statement(
     normalized_actual = [_normalize_statement(s) for s in actual_statements]
     normalized_expected = [_normalize_statement(s) for s in expected_statements]
 
-    assert normalized_actual == normalized_expected
+    # Compare ignoring order. SQLAlchemy appears to emit CREATE INDEX statements in a
+    # nondeterministic order that varies across runs. Although statement order
+    # theoretically matters, it's unlikely to matter in practice for our purposes here.
+    assert set(normalized_actual) == set(normalized_expected)