Add a limitation involving cascade deletions on a circular dependency #…

…19 (#21)

* Add a limitation involving cascade deletions on a circular dependency

* Refine the limitations description

* Fix --tables limitation

README.md

@@ -34,6 +34,10 @@ To solve the preceding issues, this tool works as follows.
 
 * This tool does not guarantee the atomicity of deletion. If you access the rows that are being deleted, you will get the inconsistent view of the database.
 * This tool does not delete rows which were inserted while the tool was running.
+* This tool does not support truncating tables that use foreign key constraints in some scenarios:
+  * If there is a circular dependency among the tables, truncation will be failed.
+  * If --tables is used for a table that is referenced by other tables with ON DELETE CASCADE, such tables will also be truncated.
+  * If `--exclude-tables` is used only for the referencing table that has ON DELETE CASCADE, that table will be truncated by cascade-deletion of the referenced table.
 
 ## Install