[Sqlalchemy-tickets] Issue #4037: Glitch in the custom DDL documentation (zzzeek/sqlalchemy)

[Lele G. <iss...@bi...>]

New issue 4037: Glitch in the custom DDL documentation
https://bitbucket.org/zzzeek/sqlalchemy/issues/4037/glitch-in-the-custom-ddl-documentation

Lele Gaifax:

In the `trigger` definition near line 62 of `doc/build/core/ddl.rst` (sorry, could not find the proper syntax to hyperlink that line), where it is explicitly showing an example for PostgreSQL, the `DDL` uses a syntax which is not valid for a PG trigger:
```
CREATE TRIGGER dt_ins BEFORE INSERT ON mytable
FOR EACH ROW BEGIN SET NEW.data='ins'; END
```

Accordingly to the [documentation](https://www.postgresql.org/docs/9.6/static/sql-createtrigger.html) a trigger cannot execute an arbitrary code block, but must run a *procedure*, so for example it could be written as:
```
CREATE TRIGGER dt_ins BEFORE INSERT ON mytable
FOR EACH ROW EXECUTE PROCEDURE set_data_field('ins');
```