I should add, please specify which backend you're using and what DDL sequence you are looking to emit.
On Tue, Nov 6, 2018 at 3:21 PM Mike Bayer <mike...@zzzcomputing.com> wrote: > > On Tue, Nov 6, 2018 at 2:54 PM <ly...@mode.net> wrote: > > > > Hi, > > > > I find that `UniqueConstraint` from `sqlachemy` and > > `op.create_unique_constraint` by `alembic`, it cannot handle multiple > > columns that contain null values. > > > > I saw we can solve using SQL commands via some tricky ways like creating > > unique index and coalesce, do we have some ways using `sqlachemy` instead > > of directly using `SQL` to solve this issue? > > > the UniqueConstraint object spits out "CREATE UNIQUE CONSTRAINT" or > equivalent DDL only. The "null values" issue is very different > across backends - in particular, the limitation that NULL values > aren't allowed is a peculiarity specific to Microsoft SQL Server. > > Given that, there are ways to create DDL that does what you need, and > then if necessary, to have different kinds of DDL emit based on > different backends if you are looking for cross-database > compatibility. For intricate edge cases like this, it's much better > that SQLAlchemy gives the developer the tools to create exactly the > DDL sequence that is tailored towards their needs, rather than it > trying to pre-package a particular solution that probably won't work > the same way across different backends or otherwise be flexible > enough. > > > > > > Thanks! > > > > Lydia > > > > -- > > SQLAlchemy - > > The Python SQL Toolkit and Object Relational Mapper > > > > http://www.sqlalchemy.org/ > > > > To post example code, please provide an MCVE: Minimal, Complete, and > > Verifiable Example. See http://stackoverflow.com/help/mcve for a full > > description. > > --- > > You received this message because you are subscribed to the Google Groups > > "sqlalchemy" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to sqlalchemy+unsubscr...@googlegroups.com. > > To post to this group, send email to sqlalchemy@googlegroups.com. > > Visit this group at https://groups.google.com/group/sqlalchemy. > > For more options, visit https://groups.google.com/d/optout. -- SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper http://www.sqlalchemy.org/ To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example. See http://stackoverflow.com/help/mcve for a full description. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at https://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
