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Michael Bayer ha scritto:
> [...]
> from sqlalchemy import schema, types, sql, create_engine
>
> metadata = schema.MetaData()
> test = schema.Table(
> 'test', metadata,
> schema.Column('x', types.Integer, primary_key=True)
> )
>
> engine = create_engine('sqlite://')
>
> subquery = sql.exists(test.select().as_scalar())
> clause = sql.case([(True, subquery.select().as_scalar)])
> query = clause.select()
>
> engine.execute(query)
>
>> its more SQLA not warning you about an argument it doesn't like and then
>> it leading into problems. it should raise an error earlier. basically
>> exists() is like a select() and accepts the list of column expressions as
>> a list. if you were to pass your select inside of a [], you'd get a
>> valid SQL expression, though with two levels of "select".
>> sql.exists([test]) or exists().select_from(test) would be more effective.
>
Ok, thanks.
However, now I'm not sure to understand the example here:
http://www.sqlalchemy.org/docs/reference/sqlalchemy/expressions.html?highlight=exists#sqlalchemy.sql.expression.exists
# use on an existing select()
s = select([table.c.col1]).where(table.c.col2==5)
s = exists(s)
Regards Manlio
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