As of version 0.8, SQLAlchemy can resolve the ambiguous join using only the foreign_keys keyword parameter to relationship. publish_user = relationship(User, foreign_keys=[publishing_user_id], backref=backref(‘pages’, order_by=id)) edit_user = relationship(User, foreign_keys=[last_edit_user_id]) Documentation at http://docs.sqlalchemy.org/en/rel_0_9/orm/join_conditions.html#handling-multiple-join-paths
This method assigns a 1 or 0 for null columns, and adds them all together. Hopefully you don’t have too many nullable columns to add up here… SELECT ((CASE WHEN col1 IS NULL THEN 1 ELSE 0 END) + (CASE WHEN col2 IS NULL THEN 1 ELSE 0 END) + (CASE WHEN col3 IS NULL … Read more
It was meant for readability. Before, SQL was written in plain-text editors (no syntax/code highlighting) and keywords needed to be differentiated for better readability and maintenance. SELECT column_name FROM table_name WHERE column_name = column_value vs select column_name from table_name where column_name = column_value See the difference? The first word in each line told the reader … Read more
Generally all modifications can cause a deadlock and selects will not (get to that later). So No you cannot ignore these. You can somewhat ignore select depending on your database and settings but the others will give you deadlocks. You don’t even need multiple tables. The best way to create a deadlock is to do … Read more
This syntax works for Oracle and PostgreSQL: SELECT * FROM table_name WHERE (key_part_1, key_part_2) IN ( (‘B’,1), (‘C’,2) );
Oracle 11g provides a PIVOT operation that does what you want. Oracle 11g solution select * from (select id, k, v from _kv) pivot(max(v) for k in (‘name’, ‘age’, ‘gender’, ‘status’) (Note: I do not have a copy of 11g to test this on so I have not verified its functionality) I obtained this solution … Read more
To get a count of the number of unique combinations of id, name and address: SELECT Count(*) FROM ( SELECT DISTINCT id , name , address FROM your_table ) As distinctified
Create a EXTERNAL_ID column, and use it to store the identifier from the external system. You should add an EXTERNAL_TYPE column and set that to ‘GOOGLE’.. when you go to integrate further authentication-providers, this can be set to different values (eg ‘OPEN_ID’, ‘FACEBOOK’.) When interfacing with external systems, it is always necessary to store the … Read more
Assuming there are not duplicate rows in AA and BB (i.e. all the same values), a full outer join is the equivalent of the union of a left join and a right join. SELECT * FROM AA LEFT JOIN BB ON AA.C_ID = BB.C_ID UNION SELECT * FROM AA RIGHT JOIN BB ON AA.C_ID = … Read more
columns have name and type attributes for c in columns: print c.name, c.type