This is exactly what select_related() does. The only gotcha is that you have to start with the Answer model, rather than Question, but the result is the same: answers = Answer.objects.filter(question_id=1).select_related() Now each answer object has a pre-fetched ‘question’ attribute, and accessing it won’t hit the db again.
Use: SELECT t.*, x.combinedsolutions FROM TICKETS t LEFT JOIN (SELECT s.ticket_id, GROUP_CONCAT(s.soution) AS combinedsolutions FROM SOLUTIONS s GROUP BY s.ticket_id) x ON x.ticket_id = t.ticket_id Alternate: SELECT t.*, (SELECT GROUP_CONCAT(s.soution) FROM SOLUTIONS s WHERE s.ticket_id = t.ticket_id) AS combinedsolutions FROM TICKETS t
When you have related tables you often have one-to-many or many-to-many relationships. So when you join to TableB each record in TableA many have multiple records in TableB. This is normal and expected. Now at times you only need certain columns and those are all the same for all the records, then you would need … Read more
I think your last statement is the best way. You can also try SELECT A.* from A left join B on A.x = B.y where B.y is null
This happens because Spark tries to do Broadcast Hash Join and one of the DataFrames is very large, so sending it consumes much time. You can: Set higher spark.sql.broadcastTimeout to increase timeout – spark.conf.set(“spark.sql.broadcastTimeout”, newValueForExample36000) persist() both DataFrames, then Spark will use Shuffle Join – reference from here PySpark In PySpark, you can set the … Read more
SELECT t.* FROM unnest(ARRAY[1,2,3,2,3,5]) item_id LEFT JOIN items t on t.id=item_id The above query select items from items table with ids: 1,2,3,2,3,5 in that order.
In MySQL writing JOIN unqualified implies INNER JOIN. In other words the INNER in INNER JOIN is optional. INNER and CROSS are synonyms in MySQL. For clarity I write JOIN or INNER JOIN if I have a join condition and CROSS JOIN if I don’t have a condition. The allowed syntax for joins is described … Read more
It seems the answer to your question is no, however one hack you can use is to assign a dummy column to separate each new table. This works especially well if you’re looping through a result set for a list of columns in a scripting language such as Python or PHP. SELECT ” as table1_dummy, … Read more
That is because null on either side of the addition operator will yield a result of null. You can use ISNULL(LiabilityPremium, 0) Example: ISNULL(l.LiabilityPremium,0) + ISNULL(h.LiabilityPremium,0) as LiabilityPremium or you can use COALESCE instead of ISNULL. COALESCE(l.LiabilityPremium,0) + COALESCE(h.LiabilityPremium,0) as LiabilityPremium Edit I am not sure if this is coincidence with this small data set … Read more