$employee_attendance =
DB::Connection('sql_srv')
->table('CHECKINOUT')
->leftJoin('USERINFO', 'CHECKINOUT.USERID', '=', 'USERINFO.USERID')
->leftjoin(DB::Connection('mysql_srv'))
->table('EMPLOYEE', 'USERINFO.CardNo', '=', 'EMPLOYEE.CardID')
->get();
Hi, I had been searching for the solution in the internet for a long time but still I couldn't find the solution, most of the search results is joining on different tables in single database.
I need the solution for different DB::Connection left join and get the query results.
Moreover, all databases are within the same server, if using single connection like DB::connection('sql_srv') or ('mysq_srv') can get the result easily only when join is having issues.
Related
I'm trying to extract the data by joining the two table, in pyspark. My join Query looks like:
SELECT COUNT(DISTINCT m.ticker),to_date(m.date) FROM extractalpha_cam2 m LEFT OUTER JOIN TOP1000 u ON u.date = to_date(m.date) GROUP BY m.date ORDER BY m.date
It is throwing the error:
Error:Py4JJavaError: An error occurred while calling
z:org.apache.zeppelin.spark.ZeppelinContext.showDF
But when, i tried extracting the data from each table, it's working fine. My queries from single table are like
SELECT to_date(date) FROM extractalpha_cam2
SELECT date from TOP1000
These two queries working fine. Can anyone help me in extracting the data from both table by joining.
It would be really helpful if anyone can share any such link, which can guide me in writing the efficient queries in pyspark.
I checked and found that, this error comes when, the job you are running took more time than the time you set for timeout. In my case it was 300 seconds.
Let me know if anyone has more valuable answer than this. Thanks
I tried to attack this problem using the classical JOIN operation: I have a table Posts and a table Followings, so given a user_id I retrieve its followings and get the posts of those followings by joining both tables. Until here it's fine.
Since it's a timeline, I need to establish a number of posts retrieve, let's say 30. There will be a button to retrieve the previous 30 posts and so on, which means that I need to retrieve the timeline in chunks of 30 posts.
The problems comes when thinking about efficiency. I'm not an expert on DBs but I remember that on MySQL you can do something like this (I don't know how it's in PostgreSQL though):
SELECT * FROM [... join ...] LIMIT 0,30
SELECT * FROM [... join ...] LIMIT 30,60
SELECT * FROM [... join ...] LIMIT 60,90
I guess that internally it's performing the join operation, consequently obtaining all rows to later retrieve a limited number of rows. The problem is that in this example it is repeating the same join operation 3 times and I was wondering if there is a way to force the database to store in a cache that join result so that the join operation is only performed once and then the result is limited afterwards, or, on the other hand, I would like to know if there is no way I can avoid performing joins all the time in each query.
Edit: I'm interested in a PostgreSQL solution.
Thanks.
I have a custom query along these lines. I get the list of orderIds from outside. I have the entire order object list with me, so I can change the query in any way, if needed.
#Query("SELECT p FROM Person p INNER JOIN p.orders o WHERE o.orderId in :orderIds)")
public List<Person> findByOrderIds(#Param("orderIds") List<String> orderIds);
This query works fine, but sometimes it may have anywhere between 50-1000 entries in the orderIds list sent from outside function. So it becomes very slow, taking as much as 5-6 seconds which is not fast enough. My question is, is there a better, faster way to do this? When I googled, and on this site, I see we can use ANY, EXISTS: Postgresql: alternative to WHERE IN respective WHERE NOT IN or create a temporary table: https://dba.stackexchange.com/questions/12607/ways-to-speed-up-in-queries-under-postgresql or join this to VALUES clause: Alternative when IN clause is inputed A LOT of values (postgreSQL). All these answers are tailored towards direct SQL calls, nothing based on JPA. ANY keyword is not supported by spring-data. Not sure about creating temporary tables in custom queries. I think I can do it with native queries, but have not tried it. I am using spring-data + OpenJPA + PostgresSQL.
Can you please suggest a solution or give pointers? I apologize if I missed anything.
thanks,
Alice
You can use WHERE EXISTS instead of IN Clause in a native SQL Query as well as in HQL in JPA which results in a lot of performance benefits. Please see sample below
Sample JPA Query:
SELECT emp FROM Employee emp JOIN emp.projects p where NOT EXISTS (SELECT project from Project project where p = project AND project.status <> 'Active')
I'm using Zend Framework for my website and I'd like to retrieve some data from my PostgreSQL database.
I have a request like :
SELECT DISTINCT ON(e.id) e.*, f.*, g.* FROM e, f, g
WHERE e.id = f.id_e AND f.id = g.id_f
This request works well but I don't know how to convert the DISTINCT ON(e.id) with Zend.
It seems that I can get DISTINCT rows but no distinct columns.
$select->distinct()->from("e")->join("f", "e.id = f.id_e")
->join("g", "f.id = g.id_f");
Any idea on how to make a select with distinct column ?
Thanks for help
You probably can't do this with Zend Framework since distinct on is not part of the SQL standard (end of page in Postgres documentation). Although Postgres supports it, I would assume its not part of Zend Framework because you could in theory configure another database connection which does not offer support.
If you know in advance that you're developing for a specific database (Postgres in this case), you could use manually written statements instead. You'll gain more flexibility within the queries and better performance at the cost of no longer being able to switch databases.
You would then instantiate a Zend_Db_Apdapter for Postgres. There a various methods available to get results for SQL queries which are described in the frameworks documentation starting at section Reading Query Results. If you choose to go this route I'd recommend to create an own subclass of the Zend_Db_Adapter_Pgsql class. This is to be able to convert data types and throw exceptions in case of errors instead of returning ambiguous null values and hiding error causes.
I usually use ORM instead of SQL and I am slightly out of touch on the different JOINs...
SELECT `order_invoice`.*
, `client`.*
, `order_product`.*
, SUM(product.cost) as net
FROM `order_invoice`
LEFT JOIN `client`
ON order_invoice.client_id = client.client_id
LEFT JOIN `order_product`
ON order_invoice.invoice_id = order_product.invoice_id
LEFT JOIN `product`
ON order_product.product_id = product.product_id
WHERE (order_invoice.date_created >= '2009-01-01')
AND (order_invoice.date_created <= '2009-02-01')
GROUP BY `order_invoice`.`invoice_id`
The tables/ columns are logically names... it's an shop type application... the query works... it's just very very slow...
I use the Zend Framework and would usually use Zend_Db_Table_Row::find(Parent|Dependent)Row(set)('TableClass') but I have to make lots of joins and I thought it'll improve performance by doing it all in one query instead of hundreds...
Can I improve the above query by using more appropriate JOINs or a different implementation? Many thanks.
The query is wrong, the GROUP BY is wrong. All columns in the SELECT-part that are not in an aggregate function, have to be in the GROUP BY. You mention only one column.
Change the SQL Mode, set it to ONLY_FULL_GROUP_BY.
When this is done and you have a correct query, use EXPLAIN to find out how the query is executed and what indexes are used. Then start optimizing.