I'm looking for a way to run a nested correlated query that requires a CTE created above the script. For example if I had:
with first_cte as (
select *
from a_table
where 1=1
)
select * from
(select
column_1,
column_2,
column_3
from b_table b
inner join first_cte f on f.user_id = b.user_id
where 1=1) x
If I just wanted to test the nested query, it will say that first_cte doesn't exist. Is there a way to highlight the CTE so that it will run when I'm testing nested queries?
I'm using PostgreSQL btw. Thanks!!!
There are Execute selection and Execution options features in DataGrip.
Related
I am trying to add component 'tNetezzainput' in Talend
with query like
select col1,col2 from
(select col1,col2 from tab2 )
when i run sub query independently it is allowing to get schema
but when i run above query it is showing error like
org.netezza.error.NzSQLexception:ERROR
(above query)
You need to add an alias after the parentheses (I randomly chose ‘x’):
select col1,col2 from
(select col1,col2 from tab2 ) x
Suppose I have a query which says
Select * from (
select coalesce(mytable.created_date,mytable1.created_date) as created_date,...
from mytable
left join mytable1 ON (mytable.id=mytable1.id)
--Other Joins and tables here
) as foo
where created_date > CURRENT_DATE
Will Postgres select only the rows where created_date is > CURRENT_DATE for inner query joins where I am joining many tables?
Or will it take all rows from mytable and make joins with other tables on inner query, then check for created_date > CURRENT_DATE.
Is my previous query the same as
select coalesce(mytable.created_date,mytable1.created_date),... from mytable
left join mytable1 ON (mytable.id=mytable1.id)
--Other Joins and tables here
WHERE
coalesce(mytable.created_date,mytable1.created_date) > CURRENT_DATE
As you can see when you use EXPLAIN, the optimizer can “flatten” such subqueries, so that the execution plans for these two queries will be the same.
In other words, the optimizer is able to push the WHERE condition into the subquery and the join, so that it can be executed first.
Moreover, if created_date happens to be a column of mytable1, PostgreSQL will deduce that created_date can never be NULL and perform an inner join rather than an outer join.
Example for correlated subquery given in a book is as follows;
Customers who placed orders on February 12, 2007
SELECT custid, companyname
FROM Sales.Customers AS C
WHERE EXISTS
(SELECT *
FROM Sales.Orders AS O
WHERE O.custid = C.custid
AND O.orderdate = '20070212');
But, I wrote following code for the same purpose using simple subquery
SELECT custid, companyname
FROM Sales.Customers
WHERE custid IN
(SELECT [custid] FROM [Sales].[Orders]
WHERE [orderdate] ='20070212')
Both gives identical output. Which method is better? and why? and I do not understand the use of EXISTS here in the first set of codes
I tried similar queries on my own data on SQL Server 2016 SP!:
select
*
from EXT.dbo_CUSTTABLE
where ACCOUNTNUM in
(select CUSTACCOUNT from EXT.dbo_SALESLINE b
where b.CREATEDDATETIME between '20170101 00:00' and '20170102 23:59');
select
*
from EXT.dbo_CUSTTABLE a
where exists
(select * from EXT.dbo_SALESLINE b
where a.ACCOUNTNUM=b.CUSTACCOUNT
and b.CREATEDDATETIME between '20170101 00:00' and '20170102 23:59');
Look at the execution plans, they are identical!
If I add a clustered index on the customer table, and an index on the salesline, we get a more efficient query, with index seek and inner join, in stead of table scans and hash joins, but still identical!:
Now if you are using another version of SQL server youre results may vary, since the query optimizer changes between versions.
Take this query:
SELECT c.CustomerID, c.AccountNumber, COUNT(*) AS CountOfOrders,
SUM(s.TotalDue) AS SumOfTotalDue
FROM Sales.Customer AS c
INNER JOIN Sales.SalesOrderheader AS s ON c.CustomerID = s.CustomerID
GROUP BY c.CustomerID, c.AccountNumber
ORDER BY c.CustomerID;
I expected COUNT(*) to count the rows in Sales.Customer but to my surprise it counts the number of rows in the joined table.
Any idea why this is? Also, is there a way to be explicit in specifying which table COUNT() should operate on?
Query Processing Order...
The FROM clause is processed before the SELECT clause -- which is to say -- by the time SELECT comes into play, there is only one (virtual) table it is selecting from -- namely, the individual tables after their joined (JOIN), filtered (WHERE), etc.
If you just want to count over the one table, then you might try a couple of things...
COUNT(DISTINCT table1.id)
Or turn the table you want to count into a sub-query with count() inside of it
Is there a way to combine two SQL queries into a single SELECT query in PostgreSQL?
My requirements are as follows:
SELECT id FROM table1;
SELECT name FROM table2 WHERE table2.id = table1.id;
I think I need to pass values of table1.id in as some sort of dynamic values (loop values) for use in the SELECT statement executed on table2. What is the easiest way to solve this problem, is it possible to do this with stored procedures or functions in PostgreSQL?
select t1.id, name
from
table1 t1
inner join
table2 t2 using (id)
where t1.id = 1