SQL : select the oldest record for each distinct element
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sql query to get latest record for all distinct items in a table
I apologize for the poor worded title, let me illustrate first
Here is the table :
select task_id, task_status, date_change, username from logs order by task_id, date_change
TASK_ID TASK_STATUS DATE_CHANGE USERNAME 1 101 Green 2019/01/03 Camille 2 101 Blue 2019/01/07 Lucas 3 101 Green 2019/01/09 Rudy 4 102 Blue 2019/01/03 Lucas 5 102 Green 2019/01/04 Delphine 6 103 Yellow 2019/01/07 Penelope 7 103 Green 2019/01/11 Rudy 8 103 Blue 2019/01/14 Delphine 9 103 Green 2019/01/18 Camille 10 104 Blue 2019/01/08 Rudy 11 104 Green 2019/01/10 Camille 12 104 Green 2019/01/14 Penelope
I have several tasks, each of which can have a different status. For every tasks, I want to extract the row with the earliest green status.
So in this case the result would be :
TASK_ID TASK_STATUS DATE_CHANGE USERNAME 1 101 Green 2019/01/03 Camille 2 102 Green 2019/01/04 Delphine 3 103 Green 2019/01/11 Rudy 4 104 Green 2019/01/10 Camille
Here is the closest i've got to a solution :
select task_id, task_status, date_change, username from logs where task_status =('Green') and task_id = ('101') and date_change = ( select min(date_change) from logs where task_status = ('Green') and task_id =('101') )
It is not good at all, I have to do a query for every single task, totally unpractical.
Is there a way to use a kind of variable and change the last line by something like :
and date_change = ( select min(date_change) from logs where task_status = ('Green') and task_id =($CURRENT_TASK_ID) )
Or maybe another way altogether to solve that problem ?
I greatly thank you for you time.
select * from logs l where Date_Change = ( select min(DATE_CHANGE) from logs li where li.task_id = l.task_id and li.task_Status = l.task_status ) and TASK_STATUS = 'Green';
Finding the Oldest/Youngest Records Within a Group, How to find the oldest or most recent record associated with a particular foreign key. This is straightforward in SQL. per holding ( holding_id and holding_type together ensure a unique StockHolding or BondHolding ). A common query that crops up in web apps is finding the oldest or the most recent record in a single table. This is straightforward in SQL. You can even write the relevant part of the query without knowing anything about the table (other than the fact that it has a timestamp column called created_at):
You only need to
group by task_id and get the minimum date_change:
select task_id, 'Green' task_status, min(date_change) date_change from logs where task_status = 'Green' group by task_id
For a specific
task_id = '101' you don't need the grouping:
select '101' task_id, 'Green' task_status, min(date_change) date_change from logs where task_status = 'Green' and task_id = '101'
SQL DISTINCT and TOP in Same Query, How do the SQL Distinct and SQL TOP SELECT modifiers Work Together in the same All the examples for this lesson are based on Microsoft SQL Server So, in this case, the statement will return distinct rows for FirstName and LastName. SQL HOME SQL Intro SQL Syntax SQL Select SQL Select Distinct SQL Where SQL And, Or, Not SQL Order By SQL Insert Into SQL Null Values SQL Update SQL Delete SQL Select Top SQL Min and Max SQL Count, Avg, Sum SQL Like SQL Wildcards SQL In SQL Between SQL Aliases SQL Joins SQL Inner Join SQL Left Join SQL Right Join SQL Full Join SQL Self Join SQL
In Oracle, this can be achieved very efficiently using analytic functions, aka window functions. For this use case,
ROW_NUMBER() is your friend :
SELECT * FROM ( SELECT l.*, ROW_NUMBER() OVER(PARTITION BY task_id ORDER BY date_change) rn FROM logs l WHERE ASK_STATUS = 'Green' ) x WHERE rn = 1
The inner query assigns a number to each record in groups having the same
task_status, with the earliest record having number
1. You can run the subquery to see the results. Then, the outer query filters in the first record in each group.
Window functions are available in Oracle since early versions (8i). They usually beat aggregation and subqueries in terms of efficiency.
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SQL, Top-N Analysis in SQL deals with How to limit the number of rows returned from Input : SELECT ROWNUM as RANK, first_name, last_name, employee_id, salary the required fields are displayed for those 3 employees who were hired earliest. analytic function assigns a sequential rank to each distinct value in output. SQL HOME SQL Intro SQL Syntax SQL Select SQL Select Distinct SQL Where SQL And, Or, Not SQL Order By SQL Insert Into SQL Null Values SQL Update SQL Delete SQL Select Top SQL Min and Max SQL Count, Avg, Sum SQL Like SQL Wildcards SQL In SQL Between SQL Aliases SQL Joins SQL Inner Join SQL Left Join SQL Right Join SQL Full Join SQL Self Join SQL
- You may have a look at this similar question: stackoverflow.com/questions/18725168/…
- You did exactly what I asked, and taught me a very interesting use of aliases. You have all my thanks !
- Thank you very much for your feedback ! Your solution worked very well, but I'm not sure how to apply it when a column that doesn't perfectly group is added (see my edited post), is there something to be done ? Again, thank you