Is there a better way (more efficient) to write this piece of code?
It works but it looks cluttered and could do with some cleanup.
It basically takes a column from different table and joins it with another, then it checks the last entry and takes the relevant event value. Finally it joins another script where there is no event found for that ID and joins that with the previous script.
I'm sure there's a cleaner way to write this script.
SELECT tA.[No_], tA.[Description], tA.[Source], tA.[VGroup], tB.[Event]
FROM [Table1] tA
LEFT JOIN [Table2] tB ON tA.[No_] = tB.[No]
WHERE NOT EXISTS (
SELECT NULL
FROM [Table2] tB
WHERE tB.[No] = tA.[No_]
)
UNION
SELECT tA.[No_], tA.[Description], tA.[Source], tA.[VGroup], tB.[Event]
FROM [Table1] tA
LEFT JOIN [Table2] tB ON tA.[No_] = tB.[No]
WHERE ID IN (
SELECT MAX(ID)
FROM [Table2]
GROUP BY [No]
)
It appears (although it's rather unclear), that you just want to left-join based on the first row per Table1.No_.
You can just add a row-number to Table2, then left-join and filter on the row-number.
SELECT
tA.No_,
tA.Description,
tA.Source,
tA.VGroup,
tB.Event
FROM Table1 tA
LEFT JOIN (
SELECT *,
rn = ROW_NUMBER() OVER (PARTITION BY tB.[No] ORDER BY tB.ID)
FROM Table2 tB
) tB ON tA.[No_] = tB.[No] AND tB.rn = 1;
Related
I am trying to build a SQL query to recover only the most young record of a table (it has a Timestamp column already) where the item by which I want to filter appears several times, as shown in my table example:
.
Basically, I have a table1 with Id, Millis, fkName and Price, and a table2 with Id and Name.
In table1, items can appear several times with the same fkName.
What I need to achieve is building up a single query where I can list the last record for every fkName, so that I can get the most actual price for every item.
What I have tried so far is a query with
SELECT DISTINCT [table1].[Millis], [table2].[Name], [table1].[Price]
FROM [table1]
JOIN [table2] ON [table2].[Id] = [table1].[fkName]
ORDER BY [table2].[Name]
But I don't get the correct listing.
Any advice on this? Thanks in advance,
A simple and portable approach to this greatest-n-per-group problem is to filter with a subquery:
select t1.millis, t2.name, t1.price
from table1 t1
inner join table2 t2 on t2.id = t1.fkName
where t1.millis = (select max(t11.millis) from table1 t11 where t11.fkName = t1.fkName)
order by t1.millis desc
using Common Table Expression:
;with [LastPrice] as (
select [Millis], [Price], ROW_NUMBER() over (Partition by [fkName] order by [Millis] desc) rn
from [table1]
)
SELECT DISTINCT [LastPrice].[Millis],[table2].[Name],[LastPrice].[Price]
FROM [LastPrice]
JOIN [table2] ON [table2].[Id] = [LastPrice].[fkName]
WHERE [LastPrice].rn = 1
ORDER BY [table2].[Name]
I have two tables.
Table1 is 1591 rows. Table2 is 270 rows.
I want to fetch specific column data from Table2 based on some condition between them and also exclude duplicates which are in Table2. Which I mean to join the tables but get only one value from Table2 even if the condition has occurred more than time. The result should be exactly 1591 rows.
I tried to make Left,Right, Inner joins but the data comes more than or less 1591.
Example
Table1
type,address,name
40,blabla,Adam
20,blablabla,Joe
Table2
type,currency
40,usd
40,gbp
40,omr
Joining on 'type'
Result
type,address,name,currency
40,blabla,name,usd
20,blblbla,Joe,null
try this it has to work
select *
from
Table1 h
inner join
(select type,currency,ROW_NUMBER()over (partition by type order by
currency) as rn
from
Table2
) sr on
sr.type=h.type
and rn=1
Try this. It's standard SQL, therefore, it should work on your rdbms system.
select * from Table1 AS t
LEFT OUTER JOIN Table2 AS y ON t.[type] = y.[type] and y.currency IN (SELECT MAX(currency) FROM Table2 GROUP BY [type])
If you want to control which currency is joined, consider altering Table2 by adding a new column active/non active and modifying accordingly the JOIN clause.
You can use outer apply if it's supported.
select a.type, a.address, a.name, b.currency
from Table1 a
outer apply (
select top 1 currency
from Table2
where Table2.type = a.type
) b
I typical way to do this uses a correlated subquery. This guarantees that all rows in the first table are kept. And it generates an error if more than one row is returned from the second.
So:
select t1.*,
(select t2.currency
from table2 t2
where t2.type = t1.type
fetch first 1 row only
) as currency
from table1 t1;
You don't specify what database you are using, so this uses standard syntax for returning one row. Some databases use limit or top instead.
I am trying to join my master table to some sub-tables in PostgreSQL in a single select query. I am getting a syntax error and I have the feeling I am making a terrible mistake or doing something which is not allowed. The code:
Select
id,
length,
other_stuff
from my_table tbl1
Left join
(
Select
id,
height
from my_table2 tbl2) tbl2 using (id)
left join
-- I get syntax error here
(
With a as (select id from some_table),
b as (Select value from other_table)
Select id, value from a, b) tbl3 using (id)
order by tbl1.id
Can we use WITH clause in left joins sub or nested queries and Is there a better way to do this?
UPDATE1
Well, I would like to add some more details. I have three select queries like this (having unique ID) and I want to join them based on ID.
Query1:
With a as (Select id, my_other records... from postgres_table1)
b as (select id, my_records... from postgres_table2)
c as (select id, my_record.. from postgres_table3, b)
Select
id,
my_records
from a left join c on some_condtion_with_a
order by 1
Second query:
Select
id, my_records
from
(
multiple_sub_queries_by_getting_records_from_c
)
Third Query:
With d as (select id, records.. from b),
e as (select id, records.. from d),
f as (select id, records.. from e)
select
id,
records..
from f
I tried to join them using left join. The first two queries were joined successfully. While, joining third query I got the syntax error. Maybe, I am complicating things thus I asked is there a better way to do it.
You are over complicating things. There is no need to use a derived table to outer join my_table2. And there is no need for a CTE plus a derived table to join the tbl3 alias:
Select id,
length,
other_stuff
from my_table tbl1
Left join my_table2 tbl2 using (id)
left join (
select st.id, ot.value
from some_table st
cross join other_table ot
) tbl3 using (id)
order by tbl1.id;
This assumes that the cross join you create with Select id, value from a, b is intended.
Not tested, but I think you need this. try:
with a as (select id from some_table),
b as (Select value from other_table)
Select
id,
length,
other_stuff
from my_table tbl1
Left join
(
Select
id,
height
from my_table2 tbl2
)
tbl2 using (id)
left join
(
Select id, value from a, b
)
tbl3 using (id)
order by tbl1.id
I've only ever seen/used WITH in the following format:
WITH
temptablename(columns) as (query),
temptablename2(columns) as (query),
...
temptablenameX(columns) as (query)
SELECT ...
i.e. they come first
You'll probably find it easier to write queries if you use indentation to describe nesting levels. I like to make my SELECT FROM WHERE GROUPBY ORDERBY at one indent level, and then tablename INNER JOIN ON etc more indented:
SELECT
column
FROM
table
INNER JOIN
(
SELECT subcolumn FROM subtable WHERE subclause
) myalias
ON
table.id = myalias.whatever
WHERE
blah
Organising your indents every time you nest down a layer really helps. By making everything that is "a table or a block of data like a table (i.e. a subquery)" indented the same amount you can easily see the notional order that the DB should retrieve
Move your WITHs to the top of the statement, you will still use the alias names in place in the sub sub query of course
Looking at your query, there isn't much point in your subqueries.. You don't do any grouping or particularly complex processing of the data, you just select an ID and another column and then join it in. Your query will be simpler if you don't do this:
SELECT
column
FROM
table
INNER JOIN
(
SELECT subcolumn FROM subtable WHERE subclause
) myalias
ON
table.id = myalias.whatever
WHERE
blah
Instead, do this:
SELECT
column
FROM
table
INNER JOIN
subtable
ON
table.id = subtable.id
WHERE
blah
Re your updated requirements, following the same pattern.
look for --my comments
With a as (Select id, my_other records... from postgres_table1)
b as (select id, my_records... from postgres_table2)
c as (select id, my_record.. from postgres_table3, b)
d as (select id, records.. from b),
e as (select id, records.. from d),
f as (select id, records.. from e)
SELECT * FROM
(
--your first
Select
id,
my_records
from a left join c on some_condtion_with_a
) Q1
LEFT OUTER JOIN
(
--your second
Select
id, my_records
from
(
multiple_sub_queries_by_getting_records_from_c
)
) Q2
ON Q1.XXXX = Q2.XXXX --fill this in !!!!!!!!!!!!!!!!!!!
LEFT OUTER JOIN
(
--your third
select
id,
records..
from f
) Q3
ON QX.XXXXX = Q3.XXXX --fill this in !!!!!!!!!!!!!!!!!!!
It'll work, but it might not be the prettiest or most necessary SQL arrangement. As both i and HWNN have said, you can rewrite a lot of these queries where you're just doing some simple selecting in your WITH.. But likely that theyre simple enough that the database optimizer can also see this and rerwite the query for you when it runs it
Just remember to code clearly, and lay your indentation out nicely to stop it tunring into a massive, unmaintainable, undebuggable spaghetti mess
I wrote this following query in Access.
I finally got it Save without errors but When I click on DataSheet View, the table displays all the records from table 2.
Table1 has unique ID and that ID is in multiple rows in table2 (1 to many). I need to only fetch the most recent record by selecting the Max(MyRecentDate). However, my return VIEW contains all the rows for the ID. How can I get this query to work to only select ONE record with the MAX Date from table2?
Thanks....
SELECT
[table1].FirstName,
[table1].MiddleName,
[table1].LastName,
[table2].NameDesc,
[table2].MyRecentDate
FROM [table1]
INNER JOIN
(
SELECT [table2].ID, [table2].NameDesc, MAX( [table2].MyRecentDate) as MyRecentDate
FROM [table2]
GROUP BY [table2].ID,[table2].NameDesc
) [table2]
ON [table1].[ID] = [table2].[ID];
This should work fine. Note you can use max in place of TOP 1
SELECT
[table1].FirstName,
[table1].MiddleName,
[table1].LastName,
(SELECT TOP 1 [table2].NameDesc FROM [table2] WHERE [table1].[ID] = [table2].[ID]) AS NameDesc,
(SELECT TOP 1 [table2].MyRecentDate FROM [table2] WHERE [table1].[ID] = [table2].[ID]) AS MyRecentDate
FROM [table1]
Here is my situation:
Table one contains a set of data that uses an id for an unique identifier. This table has a one to many relationship with about 6 other tables such that.
Given Table 1 with Id of 001:
Table 2 might have 3 rows with foreign key: 001
Table 3 might have 12 rows with foreign key: 001
Table 4 might have 0 rows with foreign key: 001
Table 5 might have 28 rows with foreign key: 001
I need to write a report that lists all of the rows from Table 1 for a specified time frame followed by all of the data contained in the handful of tables that reference it.
My current approach in pseudo code would look like this:
select * from table 1
foreach(result) {
print result;
select * from table 2 where id = result.id;
foreach(result2) {
print result2;
}
select * from table 3 where id = result.id
foreach(result3) {
print result3;
}
//continued for each table
}
This means that the single report can run in the neighbor hood of 1000 queries. I know this is excessive however my sql-fu is a little weak and I could use some help.
LEFT OUTER JOIN Tables2-N on Table1
SELECT Table1.*, Table2.*, Table3.*, Table4.*, Table5.*
FROM Table1
LEFT OUTER JOIN Table2 ON Table1.ID = Table2.ID
LEFT OUTER JOIN Table3 ON Table1.ID = Table3.ID
LEFT OUTER JOIN Table4 ON Table1.ID = Table4.ID
LEFT OUTER JOIN Table5 ON Table1.ID = Table5.ID
WHERE (CRITERIA)
Join doesn't do it for me. I hate having to de-tangle the data on the client side. All those nulls from left-joining.
Here's a set-based solution that doesn't use Joins.
INSERT INTO #LocalCollection (theKey)
SELECT id
FROM Table1
WHERE ...
SELECT * FROM Table1 WHERE id in (SELECT theKey FROM #LocalCollection)
SELECT * FROM Table2 WHERE id in (SELECT theKey FROM #LocalCollection)
SELECT * FROM Table3 WHERE id in (SELECT theKey FROM #LocalCollection)
SELECT * FROM Table4 WHERE id in (SELECT theKey FROM #LocalCollection)
SELECT * FROM Table5 WHERE id in (SELECT theKey FROM #LocalCollection)
Ah! Procedural! My SQL would look like this, if you needed to order the results from the other tables after the results from the first table.
Insert Into #rows Select id from Table1 where date between '12/30' and '12/31'
Select * from Table1 t join #rows r on t.id = r.id
Select * from Table2 t join #rows r on t.id = r.id
--etc
If you wanted to group the results by the initial ID, use a Left Outer Join, as mentioned previously.
You may be best off to use a reporting tool like Crystal or Jasper, or even XSL-FO if you are feeling bold. They have things built in to handle specifically this. This is not something the would work well in raw SQL.
If the format of all of the rows (the headers as well as all of the details) is the same, it would also be pretty easy to do it as a stored procedure.
What I would do: Do it as a join, so you will have the header data on every row, then use a reporting tool to do the grouping.
SELECT * FROM table1 t1
INNER JOIN table2 t2 ON t1.id = t2.resultid -- this could be a left join if the table is not guaranteed to have entries for t1.id
INNER JOIN table2 t3 ON t1.id = t3.resultid -- etc
OR if the data is all in the same format you could do.
SELECT cola,colb FROM table1 WHERE id = #id
UNION ALL
SELECT cola,colb FROM table2 WHERE resultid = #id
UNION ALL
SELECT cola,colb FROM table3 WHERE resultid = #id
It really depends on the format you require the data in for output to the report.
If you can give a sample of how you would like the output I could probably help more.
Join all of the tables together.
select * from table_1 left join table_2 using(id) left join table_3 using(id);
Then, you'll want to roll up the columns in code to format your report as you see fit.
What I would do is open up cursors on the following queries:
SELECT * from table1 order by id
SELECT * from table1 r, table2 t where t.table1_id = r.id order by r.id
SELECT * from table1 r, table3 t where t.table1_id = r.id order by r.id
And then I would walk those cursors in parallel, printing your results. You can do this because all appear in the same order. (Note that I would suggest that while the primary ID for table1 might be named id, it won't have that name in the other tables.)
Do all the tables have the same format? If not, then if you have to have a report that can display the n different types of rows. If you are only interested in the same columns then it is easier.
Most databases have some form of dynamic SQL. In that case you can do the following:
create temporary table from
select * from table1 where rows within time frame
x integer
sql varchar(something)
x = 1
while x <= numresults {
sql = 'SELECT * from table' + CAST(X as varchar) + ' where id in (select id from temporary table'
execute sql
x = x + 1
}
But I mean basically here you are running one query on your main table to get the rows that you need, then running one query for each sub table to get rows that match your main table.
If the report requires the same 2 or 3 columns for each table you could change the select * from tablex to be an insert into and get a single result set at the end...