I am trying to do an SQL query on two tables to retrieve multiple columns with a certain column (PostID) to be distinct (and it is not the primary key of the that table).
In addition, I need the selected distinct rows to be the latest (one of the columns retrieved is the entry date).
Detailed description:
I am building a forum like application, using 3 tables to store data.
I use table1 to store user details, table2 to store the meta data for posts, table3 to store the post details, updates, and replies (postID is unique in table2 pointing towards an original post, while in table3, it is used to show the original post and updates and replies).
Table columns:
table1 (UserID, FullName, mobile, etc.)
table2 (postID, UserID, EntryDate, Deleted columns)
table3 (postdetailsId, PostID, UserID, Entrydate, etc.)
I am trying to retrieve all the posts for 1 user in a gridview, my SQL query uses the USERID to retrieve all his posts from the table. However, it is retrieving the original post and all its updates, and I only want to retrieve the latest update of each post.
How can it be done fully in SQL (I know I can do it in C# with the returned results)?
My query:
SELECT T1.FullName, T3.PostID, T3.EntryDate, T3.Title
FROM Table1 as T1, Table3 as T3
WHERE T3.UserID = T1.UserID
AND T3.UserID = #UserID
You could use GROUP BY PostID along with MAX(EntryDate)
SELECT *
FROM (
SELECT posts.*, ROW_NUMBER() OVER (PARTITION BY post_updates.UserID, post_updates.PostID ORDER BY post_updates.EntryDate DESC) AS rn
FROM table1 users
JOIN table3 post_updates
ON post_updates.userID = users.UserID
WHERE users.UserID = #UserID
) q
WHERE rn = 1
Related
Using SQLite I can get all tablenames in my database:
SELECT name AS Tablename FROM sqlite_master WHERE type = 'table'
Result will be some tablenames, for example:
Tablename:
cars
planes
bus
How could I have a SQL query that will count the number of records for each table that is found, result should be:
Tablename Records:
cars 100
planes 200
bus 300
I understand that in this example I simply could run 3 SELECT COUNT() statements, however the number of tables can vary so that I can not hardcode a fixed number of SELECT COUNT()
All table and column names in a statement need to be known at the time it is compiled, so you can't do this dynamically.
You'd have to programmatically build up a new query string based on the results of getting the table names from sqlite_master. Either one query per table like you mentioned, or all together by creating something that looks like
SELECT 'table1' AS Tablename, count(*) AS Records FROM table1
UNION ALL
SELECT 'table2', count(*) FROM table2
-- etc.
You don't mention what language you're working in, so in psuedo-code of a functional style:
var allcounts = query("SELECT name FROM sqlite_master WHERE type = 'table'")
.map(name -> "SELECT '$name' AS Tablename, count(*) AS Records FROM \"$name\"")
.join(" UNION ALL ");
var totals = query(allcounts);
I am creating a app with ionic 3. In the app I added a search filter which filter users according to their role. I have 5 tables from which I have to pull the data.In term to do so, I did these steps..
created each table index with the required data.
CREATE INDEX IF NOT EXISTS AccountIndexTable ON Accounts(id,roleId,firstName,lastName,email,accountId);
CREATE INDEX IF NOT EXISTS AddressIndexTable ON Addresses(id,addressTypeId,street,city,state,country,pincode,accountId)
CREATE INDEX IF NOT EXISTS CompanyIndexTable ON Companies(id,name,accountId)
CREATE INDEX IF NOT EXISTS CommunicationIndexTable ON Communications(id,phone,accountId)
CREATE INDEX IF NOT EXISTS OptionalInfoIndexTable ON CustomerOptionalInfos(id,customerType,accountId)
and then i used join to get data. Before that I have questions
1: Do I need to use the indexed table in my join?
the Join query:
SELECT Accounts.accountId AS accountID,
Accounts.roleId AS roleID,
Accounts.email AS email,
Accounts.firstName || " " || Accounts.lastName AS name,
Addresses.street AS street,
Addresses.city AS city,
Addresses.state AS state,
Addresses.country AS country,
Addresses.pincode AS pincode,
Communications.phone AS phone,
Companies.name AS compName,
CustomerOptionalInfos.customerType AS cType
FROM Accounts
LEFT JOIN Addresses ON Addresses.accountId=Accounts.accountId
AND Addresses.addressTypeId=1
LEFT JOIN Communications ON Communications.accountId=Accounts.accountId
LEFT JOIN Companies ON Companies.accountId=Accounts.accountId
LEFT JOIN CustomerOptionalInfos ON CustomerOptionalInfos.accountId=Accounts.accountId
WHERE 1=1
AND Accounts.isDelete!='true'
AND Accounts.firstName!= ''
AND Accounts.roleId = 5
ORDER BY Accounts.firstName ASC
LIMIT ?,?
It still takes +2 seconds to execute. Please suggest me the better way of doing this. I have a large number of data.
Imagine, that I need to retrieve all records excluding, those, that are associated
with specific ID, for instance if you consider table below and chose RestaurantID 1, resulting table should not include rows, that contain CuisineID 3,4 and 7.
If RestaurantID is 6, then resulting table should return anything without CuisineID 1 and 8
and so on
My table
Kind regards
erwre
if you do a subselect with your query, you can get a list of which CuisineID's to exclude using the NOT IN clause.
select
t.*
from
mytable t
where
t.CuisineID NOT IN
(
select
t2.CuisineID
from
mytable t2
where
t2.ID = #YOUR_RESTAURANT_ID
)
I am passing datatable as input parameter to stored procedure. Datatable contains id, Name,Lname,Mobileno,EmpId.
Employee table contains [Name],[Lname],[mobno],[Did] as columns.
When user is logged in, his Id come as DId. There are more than 1000 records. Instead of passing that id to datatable, I have created
separete parameter to sp. I want to add records to Employee table, which are not already exist. If combination of mobileno and Did already exists, then
don't insert into Employee table, else insert. Datatable may contain records, which can be duplicate. So I don't want to include that record. I want select only
distinct records and add them to table. I am intrested in mobile no. If there are 10 record having same moble no, I am fetching record, which comes first.
Following code is right or wrong. According to my knowledge, first from clause, then inner join, then where, then select execute. Record get fetched from datatable,
then inner join happens generate result, from that result not from datatable it will check record. So it will give me proper output.
Create Procedure Proc_InsertEmpDetails
#tblEmp EmpType READONLY,
#DId int
as
begin
INSERT INTO Employee
([Name],[Lname],[mobno],[Did])
SELECT [Name],[Lname],[mobno] #DId
FROM #tblEmp A
Inner join (
select min(Id) as minID, mobno from #tblEmp group by mobno
) MinIDTbl
on MinIDTbl.minID = A.ExcelId
WHERE NOT EXISTS (SELECT 1
FROM Employee B
WHERE B.[mobno] = A.[mobno]
AND B.[Did] = #DId )
end
or does I need to change like this
INSERT INTO Employee
([Name],[Lname],[mobno],[Did])
SELECT C.[Name],C.[Lname],C.[mobno], C.D_Id
from
(SELECT [Name],[Lname],[mobno] #DId as D_Id
FROM #tblEmp A
Inner join (
select min(Id) as minID, mobno from #tblEmp group by mobno
) MinIDTbl
on MinIDTbl.minID = A.ExcelId
)C
WHERE NOT EXISTS (SELECT 1
FROM Employee B
WHERE B.[mobno] = C.[mobno]
AND B.[Did] = #DId )
I have a table and a relation
I have maybe 10 Submissions, but when I query the database I only want to get those with a Unique CaseId and the one to return should be the one with the newest Date. Is it possible (And adviceable) to do this in a single query or should I do the filtering in my asp.nets code behind where I fetch the data?
Edit: New images
Here you can see that I show many items with the same case id, I only want to show the latest one (Based on date)
This is my current sql query
SELECT Submission.Id, Date, center.Name as CenterName, center.Id as CenterId, subject.Name as SubjectName, subject.Id as SubjectId, EmployeeName, Reason, Description, Explanation, Done, ChiefLevel, Action, CaseId
FROM Submission, subject, center
WHERE center.Id=CenterId AND subject.Id=SubjectId
ORDER BY Date DESC;
SELECT caseid
FROM
(
SELECT caseid, max(date) AS max_date
FROM submission
GROUP BY caseid
) a
JOIN subject t ON a.subjectid=t.id
My QUERY ended up being this
SELECT s.Id, s.Date, c.Name as CenterName, c.Id as CenterId, su.Name as SubjectName, su.Id as SubjectId, s.EmployeeName, s.Reason, s.Description, s.Explanation, s.Done, s.ChiefLevel, s.Action, s.CaseId
FROM submission as s
INNER JOIN
(
SELECT CaseId, MAX(Date) AS MaxDateTime
FROM submission
GROUP BY CaseId
) as groupeds
ON s.CaseId = groupeds.CaseId
AND s.`Date` = groupeds.MaxDateTime
INNER JOIN
(
SELECT Id, Name
FROM subject
) as su
ON su.Id=SubjectId
INNER JOIN
(
SELECT Id, Name
FROM center
) as c
ON c.Id=CenterId;