I have SQL statement which takes really a lot of time to execute and I really had to improve it somehow.
select * from table where ID=1 and GROUP in
(select group from groupteam where
department= 'marketing' )
My question is if I should create index on columns ID and GROUP would it help?
Or if not should I create index on second table on column DEPARTMENT?
Or I should create two indexes for both tables?
First table has 249003.
Second table has in total 900 rows while query in that table returns only 2 rows.
That is why I am surprised that response is so slow.
Thank you
You can also use EXISTS, depending on your database like so:
select * from table t
where id = 1
and exists (
select 1 from groupteam
where department = 'marketing'
and group = t.group
)
Create a composite index on individual indexes on groupteam's department and group
Create a composite index or individual indexes on table's id and group
Do an explain/analyze depending on your database to review how indexes are being used by your database engine.
Try a join instead:
select * from table t
JOIN groupteam gt
ON d.group = gt.group
where ID=1 AND gt.department= 'marketing'
Index on table group and id column and table groupteam group column would help too.
Related
Please I use Sql Server
I have the Quantity field in the Items table equal to the sum of the Quantity fields in the Stocks table.
Is there a way to do this automatically in?
You could use an indexed view to hold the aggregation, which means that the server will maintain the view whenever there is any modification to the base tables. This removes the possibility of update anomalies.
CREATE VIEW vwTotalStock AS
SELECT i.ItemId, i.ItemName, SUM(s.Quantity) TotalQuantity
FROM dbo.Items i
JOIN dbo.Stocks s ON s.ItemId = i.ItemId
GROUP BY
i.ItemId, i.ItemName;
GO
CREATE CLUSTERED INDEX IX_vwTotalStock ON dbo.vwTotalStock (ItemId);
I use SQL Server 2014 and need to update a new added datetime type column in one table. There are two tables related (both have > 30 millions of records):
TableA:
CategoryID, itemID, dataCreated, deleted, some other string properties.
This table contains multiples records for each item with different datecreated.
TableB:
CategoryID, itemID, LatestUpdatedDate (This is the new added column)
both categoryID and itemID are part of an index on this table.
To update tableB's LatestUpdatedDate from table A on matched CategoryID and ItemID, I used the following merge statement:
merge [dbo].[TableB] with(HOLDLOCK) as t
using
(
select CategoryID,itemID, max(DateCreated) as LatestUpdatedDate
from dbo.TableA
where TableA.Deleted = 0
group by CategoryID,itemID
) as s on t.CategoryID = s.CategoryID and t.itemID = s.itemID
when matched then
update
set t.LatestUpdatedDate = s.LatestUpdatedDate
when not matched then
insert (CategoryID, itemID, LatestUpdatedDate)
values (s.CategoryID, s.itemID)
Given the fact that millions of records in both table, How can I optimize this script? Or Is there any other way to update the table with better performance?
Note: This is a one-off script and DB is on live, there would be a trigger added to tableA against insert to update the date in tableB in the future.
As per Optimizing MERGE Statement Performance, the best you can do is:
Create an index on the join columns in the source table that is unique and covering.
Create a unique clustered index on the join columns in the target table.
You may get a performance improvement during MERGE1 by creating an index on TableA on (Deleted, CategoryID, itemID) INCLUDE(DateCreated). However, since this is a one-off operation, the resources (time, CPU, space) required to create this index probably won't offset the performance gains vis-a-vis running the query as-is and relying on your existing index.
I have a problem where I need to check that two columns in each table in a database are unique.
We have the database with barcode entries called uid and rid.
Table 1: T1.uid
And
Table 2: T2.rid
No barcodes in the two table columns must be the same.
How can we ensure that.
If a insertion of a barcode into table T1.uid matches an entry in
T2.rid we want to throw an error.
The tables are cleaned up and is in a consistent state where the entries in
T1.uid and T2.rid are unique over both table columns.
It is not possible to insert NULL values in the tables respective uid and tid column(T1.uid and T2.rid)
It is not possible to create a new table for all barcodes.
Because we don't have full control of the database server.
EDIT 19-02-2015
This solution cannot work for us, because we cannot make a new table
to keep track of the unique names(see table illustration).
We want to have a constraint over two columns in different tables without changing the schema.
Per the illustration we want to make it impossible for john to exist in
T2 because he already exists in table T1. So an error must be "thrown"
when we try to insert John in T2.Name.
The reason is that we have different suppliers that inserts into these tables
in different ways, if we change the schema layout, all suppliers would
need to change their database queries. The total work is just to much,
if we force every suppplier to make changes.
So we need something unobtrusive, that doesnt require the suppliers to change
their code.
A example could be that T1.Name is unique and do not accept NULL values.
If we try insert an existing name, like "Alan", then an exception will occur
because the column has unique values.
But we want to check for uniqueness in T2.Name at the same time.
The new inserted value should be unique over the two tables.
Maybe something like this:
SELECT uid FROM Table1
Where Exists (
SELECT rid FROM Table2
WHERE Table1.uid = rid )
This will show all rows from Table1 where their column uid has an equivalent in column rid of Table2.
The condition before the insertion happens could look like below. #Idis the id you need to insert the data for.
DECLARE #allowed INT;
SELECT #allowed = COUNT(*)
FROM
(
SELECT T1.uid FROM T1 WHERE T1.uid = #Id
UNION ALL
SELECT T2.rid FROM T2 WHERE T2.rid = #id
)
WHERE
#id IS NOT NULL;
IF #allowed = 0
BEGIN
---- insert allowed
SELECT 0;
END
Thanks to all who answered.
I have solved the problem. A trigger is added to the database
everytime an insert or update procedure is executed, we catch it
check that the value(s) to be inserted doens't exist in the columns of the two
tables. if that check is succesfull we exceute the original query.
Otherwise we rollback the query.
http://www.codeproject.com/Articles/25600/Triggers-SQL-Server
Instead Of Triggers
What I have:
1 table(table is in both DB's)
2 databases(currently used + archived from last year(old))
"ID" is the primary key for the table.
my issue:
archived database table has rows in it that is not present in the currently used database table. Can anyone tell me how I go about updating the currently used database table from the old database table(i.e. insert * unique rows from old database table into new database table)
It sounds simple enough but wanted some advice before proceeding as I DO NOT want duplicate rows, I just want to throw the rows in the old table(that IS NOT present in the currently used database table) into the new one(copy only is fine).
I hope I explained clearly enough.
Insert rows from the new table only if row with same id not exists in old table:
insert into old_table select * from new_table nt
where not exists (select 1 from old_table
where id = nt.id)
(Specifying columns, both inserted and selected, is nice - but I'm lazy here...)
You can usually address tables from other databases by prefixing the database name: new_db.foo_table or old_db.foo_table. This way you can look for rows in the old table that have no duplicates in the new table:
select *
from old_db.foo_table as old_foo
where not exists (
select 1
from new_db.foo_table as new_foo
where new_foo.key_field = old_foo.key_field
-- add more comparisons as needed
);
Then you can use the insert into new_db.foo_table select ... syntax to put the records into the new table.
Use LEFT JOIN filtering NULLs in target table. I think it will be faster
INSERT INTO NEW_TABLE
SELECT ot.* FROM OLD_TABLE ot
LEFT JOIN NEW_TABLE nt on ot.ID = nt.ID
WHERE nt.ID IS NULL
I'm trying to create a procedure that can create a table with not specific number of columns.
My query returns a value of 3 meaning it needs 3 columns (has to be dynamic).
I have create a #variable to set the name string of the tables but I don't know how to formulate the CREATE TABLE statement to actually create the table with the columns from this string.
Any kind of help would be appreciated guys.
You can get the columns on a table out of the sql database with
select
bb.name,
bb.colid
from sysobjects aa
inner join syscolumns bb
on aa.id = bb.id
where aa.name ='tblMyTable'
The name is the column name, the ID the number. You could select column names from the list and use dynamic sql to build a select. Not sure how you decide what columns you are after from the table.