I am working on a heavy record set database in MS SQL 2016. So I want to use row table partition feature to improve speed.
As we know partition feature is working on partition column of a table. Let's say [Date Column] of a table. In our scenario, have many tables that need to partition because of heaver record set in 5 to 7 tables. Each table not have that [Date column]. Also not possible to add that column in each table.
So is there any way I can select partition column of another table or something else.
The best option is to add a common column to all tables that you will then use to partition by.
You must already have a way of relating the different tables to each other so you can use this to tag each table with the correct Partition column.
This column could be as simple as an int with YYYYMM as values for monthly partitions.
You also need to make sure your queries are "Partition Aware".
This means that you should include this column in your WHERE Clause and also your JOIN Clauses for any queries.
Use Query Plans to make sure you are getting Partition Elimination on your queries.
If you can't change the model (but can add partitions???) then you could implement the partitioning with different columns in each table provided you have a single column in each table that you can partition on named ranges - but if you have 1-many relationships then it is unlikely that the child tables keys will be consecutive relative to the parent table. Note that this approach will make your "partition aware" queries more complex to craft.
Related
I have a table in snowflake with around 1000 columns, i have an id column which is of integer type
when i run query like
select * from table where id=12
it is scanning all the micro-paritions .I am expecting that snowflake will maintain metadata of min/max of id column and based on that it should scan only one partition rather than all the partition.
In this doc https://docs.snowflake.com/en/user-guide/tables-clustering-micropartitions.html its mentioned that they maintain min/max , disticnt value of columns in each micro-partition.
How can i take advantage of partititon pruning in this scenario?Currently even for unique id snowflake is scanning all the partitions.
It's a little more complicated than that unfortunately. Snowflake would only scan a single partition if your table was perfectly clustered by your id column, which it probably isn't, nor should it be. Snowflake is a data warehouse and isn't ideal for single-row lookups.
You could always cluster your table by your id column but you usually don't want to do this in a data warehouse. I would recommend reading this document to understand how table clustering works.
Is there any way of converting the last a.ROWID > b.ROWID values in below code in to snowflake? the below is the oracle code. Need to take the ROW ID to snowflake. But snowflake does not maintain ROW ID. Is there any way to achieve the below and convert the row id issue?
DELETE FROM user_tag.user_dim_default a
WHERE EXISTS (SELECT 1
FROM rev_tag.emp_site_weekly b
WHERE a.number = b.ID
AND a.accountno = b.account_no
AND a.ROWID > b.ROWID)
So this Oracle code seem very broken, because ROWID is a table specific pseudo column, thus comparing value between table seem very broken. Unless the is some aligned magic happening, like when user_tag.user_dim_default is inserted into rev_tag.emp_site_weekly is also written. But even then I can imagine data flows where this will not get what you want.
So as with most things Snowflake, "there is no free lunch", so the data life cycle that is relying on ROW_ID needs to be implemented.
Which implies if you are wanting to use two sequences, then you should do explicitly on each table. And if you are wanting them to be related to each other, it sounds like a multi table insert or Merge should be used so you can access the first tables SEQ and relate it in the second.
ROWID is an internal hidden column used by the database for specific DB operations. Depending on the vendor, you may have additional columns such as transaction ID or a logical delete flag. Be very carful to understand the behavior of these columns and how they work. They may not be in order, they may not be sequential, they may change in value as a DB Maint job runs while your code is running, or someone else runs an update on a table. Some of these internal columns may have the same value for more than one row for example.
When joining tables, the RowID on one table has no relation to the RowID on another table. When writing Dedup logic or delete before insert type logic, you should use the primary key, and then additionally an audit column that has the date of insert or date of last update in combo with that. Check the data model or ERD digram for the PK/FK relationships between the tables and what audit columns are available.
I had partitioned my table in azure sql by referring below doc.
https://www.mssqltips.com/sqlservertip/2888/how-to-partition-an-existing-sql-server-table/
I need to know that whether the partitioned column should be always used in the where clause of the select query to scan through partition or direct select will achieve that?
I am using Azure SQL. I found the select performance of table partition is slower than the original. Can Sql Server table partition actually improve the select performance? As the Partition count increases the query performance degrades (i.e. 36 partition, 915 partition).
Also, what's the method to avoid partition scan and do normal table heap scan in a partitioned table?
1.About Partitioned Tables.
If your table has large data, you can use the table and index partitioning.
One of the benefits of partitioning is that:
You may improve query performance, based on the types of queries you frequently run and on your hardware configuration. For example, the query optimizer can process equi-join queries between two or more partitioned tables faster when the partitioning columns in the tables are the same, because the partitions themselves can be joined.
Here is the documentation:Partitioned Tables and Indexes
When you run the select query of a partition table, the query will search from your partitions until the data you need is found. So the select performance may be slower than original sometimes.
2.When your table is creating, you must need to specify if it is the partition table. Once the table is created as the partition table, you could not change it. I didn't find the method for you, I guess maybe that's not supported.
I hope it can helps you.
why can't we use Order By clause while creating the view. What is the reason behind SQL supporting Order by clause with TOP clause mentioned in the query and not supporting the same without TOP clause
A view is nothing but a virtual table and the order in which data is stored in a table can never be guaranteed in any RDBMS.
What you will need to do is:
SELECT <Column1>,<Column2>,....,<ColumnN>
FROM <MyView>
ORDER BY <MyColumn>
Because the tsql is relational and view is a relation and the relation doesn't have order.
In SQL, a view is a virtual table based on the result-set of an SQL statement. A view contains rows and columns, just like a real table. The fields in a view are fields from one or more real tables in the database.
You can add SQL functions, WHERE, and JOIN statements to a view and present the data as if the data were coming from one single table.
For ordering the resulted data you need to query it and apply order by clause as per your requirement.