Sql-Server

If you want to learn a lot about how Snowflake works internally, it’s worth spending some time reading the ACM whitepaper that described the service.

It describes the overall structure of the service, and then describes how data is stored, followed by a description of how the encryption of the data within the service is accomplished. (I’ll talk more about the management of encryption keys in a later blog post).

2019-11-08

Another question that I recently saw on Stack Overflow was asking how you SELECT a bunch of transactions back past a cutoff date, add them up, INSERT a roll-up row, and then delete the old ones. The concern was with how you make sure the ones you are deleting are the same rows that you are rolling up (or totalling). Someone else might UPDATE or INSERT a row at the same time.

2019-11-07

More and more users of SDU Tools are adding the deployment of the tools into their standard deployment pipelines, and into their standard operating environments (SOEs).

One common but simple request that we’ve had is that they need to be able to check which version of SDU Tools is currently installed. So we added a function to do that.

It doesn’t take any parameters but just returns the version number as a string.

2019-11-06

Another important concept when you’re working with strings is the concept of Collations. If I write code like the first line here:

The question is how would I know if a capital A is treated the same as a lower case A. The answer to that is “it depends upon the collation”. Collations are sets of rules that determine how strings are compared. SQL Server supports lots of collations. You can see them all by executing:

2019-11-04

Similar to SQL Server, Snowflake has ways of creating programmable objects. But the way they work, and the way they are created is quite different.

Functions

Functions are the most similar. You can create them in two ways:

• Javascript
• T-SQL

I like the idea that you can choose which language to write code in, and that they both end up extending the Snowflake SQL language pretty much the same. Some code is better written in T-SQL and other code is better written in a higher-level language.

2019-11-01

In Stack Overflow, I saw a poster with a query like this:

select * from student where stud_id in (
'5',
'3',
'4'
)

And he was frustrated that he couldn’t reliably get an ordered output like this:

id|   name  |
5 |  John   |
3 |  Erik   |
4 | Michael |

The problem is that he was assuming that the IN clause had a specified order that was then obeyed by the SELECT statement.

2019-10-31

Finishing up my recent theme of running queries against the SQL Server Reporting Services catalog. I often need to list which users have access to which items in the SSRS catalog.

So, in our free SDU Tools for developers and DBAs, we added a procedure that does just that. It’s called RSListUserAccessToContent.

It takes two optional parameters:

@RSDatabaseName sysname - the name of your SSRS database

@IsOrderedByUserName bit - should the output be ordered by user name?

2019-10-30

Over the years, I have long periods where I avoid Q&A forums. Lately, I’ve been spending a bit of time back in some forums. And once again, I’ve seen the sorts of behavior that make me think about leaving again.

Here’s a simple message: If you don’t like answering questions in Q&A forums, then don’t. Leave. You might think it’s all about you and your attempts to gain reputation in the forums. It’s not.

2019-10-29

When we write string literal values, we need to surround them in single quotes. There are options in some SQL products we could make that double quotes. In general though, don’t do that. Just use single quotes.

If you have multi byte characters, they need to be preceded by the N prefix. I’ve previously mentioned that it stands for National Character Set. If I don’t use the N, when I execute the second query, I’d see this:

2019-10-28

When you are loading data into Snowflake, it’s really important to achieve the maximum parallelism that you can. You want as many files loading in parallel as you have. I mentioned in earlier posts that the number of servers that you have, and the size of each of those servers, will determine the number of processor threads that are available to you from your virtual warehouses.

It would be pointless to have 32 processor threads waiting to load your data, and you provide Snowflake with one large file to load.

2019-10-25