#Mysql server Sequence

That maybe possible with some ninja-like trickery, but you might not want to do that using expression rule.

In Appian, the number of times expression get evaluated is not guarantee. So if your rule created any side effects (triggered the DB sequence, in this case), you don't have full control of how many times the "side effect" will happen.

"Side Effect" is defined as any changes in the system caused by the rule or function called, other than the returned value itself.

docs.appian.com/.../Expressions.html

To make changes such as triggering DB sequence, you should use one of DB Smart Services available. This should do it for you:

docs.appian.com/.../Query_Database_Smart_Service.html

Can you elaborate on your use case, specifically why an expression rule?
In my experience, sequences are not an informative piece of info to end users until something is created. For example, help desk ticket submitted gets a number or contract created gets a sequence plus locale. In these cases, I will generally either use the write to ds (and store the output) to get the id and email or present it to user. If I just need a sequence, not a generated value in insert to a table I use query rdbms node ore even stored proc plugin.
Will that work for you?

Can you elaborate on your use case, specifically why an expression rule?
In my experience, sequences are not an informative piece of info to end users until something is created. For example, help desk ticket submitted gets a number or contract created gets a sequence plus locale. In these cases, I will generally either use the write to ds (and store the output) to get the id and email or present it to user. If I just need a sequence, not a generated value in insert to a table I use query rdbms node ore even stored proc plugin.
Will that work for you?

Thanks Christine and rawich for the response ,
If we want implement sequence in CDT field level is it possible , if it is possible then what is the syntax for it.
Thanks In Advance

venkateshs329 what i understood from your explanation is you want to insert the PrimaryKey value from your end rather than auto Generate, that too sequentially, like something-1, something-2, something-3 etc.., i am not sure, are you looking for this or something else, but if this is your requirement, then create a queryentity to fetch totalcount and create a rule and append the totalcount with the character, and also make your CDT PK of type Text. again i am not sure, whether you are looking for this or something else

Aloks:
Yes exactlly i want enter primary key from MY end , As you said we can create query entity and get totalCount
but if multiple users are using same CDT may be some duplicate entry chances are there. So if we implement DB Sequence there is no chance for Duplicate entries.
If am wrong please correct me ,
Thanks In Advance.

venkateshs329 in case if multiple users are working on the same CDT in that case you can have 2 options
1. Try to fetch and append the Manual PK value just before the Write to Data Store Node
2. Try to use Version to avoid concurrency