Tom Tom - 4 months ago 27
SQL Question

Prevent error when dropping not existing sequences, creating existing users

I have a bunch of sql scripts that create / drop sequences, users and other objects. I'm running these scripts through liquibase, but they fail because oracle complains when I try to drop a non existing sequence, or create an existing user.

Is there an oracle way to prevent errors from happening?

Something of the sort


Create User / Sequence if not exists

Drop User/ Secuence if exists


As far as I know, I have these options:


  • Write a plsql script

  • Use liquibase contexts.

  • Use liquibase preconditions, but this would mean too much work.



Any thoughts / ideas will be greatly appreciated.

Answer

Liquibase has a failOnError attribute you can set to false on changeSets that include a call that could fail.

<changeSet failOnError="false">
   <createSequence sequenceName="new_sequence"/>
</changeSet>

This allows you to have simple create user, create sequence, drop user, and drop sequence changeSets and if the statement throws an error because they users/sequences exist/don't exist they will still be marked as ran and the update will continue.

The downside of this approach is that it will also mark them as ran and continue if they error for some other reason (bad permissions, connection failure, invalid SQL, etc.) The more accurate approach is to use preconditions, like this:

<changeSet>
   <preconditions onFail="MARK_RAN"><not><sequenceExists/></not></preconditions>
   <createSequence name="new_sequence"/>
</changeSet>

There is no userExists precondition currently, but you can create custom preconditions or fall back to the precondition. See http://www.liquibase.org/documentation/preconditions.html for documentation

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