[CASSANDRA-16916] Add support for IF EXISTS and IF NOT EXISTS in ALTER statements

• Type: Improvement
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 4.1-alpha1, 4.1
• Component/s: CQL/Syntax
• Change Category: Semantic
• Complexity: Low Hanging Fruit
• Platform: All

Source Control Link

https://github.com/apache/cassandra/commit/e137c7c34cc10d4f8c9124c6f9af17a44061ab1f

Test and Documentation Plan

The patch add some new unit tests

• Assignee: Jogesh Anand
• Reporter: Benjamin Lerer

Authors

Jogesh Anand

Reviewers

Benjamin Lerer, Berenguer Blasi

• Created: 03/Sep/21 15:42
• Updated: 09/Jul/24 13:18
• Resolved: 04/Apr/22 09:40

Description

It would make sense to add support for IF EXISTS and IF NOT EXISTS in the different ALTER statements.

For example:

• ALTER TABLE IF EXISTS myTable ...
• ALTER TABLE myTable ADD IF NOT EXISTS ...
• ALTER TABLE myTable DROP IF EXISTS ...
• ALTER TYPE IF EXISTS myType ...
• ALTER TYPE myType ADD IF NOT EXISTS ...

Additional info for newcomers:

In order to implement this change you will need to change the Parser.g ANTLR file located in the src/antlr directory and the java classes corresponding to the different alter statements located in the org.apache.cassandra.cql3.statements.schema package. You can look at the CreateTableStatement class to see how it was done there.
The unit test for the CQL logic are located under org.apache.cassandra.cql3.validation

Issue Links

• causes: CASSANDRA-19749 ALTER USER | ROLE IF EXISTS creates a user / role if it does not exist
• is duplicated by: CASSANDRA-14706 Support "IF EXISTS/IF NOT EXISTS" for all clauses of "ALTER TABLE"
• links to: trunk-16916