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https://issues.apache.org/jira/browse/CASSANDRA-20331?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17928170#comment-17928170
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Lukasz Antoniak commented on CASSANDRA-20331:
---------------------------------------------

Java driver does not pre-evaluate constraints to prevent sending invalid CQL 
query to the server. However, it maintains metadata API for the client 
application, see: 
[https://github.com/apache/cassandra-java-driver/blob/4.x/core/src/main/java/com/datastax/oss/driver/api/core/metadata/schema/TableMetadata.java.]
 System schema already contains definition of all tables, columns, functions, 
indexes, so from completeness perspective, I guess it would be good to contain 
constraint metadata also.

> Expose constraints in system_schema.column_constraints
> ------------------------------------------------------
>
>                 Key: CASSANDRA-20331
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-20331
>             Project: Apache Cassandra
>          Issue Type: Task
>          Components: Feature/Constraints
>            Reporter: Stefan Miklosovic
>            Assignee: Bernardo Botella Corbi
>            Priority: Normal
>             Fix For: 5.x
>
>          Time Spent: 20m
>  Remaining Estimate: 0h
>
> There is already system_schema.column_masks 
> {code}
> CREATE TABLE system_schema.column_masks (
>     keyspace_name text,
>     table_name text,
>     column_name text,
>     function_argument_nulls frozen<list<boolean>>,
>     function_argument_types frozen<list<text>>,
>     function_argument_values frozen<list<text>>,
>     function_keyspace text,
>     function_name text,
>     PRIMARY KEY (keyspace_name, table_name, column_name)
> ) WITH CLUSTERING ORDER BY (table_name ASC, column_name ASC)
> {code}
> We need this table with constraints of each column, similar to masks. Right 
> now there is no programmatic way to realize what constraints a column has. 
> This will come handy when Java Driver will start to support this. They will 
> just scan system_schema.column_constraints and they can e.g. fail the query 
> on client side it will never reach the server ... 



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