[jira] [Comment Edited] (DERBY-6991) GROUP_CONCAT

["Rick Hillegas (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-6991?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16414891#comment-16414891 ] 

Rick Hillegas edited comment on DERBY-6991 at 3/27/18 12:37 PM:
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It is a large, complicated codebase. The best place to start would be to study the patches attached to DERBY-5466. Those are the classes which will need to be touched in order to implement LISTAGG. You should also read the architecture documents nested under "Derby Engine" under "Papers and Presentations" in the left pane of the resources tab on the Derby website. See http://db.apache.org/derby/papers/derby_arch.html

The main processing phases of a SQL database are as follows:

1) Parsing - This is the task of converting a SQL query into an abstract syntax tree (AST). The main class involved here is java/engine/org/apache/derby/impl/sql/compile/sqlgrammar.jj. That file is the SQL grammar, written in JavaCC. See java/engine/org/apache/derby/impl/sql/compile/sqlgrammar.jj

2) Binding - This is the task of revolving names and datatypes in the AST. This task and the remaining compilation tasks are performed largely by the AST nodes themselves. The AST nodes live alongside the grammar in trunk/java/engine/org/apache/derby/impl/sql/compile. The main AST nodes involved in implementing LISTAGG would be AggregateNode and UserAggregateDefinition. All AST nodes descend from the superclass QueryTreeNode. Methods with the word "bind" in them are the workhorses of the binding phase.

3) Optimization - You don't have to worry about this phase. There are no additional optimization decisions to make during the compilation of user-defined aggregates.

4) Code-generation - Again, this task is performed by the AST nodes themselves. In this phase, the AST tree is transformed into a graph of executable nodes called the query plan. The executable nodes live in java/engine/org/apache/derby/impl/sql/execute. The main class for implementing LISTAGG is UserDefinedAggregator. Code generation is performed by methods with the word "generate" in them.

5) Execution - The execution logic would be an implementation of java/engine/org/apache/derby/agg/Aggregator.java.

Take some time to study these classes, the architecture docs, and the work which was done on DERBY-5466. Feel free to ask lots of questions.

Thanks,
-Rick



was (Author: rhillegas):
It is a large, complicated codebase. The best place to start would be to study the patches attached to DERBY-5466. Those are the classes which will need to be touched in order to implement LISTAGG. You should also read the architecture documents nested under "Derby Engine" under "Papers and Presentations" in the left pane of the resources tab on the Derby website. See http://db.apache.org/derby/papers/derby_arch.html

The main processing phases of a SQL database are as follows:

1) Parsing - This is the task of converting a SQL query into an abstract syntax tree (AST). The main class involved here is java/engine/org/apache/derby/impl/sql/compile/sqlgrammar.jj. That file is the SQL grammar, written in JavaCC. See java/engine/org/apache/derby/impl/sql/compile/sqlgrammar.jj

2) Binding - This is the task of revolving names and datatypes in the AST. This task and the remaining compilation tasks are performed largely by the AST nodes themselves. The AST nodes live alongside the grammar in trunk/java/engine/org/apache/derby/impl/sql/compile. The main AST nodes involved in implementing LISTAGG would be AggregateNode and UserAggregateDefinition. All AST nodes descend from the superclass QueryTreeNode. Methods with the word "bind" in them are the workhorses of the binding phase.

3) Optimization - You don't have to worry about this phase. There are no additional optimization decisions to make during the compilation of user-defined aggregates.

4) Code-generation - Again, this task is performed by the AST nodes themselves. In this phase, the AST tree is transformed into a graph of executable nodes called the query plan. The executable nodes live in java/engine/org/apache/derby/impl/sql/execute. The main class for implementing LISTAGG is UserDefinedAggregator. Code generation is performed by methods with the word "generate" in them.

5) Execution - The query plan is then run.

Take some time to study these classes, the architecture docs, and the work which was done on DERBY-5466. Feel free to ask lots of questions.

Thanks,
-Rick


> GROUP_CONCAT
> ------------
>
>                 Key: DERBY-6991
>                 URL: https://issues.apache.org/jira/browse/DERBY-6991
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 10.15.0.0
>            Reporter: The Alchemist
>            Priority: Minor
>
> I was wondering what it would take to get {{GROUP_CONCAT()}} support.
>  
> If someone points me in the right direction, I can send a patch.



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