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https://issues.apache.org/jira/browse/COMDEV-489?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17697050#comment-17697050
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Gael Yimen Yimga commented on COMDEV-489:
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Hello Mentors,
I started looking into this ticket and I have been investigating and debugging
the *select_char* operator. Here is the beginning of my
[thoughts|https://github.com/apache/shardingsphere/discussions/24097#discussioncomment-4996681].
I would like to give a proposal on how to solve the problem.
My findings are the following :
* I notice that for most of the MySQL functions, they are parsed as
`*ExpressionSegment*`.
* That `*ExpressionSegment*` is converted into `*FunctionSegment*`.
* But the `*FunctionSegment*` that is supposed to have the parameters set does
not have it.
The solution could be to find a mechanism to populate the parameters of
`*FunctionSegment*` as a list of `*ExpressionSegment*`. By doing so the
solution can fix al test case for the MySQL functions.
Please let me know what you think about.
> Apache ShardingSphere: Enhance SQLNodeConverterEngine to support more MySQL
> SQL statements
> ------------------------------------------------------------------------------------------
>
> Key: COMDEV-489
> URL: https://issues.apache.org/jira/browse/COMDEV-489
> Project: Community Development
> Issue Type: Improvement
> Components: GSoC/Mentoring ideas
> Reporter: Zhengqiang Duan
> Priority: Major
> Labels: Mentor, ShardingSphere, gsoc2023
>
> h2. Apache ShardingSphere
> Apache ShardingSphere is positioned as a Database Plus, and aims at building
> a standard layer and ecosystem above heterogeneous databases. It focuses on
> how to reuse existing databases and their respective upper layer, rather than
> creating a new database. The goal is to minimize or eliminate the challenges
> caused by underlying databases fragmentation.
> {*}Page{*}:
> [https://shardingsphere.apache.org|https://shardingsphere.apache.org/]
> {*}Github{*}: [https://github.com/apache/shardingsphere]
> h2. Background
> The ShardingSphere SQL federation engine provides support for complex SQL
> statements, and it can well support cross-database join queries, subqueries,
> aggregation queries and other statements. An important part of SQL federation
> engine is to convert the SQL statement parsed by ShardingSphere into SqlNode,
> so that Calcite can be used to implement SQL optimization and federated query.
> h2. Task
> This issue is to solve the MySQL exception that occurs during
> SQLNodeConverterEngine conversion. The specific case list is as follows.
> * select_char
> * select_extract
> * select_from_dual
> * select_from_with_table
> * select_group_by_with_having_and_window
> * select_not_between_with_single_table
> * select_not_in_with_single_table
> * select_substring
> * select_trim
> * select_weight_string
> * select_where_with_bit_expr_with_ampersand
> * select_where_with_bit_expr_with_caret
> * select_where_with_bit_expr_with_div
> * select_where_with_bit_expr_with_minus_interval
> * select_where_with_bit_expr_with_mod
> * select_where_with_bit_expr_with_mod_sign
> * select_where_with_bit_expr_with_plus_interval
> * select_where_with_bit_expr_with_signed_left_shift
> * select_where_with_bit_expr_with_signed_right_shift
> * select_where_with_bit_expr_with_vertical_bar
> * select_where_with_boolean_primary_with_comparison_subquery
> * select_where_with_boolean_primary_with_is
> * select_where_with_boolean_primary_with_is_not
> * select_where_with_boolean_primary_with_null_safe
> * select_where_with_expr_with_and_sign
> * select_where_with_expr_with_is
> * select_where_with_expr_with_is_not
> * select_where_with_expr_with_not
> * select_where_with_expr_with_not_sign
> * select_where_with_expr_with_or_sign
> * select_where_with_expr_with_xor
> * select_where_with_predicate_with_in_subquery
> * select_where_with_predicate_with_regexp
> * select_where_with_predicate_with_sounds_like
> * select_where_with_simple_expr_with_collate
> * select_where_with_simple_expr_with_match
> * select_where_with_simple_expr_with_not
> * select_where_with_simple_expr_with_odbc_escape_syntax
> * select_where_with_simple_expr_with_row
> * select_where_with_simple_expr_with_tilde
> * select_where_with_simple_expr_with_variable
> * select_window_function
> * select_with_assignment_operator
> * select_with_assignment_operator_and_keyword
> * select_with_case_expression
> * select_with_collate_with_marker
> * select_with_date_format_function
> * select_with_exists_sub_query_with_project
> * select_with_function_name
> * select_with_json_value_return_type
> * select_with_match_against
> * select_with_regexp
> * select_with_schema_name_in_column_projection
> * select_with_schema_name_in_shorthand_projection
> * select_with_spatial_function
> * select_with_trim_expr
> * select_with_trim_expr_from_expr
> You need to compare the difference between actual and expected, and then
> correct the logic in SQLNodeConverterEngine so that actual can be consistent
> with expected.
> After you make changes, remember to add case to SUPPORTED_SQL_CASE_IDS to
> ensure it can be tested.
>
> {*}Notice{*}, these issues can be a good example.
> [https://github.com/apache/shardingsphere/pull/14492|https://github.com/apache/shardingsphere/pull/15331]
> h2. Relevant Skills
>
> 1. Master JAVA language
> 2. Have a basic understanding of Antlr g4 file
> 3. Be familiar with MySQL and Calcite SqlNode
> h2. Targets files
>
> SQLNodeConverterEngineIT
> [https://github.com/apache/shardingsphere/blob/master/test/it/optimizer/src/test/java/org/apache/shardingsphere/test/it/optimize/SQLNodeConverterEngineIT.java]
>
> h3. Mentor
> Zhengqiang Duan, PMC of Apache ShardingSphere, duanzhengqi...@apache.org
> Chuxin Chen, Committer of Apache ShardingSphere,
> [tuichenchu...@apache.org|mailto:tuichenchu...@apache.org]
> Trista Pan, PMC of Apache ShardingSphere, panj...@apache.org
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