bug: 'explain create table t as select ....' did create the table

[JackTan25]

Search before asking

• [X] I had searched in the issues and found no similar issues.

Version

936ffc9

What's Wrong?

the pipeline is not distributed, and explain sql will do "create table t4".

How to Reproduce?

mysql> explain pipeline  create table t4 as select * from target_table;
+--------------------------------------------------------------------------------------------+
| explain                                                                                    |
+--------------------------------------------------------------------------------------------+
| CommitSink × 1 processor                                                                   |
|   MutationAggregator × 1 processor                                                         |
|     TransformSerializeSegment × 1 processor                                                |
|       Merge (TransformSerializeBlock × 10 processors) to (TransformSerializeSegment × 1)   |
|         TransformSerializeBlock × 10 processors                                            |
|           BlockCompactTransform × 10 processors                                            |
|             CompoundBlockOperator(Project) × 10 processors                                 |
|               DeserializeDataTransform × 10 processors                                     |
|                 SyncReadParquetDataSource × 10 processors                                  |
+--------------------------------------------------------------------------------------------+
9 rows in set (0.10 sec)
Read 0 rows, 0.00 B in 0.047 sec., 0 rows/sec., 0.00 B/sec.

mysql> show tables;
+-------------------+
| Tables_in_default |
+-------------------+
| source_table      |
| t3                |
| t4                |
| target_table      |
| tmp               |
+-------------------+
5 rows in set (0.05 sec)
Read 5 rows, 1.00 KiB in 0.035 sec., 142.36 rows/sec., 28.56 KiB/sec.

Are you willing to submit PR?

• [X] Yes I am willing to submit a PR!

[dosubot[bot]]

Hey there, @JackTan25! I'm here to help you with any bugs, questions, or contributions you have for the repository. Let me know how I can assist you!

The issue you're encountering with the EXPLAIN CREATE TABLE AS SELECT statement creating the table is due to specific conditions in the codebase. When the EXPLAIN statement is used with ExplainKind::Plan and the plan is of type Plan::CreateTable, the code checks if the as_select field is present. If it is, the code proceeds to explain the query within the CREATE TABLE AS SELECT statement, which can inadvertently lead to the execution of the CREATE TABLE operation.

Here is the relevant code snippet:

Plan::CreateTable(plan) => match &plan.as_select {
    Some(box Plan::Query {
        s_expr,
        metadata,
        bind_context,
        formatted_ast,
        ..
    }) => {
        let mut res =
            vec![DataBlock::new_from_columns(vec![StringType::from_data(
                vec!["CreateTableAsSelect:", ""],
            )])];
        res.extend(
            self.explain_query(s_expr, metadata, bind_context, formatted_ast)
                .await?,
        );
        vec![DataBlock::concat(&res)?]
    }
    _ => self.explain_plan(&self.plan)?,
},

This code indicates that if the as_select field is present in the CreateTable plan, the explain_query method is called, which could lead to the execution of the CREATE TABLE operation ^[1].

Additionally, the test cases from tests/sqllogictests/suites/mode/standalone/explain/explain_ddl.test provide further evidence that the EXPLAIN statement for CREATE TABLE AS SELECT includes detailed query plan information, suggesting that the query is being processed in a way that could lead to the execution of the CREATE TABLE operation ^[2].

To address this issue, you may need to modify the handling of the EXPLAIN statement to ensure that it does not execute the CREATE TABLE operation. This could involve adding checks to prevent the execution or restructuring the code to separate the explanation logic from the execution logic.

To continue talking to Dosu, mention @dosu.