说明Explain

EXPLAIN [EXTENDED | CODEGEN] statement

提供有关 statement 的详细计划信息,而无需实际运行。Provide detailed plan information about statement without actually running it. 默认情况下,这只会输出有关物理计划的信息。By default this only outputs information about the physical plan. 不支持说明 DESCRIBE TABLEExplaining DESCRIBE TABLE is not supported.

EXTENDED

在分析和优化前后输出有关逻辑计划的信息。Output information about the logical plan before and after analysis and optimization.

CODEGEN

输出语句的生成代码(如果有)。Output the generated code for the statement, if any.