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If the materialized slot is empty in inline view, the scanner will throw exception 'no materialized slot!'. When the outer query does not need any real columns of the inner query at all, such as the outer query only contains constant calculations, all slots in the inner query will not be materialized. For example: ``` select c1 from (select 'xx' c1, k1 from test) t1; ``` But this does not mean that the inner query (select 'xx' c1, k1 from test) does not need to be executed. Because the number of rows in the outer result needs to be determined by the number of rows in the inner query. In this case, the inner query scan node needs to add a column to ensure the correct result. At the same time it can avoid the scan node reporting errors.
# fe-common This module is used to store some common classes of other modules. # spark-dpp This module is Spark DPP program, used for Spark Load function. Depends: fe-common # fe-core This module is the main process module of FE. Depends: fe-common, spark-dpp