sql - 两个 SQL 查询的性能差异

Question

这是两个视图的简化版本：

viewA is select * from myTable;
viewB is select * from viewA;

直接从 viewA 选择和从 viewB 选择之间是否有任何性能差异，因为从 viewB 选择有另一层是 viewA？

Answer 1

CREATE OR REPLACE FORCE VIEW  "VIEWA" ("TITLE", "VALUE1", "VALUE2", "ID") AS 
  select "TITLE","VALUE1","VALUE2","ID" from dati
/
​CREATE OR REPLACE FORCE VIEW  "VIEWB" ("TITLE", "VALUE1", "VALUE2", "ID") AS 
  select "TITLE","VALUE1","VALUE2","ID" from viewa
/

​解释从 viewA 中选择 * 的计划

Operation           Options         Object  Rows    Time    Cost    Bytes   Filter          Access
                                                                            Predicates *    Predicates
SELECT STATEMENT                            4       1       3       268      
TABLE ACCESS        STORAGE FULL    DATI    4       1       3       268      

解释从 viewB 中选择 * 的计划

Operation           Options         Object  Rows    Time    Cost    Bytes   Filter          Access
                                                                            Predicates *    Predicates
SELECT STATEMENT                            4       1       3       268      
TABLE ACCESS        STORAGE FULL    DATI    4       1       3       268

我的回答必须是：不，没有任何性能差异。