社会分层
在履行合同过程中，发生不可抗力事件使一方或双方无法继续履行合同时，不能解除合同。
You dropped a schema of a user in an Oracle 10g by mistake. You decide to flash the database back to its previous state to restore the deleted schema. Which process writes the before images of the physical database blocks to the flashback database logs？（） LGWR。 DBWR。 MMON。 RVWR。
The EMP table has some discrepancy in data entry with a particular employee ID. You execute the query as shown in the Exhibit to retrieve all versions of the row that exist between two SCNs.View the Exhibit. Which two statements about the results of the query shown in the Exhibit are correct? （）(Choose two.) The LAST_SCN value in the first row is NULL, which means that the versions of the row still exist at SCN 6636300.。 The LAST_SCN value in the second row in NULL, which means that the version of the row still exists at SCN 6636300.。 The LAST_SCN value in the third row is 6636280, which means that the version of row exists above SCN 6636280.。 The LAST_SCN value in the second row is NULL, which means that the version of the row no longer exists because it was deleted.。
总投资2亿元以下且总库容在10亿m3以下的大中型和单位库容（每立方米）建设投资大于4元的小型病险水库除险加固工程，可直接编制（）。 初步设计。 可行性研究报告。 施工设计。 以上都不对。
What recommendations does the SQL Access Advisor provide for optimizing SQL queries？（）
