对于ORACLE PL/SQL标识符（Identifier）的有效长度是（）

当需要删除某个序列seq_customer_id，可以使用如下（）方式。

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select count（*） from student和select count（id） from student之间的区别是什么？

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在Oracle中，使用下列的语句产生序列： CREATE SEQUENCE id； Oracle服务器会预开辟内存并维持的序列值有（）个。

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在Oracle中，在执行SQL语句时，你不小心使用Update命令将所有的ID值设置成了11111，那么使用（）命令可以取消这一操作。

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Evaluate the SQL statement: SELECT LPAD (salary,10,*) FROM EMP WHERE EMP _ ID = 1001; If the employee with the EMP_ID 1001 has a salary of 17000, what is displayed?（）

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Evaluate the SQL statement: SELECT LPAD(salary,10,*) FROM EMP WHERE EMP_ID = 1001; If the employee with the EMP_ID 1001 has a salary of 17000, what is displayed?（）

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Examine the data of the EMPLOYEES table. EMPLOYEES (EMPLOYEE_ID is the primary key. MGR_ID is the ID of managers and refers to the EMPLOYEE_ID) Evaluate this SQL statement: What is its output?（）

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Evaluate this SQL statement: SELECT e.EMPLOYEE_ID,e.LAST_NAME,e.DEPARTMENT_ID, d.DEPARTMENT_NAME FROM EMPLOYEES e, DEPARTMENTS d WHERE e.DEPARTMENT_ID = d.DEPARTMENT_ID; In the statement, which capabilities of a SELECT statement are performed?（）

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Evaluate this SQL statement: SELECT e.EMPLOYEE_ID,e.LAST_NAME,e.DEPARTMENT_ID, d.DEPARTMENT_NAME FROM EMPLOYEES e, DEPARTMENTS d WHERE e.DEPARTMENT_ID = d.DEPARTMENT_ID; In the statement, which capabilities of a SELECT statement are performed?（）

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