Which two statements will do an implicit conversion?

A. SELECT * FROM customers WHERE customer_id = 0001;
B. SELECT * FROM customers WHERE insert_date = Date '2019-01-01';
C. SELECT * FROM customers WHERE to_char(customer_id) = '0001';
D. SELECT * FROM customers WHERE customer_id = '0001';
E. SELECT * FROM customers WHERE insert_date = '01-JAN-19';

Answer: DE
Explanation:

D：customer_id 字段类型为 数值，引号为字符串，customer_id='0001'，字符串隐式转换为数字；
E：insert_date 字段类型为 日期，引号为字符串，insert_date='01-JAN-19' 字符串隐式转换为日期；