Question

求ORACLE大神指导~主要是不懂TO_CHAR(number，'Not Available')是什么意思？把数字变成什么啊？

Using the CUSTOMERS table, you need to generate a report that shows an increase
in the credit limit by 15% for all customers. Customers whose credit limit has not
been entered should have the message "Not Available" displayed.
Which SQL statement would produce the required result?
A. SELECT NVL(cust_credit_limit, 'Not Available')*.15 "NEW CREDIT"
FROM customers;
B. SELECT NVL(cust_credit_limit*.15,'Not Available') "NEW CREDIT" FROM
customers;
C. SELECT TO_CHAR(NVL(cust_credit_limit*.15,'Not Available')) "NEW
CREDIT" FROM customers;
D. SELECT NVL(TO_CHAR(cust_credit_limit*.15),'Not Available') "NEW
CREDIT" FROM customers;
Answer: D

Answer 1

to_char就是把括号里面的内容变成字符，也就是跟后面的'Not Available'同一个类型。

追问

括号里的如果是数字呢？如何变成字符啊？求指教，谢谢

追答

只是数据库认为成字符，存储方式不一样。对你看起来说是一样的。举个例子。1，2，10，这三个数字，如果为数字类型那么在默认排序的时为1，2，10.如果是字符类则排序为1，10，2，
还有数字类1=01，字符类这二个就是不同的二个值， 查询语句如为数字类可以不加引号，字符的话就要加。。。