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MySQL Interview Questions and Answers

Ques 66. How To Enter Characters as HEX Numbers?

Ans. If you want to enter characters as HEX numbers, you can quote HEX numbers with single quotes and a prefix of (X), or just prefix HEX numbers with (0x). A HEX number string will be automatically converted into a character string, if the expression context is a string. Here are some good examples:

SELECT X'313233' FROM DUAL;
123

SELECT 0x414243 FROM DUAL;
ABC

SELECT 0x46594963656E7465722E636F6D FROM DUAL; WithoutBook.com

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Ques 67. How To Enter Numeric Values as HEX Numbers?
Ans. If you want to enter numeric values as HEX numbers, you can quote HEX numbers with single quotes and a prefix of (X), or just prefix HEX numbers with (0x). A HEX number string will be automatically converted into a numeric value, if the expression context is a numeric value. Here are some good examples:

SELECT X'10' + 16 FROM DUAL;
32

SELECT 0x1000 + 0 FROM DUAL;
4096
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Ques 68. How To Enter Binary Numbers in SQL Statements?
Ans. If you want to enter character strings or numeric values as binary numbers, you can quote binary numbers with single quotes and a prefix of (B), or just prefix binary numbers with (0b). Binary numbers will be automatically converted into character strings or numeric values based on the expression contexts. Here are some good examples:

SELECT B'010000010100001001000011' FROM DUAL;
ABC

SELECT 0b1000 + 0 FROM DUAL;
8
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Ques 69. What Are NULL Values?
Ans. NULL is a special value that represents no value. Here are basic rules about NULL values:

► NULL presents no value.
► NULL is not the same as an empty string ''.
► NULL is not the same as a zero value 0.
► NULL can be used as any data type.
► NULL should not be used in any comparison options.
► NULL has its own equality operator "IS".
► NULL has its own not-equality operator "IS NOT".
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Ques 70. What Happens If NULL Values Are Involved in Expressions?
Ans. If NULL values are used in expressions, the resulting values will be NULL values. In other words:

► Arithmetic expressions with NULL values result NULL values.
► Comparison expressions with NULL values result NULL values.
► Logical expressions with NULL values result NULL values.

The tutorial exercise shows you some interesting examples:

SELECT NULL + NULL FROM DUAL;
NULL

SELECT NULL + 7 FROM DUAL;
NULL

SELECT NULL * 7 FROM DUAL;
NULL

SELECT NULL = NULL FROM DUAL;
NULL

SELECT 0 < NULL FROM DUAL;
NULL

SELECT '' > NULL FROM DUAL;
NULL

SELECT NULL AND TRUE FROM DUAL;
NULL

SELECT NULL OR TRUE FROM DUAL;
1
-- This is contradicting against the rules!
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