Use of the IF condition statement in SQL

An IF expression

IF( expr1 , expr2 , expr3 )

The value of EXPR1 is TRUE, then the return value is EXPR2
The value of Expr1 is false, and the return value is EXPR3

As follows:

SELECTIF (true,1+ 1,1+2); -> 2select if (false,1 +1,1+< Span class= "Hljs-number" >2); -> 3select if (STRCMP ( "222"),  "unequal", -> not equal             

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So what's the use of this IF? As an example:
Find a book priced at 50, if it is a Java book, it should be marked as sold out
So how do you write the corresponding SQL statement?

select *,if(book_name=‘java‘,‘已卖完‘,‘有货‘) as product_status from book where price =50

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Ifnull-expression

IFNULL( expr1 , expr2 )

Returns EXPR1 if the value of EXPR1 is not true NULL , otherwise returns EXPR2, as follows:

SELECT IFNULL(NULL,"11");-> 11SELECT IFNULL("00","11");-> 00



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Use of the IF condition statement in SQL