如何从 MySQL 中的函数返回布尔值？
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How to return a boolean value from a function in MySQL?
提问by ratty
I have column aand column bin table emp. I'd like to retrieve values from those columns and find the difference between them with a function. The function would return truefor a 0 difference otherwise return false. I don't know how to return a value.
我有column a和column b在表中emp。我想从这些列中检索值并使用函数找到它们之间的差异。对于 0 差异，该函数将返回true，否则返回false。我不知道如何返回一个值。
Also, how do I store the retrieved values in a variable?
另外，如何将检索到的值存储在变量中？
回答by Mark Byers
MySQL doesn't really have booleans. TRUEand FALSEare aliases to 1 and 0, and the BOOLcolumn type is just an alias for TINYINT(1). All expressions that appear to give boolean results actually return 0 or 1.
MySQL 并没有真正的布尔值。TRUE和FALSE是 1 和 0BOOL的别名，列类型只是TINYINT(1). 所有看似给出布尔结果的表达式实际上都返回 0 或 1。
You could write your query as:
您可以将查询写为：
SELECT (a = b) AS a_equals_b
FROM emp
WHERE ...
回答by Salil
select a, b, if(a-b=0, true, false) as diff from emp;
回答by Flakron Bytyqi
go to
去
http://dev.mysql.com/doc/refman/5.1/en/numeric-type-overview.html
http://dev.mysql.com/doc/refman/5.1/en/numeric-type-overview.html
section
部分
BOOL, BOOLEAN
布尔值，布尔值
