SQL (SQLServer) 中函数前的连字符有什么用

Question

我想知道 SQL 语法背后的逻辑是什么，在调用括号中的 SQL 函数之前包含连字符。

这里是 SQL:

IF (@StartDate > @EndDate)
BEGIN
    SET @EndDate = @StartDate
    SET @StartDate = @EndDate
END

DECLARE @nonworkingweekdays int

--now deal with public holidays
SELECT @nonworkingweekdays = count("Date") from 
(
    select distinct
    (
    CASE datepart(weekday,date)
            WHEN 1 THEN null --ignore sundays   
            WHEN 7 THEN null --ignore saturdays
            else "Date"
    END
    ) AS "date" 
    from publicholidays
) nonworkingweekdays 
WHERE 
"Date" is not null and 
"Date" between @StartDate and DATEADD(day, -1, @EndDate)

RETURN
    CASE WHEN @StartDate <= @EndDate
    THEN
        dbo.FullWeekDays(@StartDate, @EndDate) - @nonworkingweekdays
    ELSE
        -(dbo.FullWeekDays(@StartDate, @EndDate) - @nonworkingweekdays)
    END

我感到困惑的逻辑在 else 语句和此脚本底部的 return 语句中.

提前致谢:)

Answer 1

这是 TSQL Unary Negative Operator:

Returns the negative of the value of a numeric expression (a unary operator). Unary operators perform an operation on only one expression of any one of the data types of the numeric data type category.

Answer 2

连字符用于反转表达式值的符号，因为在这种情况下你有：

CASE WHEN @StartDate <= @EndDate
THEN
    dbo.FullWeekDays(@StartDate, @EndDate) - @nonworkingweekdays
ELSE
    -(dbo.FullWeekDays(@StartDate, @EndDate) - @nonworkingweekdays)
END

您正在 return计算日期之间的差异减去 nonworkingdays 变量。

这在逻辑上是最好的选择，因为你不能有 -1 天的差异，你总是需要一个正整数的差异。

务必设法区分 return 的类型（当 startdate 大于 enddate 时，反之亦然）

Answer 3

是一元否定运算符，所以和(0 - <expression>)一样。

也就是说，我猜这可以更简单地表示为：

RETURN ABS(dbo.FullWeekDays(@StartDate, @EndDate) - @nonworkingweekdays)

SQL (SQLServer) 中函数前的连字符有什么用

What is the use of the hyphen before a function in SQL (SQLServer)

sql

sql-server

function

unary-function