The first 118 Chapter SQL function REVERSE

Scalar string function , It returns a string in reverse character order .

The outline

REVERSE(string-expression)

Parameters

• string-expression - The expression of the string to be reversed . The expression can be a column name 、 String text 、 The result of a number or another scalar function , The basic data type can be expressed as any character type （ for example CHAR or VARCHAR）.

describe

REVERSE Returns a string expression with reversed character order . for example 'Hello World!' Return to '!dlroW olleH'. This is a simple string order reversal , No extra treatment .

The returned string is of data type VARCHAR, Independent of the data type of the input value . Convert numbers to canonical form , Numeric strings are not converted to canonical form until they are inverted .

Leading and trailing blanks are not affected by inversion .

reverse NULL Values can cause NULL.

Be careful ： because REVERSE Always return one VARCHAR character string , Therefore, some types of data will become invalid during inversion ：

• The reverse list is no longer a valid list , Cannot convert from storage format to display format .
• The reversal date is no longer a valid date , And cannot be converted from storage format to display format .

Example

The following example inverts Name field value . under these circumstances , This causes names to be sorted by middle initials ：

SELECT Name,REVERSE(Name) AS RevName
FROM Sample.Person
ORDER BY RevName

Please note that , because Name and RevName Just different representations of the same field , therefore ORDER BY RevName and ORDER BY RevName,Name Perform the same sort .

The following example inverts numbers and numeric strings ：

SELECT REVERSE(+007.10) AS RevNum,
       REVERSE('+007.10') AS RevNumStr
       
1.7	01.700+

The following embedded SQL Example inversion $DOUBLE Numbers ：

/// d ##class(PHA.TEST.SQLFunction).Reverse()
ClassMethod Reverse()
{
    
	s dnum = $DOUBLE(1.1)
	&sql(
		SELECT REVERSE(:dnum) INTO :drevnum
	)
	w dnum,!
	w drevnum,!
}

DHC-APP> d ##class(PHA.TEST.SQLFunction).Reverse()
1.1000000000000000888
8880000000000000001.1

The following example shows what happens when you reverse the list ：

SELECT FavoriteColors,REVERSE(FavoriteColors) AS RevColors
FROM Sample.Person

The following example shows what happens when the date is reversed ：

SELECT DOB,%INTERNAL(DOB) AS IntDOB,REVERSE(DOB) AS RevDOB
FROM Sample.Person