T SQL : String manipulation and DataTime extraction from string

SET @XmlFilename = 'JCA_RB_SP-20170531_152713.txt'

SELECT @IndexOfDash = CHARINDEX('-', @XmlFilename)

SELECT @BatchName = LEFT(@XmlFilename, CHARINDEX('-', @XmlFilename) - 1)

SELECT @BatchDateStringRaw = SUBSTRING(@XmlFilename, CHARINDEX('-', @XmlFilename) + 1, 15)

SELECT @BatchDateString = SUBSTRING(@BatchDateStringRaw, 1, 4) + '-' + SUBSTRING(@BatchDateStringRaw, 5, 2) + '-' + SUBSTRING(@BatchDateStringRaw, 7, 2)

+ ' ' + SUBSTRING(@BatchDateStringRaw, 10, 2) + ':' + SUBSTRING(@BatchDateStringRaw, 12, 2) + ':' + SUBSTRING(@BatchDateStringRaw, 14, 2)

SELECT

[@XmlFilename] = @XmlFilename,

[@IndexOfDash] = @IndexOfDash,

[@BatchName] = @BatchName,

[@BatchDateStringRaw] = @BatchDateStringRaw,

[@BatchDateString] = @BatchDateString,

CAST(@BatchDateString AS datetime)

,CAST(CAST(@BatchDateString AS datetime2) AS varchar(30))

,CAST(CAST(CAST(@BatchDateString AS datetime2) AS varchar(50)) AS datetime2)