数据库转换函数（包含在sql中的其他函数分类中）

CAST 和CONVERT

强制转换

CAST Syntax（句法）:CAST ( expression AS data_type [ ( length ) ] )

SELECT 9.5 AS Original, CAST(9.5 AS int) AS int, CAST(9.5 AS decimal(6,4)) AS decimal

   decimal(6,4) 6位有效数字，小数点后保留4位有效数字

转换

CAST Syntax（句法）:CONVERT ( data_type [ ( length ) ] , expression [ , style ] )

SELECT 9.5 AS Original, CONVERT(int, 9.5) AS int, CONVERT(decimal(6,4), 9.5) AS decimal

对expression中style各种类型的处理  

详细参考https://docs.microsoft.com/zh-cn/sql/t-sql/functions/cast-and-convert-transact-sql?view=sql-server-2017

隐式转换

详细参考https://docs.microsoft.com/zh-cn/sql/t-sql/functions/cast-and-convert-transact-sql?view=sql-server-2017