Databases - create databases, tables, functions, etc.

1、创建自定义函数

• 自定义函数分为：Scalar-valued functions or table-valued functions.
  • 标量值函数：如果 RETURNS 子句指定一种标量数据类型,则函数为标量值函数.
  • 表值函数：如果 RETURNS 子句指定 TABLE,Then the function is a table-valued function.
• There are two types of table-valued functions：内嵌表值函数（行内函数）or multi-statement functions
  • 如果 RETURNS 子句指定的 TABLE List without columns,Then the function is an inline table-valued function.
  • 如果 RETURNS 子句指定的 TABLE Types have columns and their data types,Then the function is a multi-statement table-valued function

1.1 函数语法：

Create function 函数名（参数）
Returns 返回值数据类型
[with {Encryption | Schemabinding }]
[as]
begin
SQL语句(必须有return 变量或值)
End

1.2 Scalar-valued function instance：

CREATE FUNCTION Foo(@ret int )  --传入了一个int类型的参数
RETURNS int       --Note that what is returned here is a data type
AS  
BEGIN 
    declare @n int
    set @n = 3
    return @n* @ret
END

1.3 Inline table-valued function syntax：

create function 函数名（参数）
returns table
[with {Encryption | Schemabinding }]
as
return(一条SQL语句)

eg

create function GetUser(@name varchar(10))
returns table
as
return select * from userInfo where userName=@name
调用：
select * from getuser('admin')

1.4 Multi-statement table-valued function syntax：

--Multi-sentence table-valued functions
   create function 函数名（参数）
   returns table variable nametable (Table variable definitions)
   [with {Encryption | Schemabinding }]
as
   begin
    SQL语句
   end
--A multi-sentence table-valued function contains multiple entriesSQL语句,At least one of the table variables is filled with data values

eg

create function GetInfo(@name varchar(20))
returns @cTable table(UserName varchar(10),UserPwd varchar(10))
as
begin
　　insert into @cTable
　　select userName,userPass from userinfo where username=@name
return   --The last statement in a function must be a return statement.
end
--调用
select * from GetInfo('admin')
------------
UserName UserPwd
admin     amin