https://blog.csdn.net/qq_23833037/article/details/53170789
https://www.cnblogs.com/youring2/p/4916400.html
User-defined custom functions return scalar values like built-in functions , and can also return result sets as tabular variables .
The sql function must have a return value.
ps: The function is regarded as a function of processing some data. Because of the return value, a processed data is required in the code use.
You can directly call the function to process the data and return the data for the code to use.
Scalar function: Returns a scalar value.
table-valued function {inline table-valued function, multi-table-valued function}: returns a set of rows (ie, returns multiple values)
The difference between a scalar function and a table-valued function is whether the return is a scalar value (single number or single data) or a table value (multiple data)
1. Scalar function
create funetion function name (parameter)
return return value data type
[with {Encryption | Schemabinding }]
[as]
begin
SQL statement (must have return variable or value)
End
--Schemabinding : Bind the function to the object it refers to (Note: Once the function is bound, it cannot be deleted or modified unless the binding is deleted)
Test Data:
USE [Scratch] GO /****** Object: Table [dbo].[number] Script Date: 04/19/2018 17:01:31 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[number]( [number] [int] NULL, [name] [nchar](10) NULL ) ON [PRIMARY] GO
Insert data:
INSERT INTO number(number,name) VALUES(123,'a'), (222,'b'), (333,'c'), (323,'d')
example:
alter function SumRes(@sco nvarchar(20)) -- function name and parameters returns real -- returns the real value type -- real=float(24) as begin declare @sum real declare @code varchar(11) set @code = @sco + '%' select @sum = sum(number) from number where name like @code return @sum -- return value end
Quoting a custom function:
( The return value of the user-defined function can be placed in a local variable and assigned with set select exec)
declare @sum1 real,@sum2 real,@sum3 real
set @sum1 = dbo.SumRes('b')
select @sum2 = dbo.SumRes('b')
exec @sum3 = dbo.sumRes'b'
select @sum1 ,@sum2 ,@sum3
Example 2:
The following function returns age based on birthday:
create function dbo.calcAge(@birthday datetime) -- function name and parameters returns int -- return value type as begin declare @now datetime declare @age int set @now=getdate() set @age=YEAR(@now)-YEAR(@birthday) return @age -- return value end
print dbo.calcAge('2000-1-1')
Execute this script to create a function. After the creation is successful, let's call it to see the effect: Output: 15
2. Table-valued functions
a. Inline table-valued function
format:
create function function name (parameter)
returns table
[with{ Encryption | Schemabinding }]
as
return (a SQL statement)
example:
create function tabcmess(@code nvarchar(50)) returns table as return(select * from number where name = @code)
call and result:
b. Multi-sentence table-valued functions
Definition of multi-table-valued function: Contains multiple SQL statements, and at least one of them must assign values to table variables! ! !
Table variable format:
returns @variable name(dt) table(column definition | constraint definition)
Select, insert, update, delete can be performed on table variables,
but the result set of select into and insert statements are inserted from stored procedures.
Format:
create function function name (parameter)
return @dt table (column definition)
[with{Encryption | Schemabinding}]
as
begin
SQL statement
end
example:
create function tabcmess_mul(@code nvarchar(50)) returns @dt table(number int,name nchar(10)) as begin insert into @dt select number,name from number where name = @code return end
call and result:
3. Modify the custom function
alter function tabcmess_mul(@code nvarchar(50)) returns @dt table(number int,name nchar(10)) as begin insert into @dt select number,name from number where name = @code return end
4. Delete custom function
drop function tabcmess_mul