mysql、sqlserver差别（一）

本文将主要列出MySql与SqlServer不同的地方，且以常用的存储过程的相关内容为主。

1. 标识符限定符

SqlServer	[]
MySql	``

2. 字符串相加

SqlServer	直接用 +
MySql	concat()

3. isnull()

SqlServer	isnull()
MySql	ifnull() 注意：MySql也有isnull()函数，但意义不一样

4. getdate()

SqlServer	getdate()
MySql	now()

5. newid()

SqlServer	newid()
MySql	uuid()

6. @@ROWCOUNT

SqlServer	@@ROWCOUNT
MySql	row_count() 注意：MySql的这个函数仅对于update, insert, delete有效

7. SCOPE_IDENTITY()

SqlServer	SCOPE_IDENTITY()
MySql	last_insert_id()

8. if ... else ...

SqlServer

IF Boolean_expression 
     { sql_statement | statement_block } 
[ ELSE 
     { sql_statement | statement_block } ] 
 
-- 若要定义语句块，请使用控制流关键字 BEGIN 和 END。

MySql

IF search_condition THEN statement_list
    [ELSEIF search_condition THEN statement_list] ...
    [ELSE statement_list]
END IF

注意：对于MySql来说，then, end if是必须的。类似的还有其它的流程控制语句，这里就不一一列出。

9. declare

其实，SqlServer和MySql都有这个语句，用于定义变量，但差别在于：在MySql中，DECLARE仅被用在BEGIN ... END复合语句里，并且必须在复合语句的开头，在任何其它语句之前。这个要求在写游标时，会感觉很BT.

10. 游标的写法

SqlServer

declare @tempShoppingCart table (ProductId int, Quantity int)
insert into @tempShoppingCart (ProductId, Quantity)
	select ProductId, Quantity from ShoppingCart where UserGuid = @UserGuid


declare @productId int
declare @quantity int
declare tempCartCursor cursor for 
		select ProductId, Quantity from @tempShoppingCart

open tempCartCursor
fetch next from tempCartCursor into @productId, @quantity
while  @@FETCH_STATUS = 0
begin
	update Product set SellCount = SellCount + @quantity	where productId = @productId

	fetch next from tempCartCursor into @productId, @quantity
end

close tempCartCursor
deallocate tempCartCursor

MySql

declare m_done int default 0;
declare m_sectionId int;
declare m_newsId int;

declare _cursor_SN cursor for select sectionid, newsid from _temp_SN;
declare continue handler for not found set m_done = 1;

create temporary table _temp_SN 
	select sectionid, newsid from SectionNews  group by sectionid, newsid having count(*) > 1;

open _cursor_SN;
while( m_done = 0 ) do
	fetch _cursor_SN into m_sectionId, m_newsId;
	
	if( m_done = 0 ) then 
		-- 具体的处理逻辑
	end if;
end while;
close _cursor_SN;
drop table _temp_SN;

注意：为了提高性能，通常在表变量上打开游标，不要直接在数据表上打开游标。

11. 分页的处理

SqlServer

create procedure GetProductByCategoryId( 
    @CategoryID int, 
    @PageIndex int = 0, 
    @PageSize int = 20, 
    @TotalRecords int output
) 
as
begin
     
declare @ResultTable table
( 
    RowIndex int, 
    ProductID int, 
    ProductName nvarchar(50), 
    CategoryID int, 
    Unit nvarchar(10), 
    UnitPrice money, 
    Quantity int
); 
     
insert into @ResultTable 
select row_number() over (order by ProductID asc) as RowIndex, 
       p.ProductID, p.ProductName, p.CategoryID, p.Unit, p.UnitPrice, p.Quantity 
from   Products as p 
where CategoryID = @CategoryID; 
       
select  @TotalRecords = count(*) from  @ResultTable; 
     
select * 
from   @ResultTable 
where  RowIndex > (@PageSize * @PageIndex) and RowIndex <= (@PageSize * (@PageIndex+1)); 
     
end;

当然，SqlServer中并不只有这一种写法，只是这种写法是比较常见而已。

MySql

create procedure GetProductsByCategoryId(
   in _categoryId int,
   in _pageIndex int,
   in _pageSize int,
   out _totalRecCount int
)
begin
 
   set @categoryId = _categoryId;
   set @startRow = _pageIndex * _pageSize;
   set @pageSize = _pageSize;
 
   prepare PageSql from 
	'select sql_calc_found_rows * from product  where categoryId = ? order by ProductId desc limit ?, ?';
   execute PageSql using @categoryId, @startRow, @pageSize;
   deallocate prepare PageSql;
   set _totalRecCount = found_rows();
 
end

mysql、sqlserver差别（一）

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