mysql和SQLserver的区别

时　间:2013-04-01 11:53:12
作　者:麥田   ID：11  城市：上海  QQ：3002789054
摘　要:mysql和SQLserver的区别
正　文:

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与SqlServer的差别实在太多，以上只是列出了我认为经常在写存储过程中会遇到的一些具体的差别之处。