sqlserver isnull在mysql中怎么写

Posted 2023-04-16

参考技术A if(isnull(字段),默认值,字段)

MySql与SqlServer的一些常用用法的差别

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。

转自：http://www.cnblogs.com/fish-li/archive/2011/04/05/2006107.html