T-SQL和MySQL的一些常用語法的區別

本文將主要列出MySQL與SqlServer的SQL語句的一些常用語法的不同之處，且以常用的存儲過程的相關內容為主。
1. 標識符限定符 
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()函數，但意義不一樣
4. getdate()
SqlServer
getdate()
MySql
now()
5. newid()
SqlServer

newid()
MySql
uuid()

6. @@ROWCOUNT
SqlServer
@@ROWCOUNT
MySql
row_count()
注意：MySql的這個函數僅對於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 } ]

 

-- 若要定義語句塊，請使用控制流關鍵字 BEGIN 和 END。

 

MySql

IF search_condition THEN statement_list

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

END IF

注意：對於MySql來說，then, end if是必須的。類似的還有其它的流程控制語句，這里就不一一列出。

9. declare

其實，SqlServer和MySql都有這個語句，用於定義變量，但差別在於：在MySql中，DECLARE僅被用在BEGIN ... END復合語句里，並且必須在復合語句的開頭，在任何其它語句之前。這個要求在寫游標時，會感覺很BT.

10. 游標的寫法

 

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

-- 具體的處理邏輯

end if;

end while;

close _cursor_SN;

drop table _temp_SN;

注意：為了提高性能，通常在表變量上打開游標，不要直接在數據表上打開游標。

11. 分頁的處理

 

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;

當然，SqlServer中並不只有這一種寫法，只是這種寫法是比較常見而已。

 

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

 

以上只是列出了本人認為經常在寫存儲過程中會遇到的一些具體的差別之處。