The difference between mysql and sqlserver (1)

This article will mainly list the differences between MySql and SqlServer, and mainly focus on the related content of commonly used stored procedures.

1. Identifier Qualifier

SqlServer	[]
MySql	``

2. String addition

SqlServer	use + directly
MySql	concat()

3. isnull()

SqlServer	isnull()
MySql	ifnull() Note: MySql also has isnull() function, but the meaning is different

4. getdate()

SqlServer	getdate()
MySql	now()

5. change ()

SqlServer	change ()
MySql	uuid()

6. @@ROWCOUNT

SqlServer	@@ROWCOUNT
MySql	row_count() Note: This function of MySql is only valid for update, insert, delete

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 } ]
 
-- To define a block of statements, use the control flow keywords BEGIN and END.

MySql

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

Note: For MySql, then, end if is required. There are other similar flow control statements, which are not listed here.

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

The difference between mysql and sqlserver (1)

Guess you like