如果項(xiàng)目中要用到數(shù)據(jù)庫(kù),鐵定要用到分頁(yè)排序。之前在做數(shù)據(jù)庫(kù)查詢優(yōu)化的時(shí)候,通宵寫了以下代碼,來拼接分頁(yè)排序的SQL語句
/// <summary>
/// 單表(視圖)獲取分頁(yè)SQL語句
/// </summary>
/// <param name="tableName">表名或視圖名</param>
/// <param name="key">唯一鍵</param>
/// <param name="fields">獲取的字段</param>
/// <param name="condition">查詢條件(不包含WHERE)</param>
/// <param name="collatingSequence">排序規(guī)則(不包含ORDER BY)</param>
/// <param name="pageSize">頁(yè)大小</param>
/// <param name="pageIndex">頁(yè)碼(從1開始)</param>
/// <returns>分頁(yè)SQL語句</returns>
public static string GetPagingSQL(
string tableName,
string key,
string fields,
string condition,
string collatingSequence,
int pageSize,
int pageIndex)
{
string whereClause = string.Empty;
if (!string.IsNullOrEmpty(condition))
{
whereClause = string.Format("WHERE {0}", condition);
}
if (string.IsNullOrEmpty(collatingSequence))
{
collatingSequence = string.Format("{0} ASC", key);
}
StringBuilder sbSql = new StringBuilder();
sbSql.AppendFormat("SELECT {0} ", PrependTableName(tableName, fields, ','));
sbSql.AppendFormat("FROM ( SELECT TOP {0} ", pageSize * pageIndex);
sbSql.AppendFormat(" [_RowNum_] = ROW_NUMBER() OVER ( ORDER BY {0} ), ", collatingSequence);
sbSql.AppendFormat(" {0} ", key);
sbSql.AppendFormat(" FROM {0} ", tableName);
sbSql.AppendFormat(" {0} ", whereClause);
sbSql.AppendFormat(" ) AS [_TempTable_] ");
sbSql.AppendFormat(" INNER JOIN {0} ON [_TempTable_].{1} = {0}.{1} ", tableName, key);
sbSql.AppendFormat("WHERE [_RowNum_] > {0} ", pageSize * (pageIndex - 1));
sbSql.AppendFormat("ORDER BY [_TempTable_].[_RowNum_] ASC ");
return sbSql.ToString();
}
/// <summary>
/// 給字段添加表名前綴
/// </summary>
/// <param name="tableName">表名</param>
/// <param name="fields">字段</param>
/// <param name="separator">標(biāo)識(shí)字段間的分隔符</param>
/// <returns></returns>
public static string PrependTableName(string tableName, string fields, char separator)
{
StringBuilder sbFields = new StringBuilder();
string[] fieldArr = fields.Trim(separator).Split(separator);
foreach (string str in fieldArr)
{
sbFields.AppendFormat("{0}.{1}{2}", tableName, str.Trim(), separator);
}
return sbFields.ToString().TrimEnd(separator);
}
假設(shè)有如下產(chǎn)品表:
CREATE TABLE [dbo].[Tbl_Product]
(
[ID] [int] IDENTITY(1, 1)
NOT NULL ,
[ProductId] [varchar](50) NOT NULL ,
[ProductName] [nvarchar](50) NOT NULL ,
[IsDeleted] [int] NOT NULL
CONSTRAINT [DF_Tbl_Product_IsDeleted] DEFAULT ( (0) ) ,
CONSTRAINT [PK_Tbl_Product] PRIMARY KEY CLUSTERED ( [ProductId] ASC )
WITH ( PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF,
IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON,
ALLOW_PAGE_LOCKS = ON ) ON [PRIMARY]
)
ON [PRIMARY]
Tbl_Product->ID(序號(hào),非空,自增)
Tbl_Product->ProductId(產(chǎn)品Id,主鍵)
Tbl_Product->ProductName(產(chǎn)品名稱,非空)
Tbl_Product->IsDeleted(虛擬刪除標(biāo)記,非空)
調(diào)用BasicFunction.GetPagingSQL("Tbl_Product", "ID", "ID,ProductId,ProductName", "IsDeleted=0", "ProductName ASC, ID DESC", 5, 5),BasicFunction為分頁(yè)排序方法所在的靜態(tài)類,生成的分頁(yè)排序SQL語句如下(已手動(dòng)調(diào)整了格式):
SELECT Tbl_Product.ID ,
Tbl_Product.ProductId ,
Tbl_Product.ProductName
FROM ( SELECT TOP 25
[_RowNum_] = ROW_NUMBER() OVER ( ORDER BY ProductName ASC, ID DESC ) ,
ID
FROM Tbl_Product
WHERE IsDeleted = 0
) AS [_TempTable_]
INNER JOIN Tbl_Product ON [_TempTable_].ID = Tbl_Product.ID
WHERE [_RowNum_] > 20
ORDER BY [_TempTable_].[_RowNum_] ASC
查詢的字段列表,去掉了不關(guān)心的字段(這里為IsDeleted,因?yàn)闂l件里面IsDeleted=0,查出來的產(chǎn)品都是沒被刪除的);
排序依據(jù),在調(diào)用該方法時(shí),應(yīng)盡量確保排序的依據(jù)可以唯一確定記錄在結(jié)果集中的位置(這里添加了輔助排序依據(jù),ID DESC,如果產(chǎn)品重名,添加的晚的排在前面);
性能優(yōu)化的一點(diǎn)兒建議:如果字段的值是計(jì)算出來的,如:總價(jià)=單價(jià)*數(shù)量,而此時(shí)需要總價(jià)大于多少的記錄,還得拿總價(jià)遞增或者遞減排序,如果不要臨時(shí)表,數(shù)據(jù)量大的時(shí)候,就等著買新電腦吧!你問我為什么要買新電腦,哦,因?yàn)槟銜?huì)把現(xiàn)在的電腦砸掉!O(∩_∩)O~
另外一點(diǎn)兒建議,使用ROW_NUMBER時(shí),切記一定要和“TOP n”一起使用,n等于int.MaxValue都比不加“TOP n”時(shí)要快。
最后,拜托哪位好心人士給測(cè)試下性能,拜托了,本人數(shù)據(jù)庫(kù)菜鳥,不太懂得數(shù)據(jù)庫(kù)的性能測(cè)試。
我只知道我對(duì)我寫的分頁(yè)排序還是很有信心的,(*^__^*) 嘻嘻!
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