private static ISqlSelect MakePagingTree_ReserveMethod(SqlSelect raw, int startRow, int endRow)
{
/*********************** 代码块解释 *********************************
* 源格式：
* SELECT *
* FROM A
* WHERE A.Id > 0
* ORDER BY A.NAME ASC
*
* 目标格式：
* SELECT * FROM
* (SELECT A.*, ROWNUM RN
* FROM A
* WHERE A.Id > 0 AND ROWNUM <= 20
* ORDER BY A.NAME ASC)
* WHERE RN >= 10
*
* 这种方法可能存在问题：
* 因为源 Sql 可能是：Select * From A Join B，这时表示结果集需要显示 A 和 B 的所有字段，
* 但是此方法会转换为：Select A.* From A Join B。比较麻烦，暂不处理
**********************************************************************/
var innerSelect = new SqlSelect
{
IsDistinct = raw.IsDistinct,
From = raw.From,
Where = AppendWhere(raw.Where, new SqlLiteral("ROWNUM <= " + endRow)),
OrderBy = raw.OrderBy
};
//内部的 Select 子句中，不能简单地使用 "*, ROWNUM"，而是需要使用 "A.*, ROWNUM"
var rawSelection = raw.Selection;
if (rawSelection == null)
{
//默认约定第一张表，就是
var table = new FirstTableFinder().Find(raw.From);
rawSelection = new SqlSelectAll
{
Table = table
};
}
innerSelect.Selection = new SqlNodeList
{
rawSelection,
new SqlLiteral(", ROWNUM RN")
};
var res = new SqlSelect
{
Selection = SqlSelectAll.Default,
From = new SqlSubSelect
{
Select = innerSelect
},
Where = new SqlLiteral("RN >= " + startRow)
};
return(res);
}
protected override SqlSelectAll VisitSqlSelectAll(SqlSelectAll sqlSelectStar)
{
if (sqlSelectStar.Table != null)
{
this.QuoteAppend(sqlSelectStar.Table.GetName());
_sql.Append(".*");
}
else
{
_sql.Append("*");
}
return(sqlSelectStar);
}
