/// <summary>
        /// 解析 SELECT 命令
        /// </summary>
        /// <param name="tree">查询语义</param>
        /// <param name="indent">缩进</param>
        /// <param name="isOutermost">是否是最外层查询</param>
        /// <param name="context">解析SQL命令上下文</param>
        /// <returns></returns>
        protected override DbRawCommand TranslateSelectCommand(DbQuerySelectTree tree, int indent, bool isOutermost, ITranslateContext context)
        {
            var cmd = (DbSelectCommand)this.TranslateSelectCommandImpl(tree, indent, isOutermost, context);

            cmd.CombineFragments();
            if (isOutermost)
            {
                cmd.JoinFragment.Append(';');
            }
            return(cmd);
        }
 /// <summary>
 /// 初始化 <see cref="OracleDbQuerySelectTree"/> 类的新实例
 /// </summary>
 public OracleDbQuerySelectTree(DbQuerySelectTree source)
     : base()
 {
     this.Joins         = source.Joins;
     this.OrderBys      = source.OrderBys;
     this.Includes      = source.Includes;
     this.HasDistinct   = source.HasDistinct;
     this.HasAny        = source.HasAny;
     this.SelectHasMany = source.SelectHasMany;
     this.Skip          = source.Skip;
     this.Take          = source.Take;
     this.From          = source.From;
     this.Select        = source.Select;
     this.Wheres        = source.Wheres;
     this.Havings       = source.Havings;
     this.Aggregate     = source.Aggregate;
     this.GroupBy       = source.GroupBy;
     this.Subquery      = source.Subquery;
     this.Unions        = source.Unions;
 }
        // 解译 SELECT 语句
        private DbRawCommand TranslateSelectCommandImpl(DbQuerySelectTree tree, int indent, bool isOutermost, ITranslateContext context)
        {
            // 说明:
            // 1.OFFSET 前必须要有 'ORDER BY',即 'Skip' 子句前必须使用 'OrderBy' 子句
            // 2.在有聚合函数的<MAX,MIN...>情况下,如果有 'Distinct' 'GroupBy' 'Skip' 'Take' 子句,则需要使用嵌套查询
            // 3.'Any' 子句将翻译成 IF EXISTS...
            // 4.分组再分页时需要使用嵌套查询,此时子查询不需要 'OrderBy' 子句,但最外层则需要
            // 5.'Skip' 'Take' 子句视为语义结束符,在其之后的子句将使用嵌套查询
            // 6.导航属性中有 1:n 关系的,需要使用嵌套查询,否则分页查询会有问题
            // 8.如果只有 Skip 没有 Take,则使用 Row_Number() Over()分页语法,其它使用 LIMIT ## OFFSET 语法


            // 导航属性中有1:n关系,只统计主表
            // 例:AccountList = a.Client.AccountList,
            var subquery = tree.Subquery as DbQuerySelectTree;

            if (tree.SelectHasMany && subquery != null && subquery.Aggregate != null)
            {
                tree = subquery;
            }

            var srcDbExpressionType = context.CurrentExpressionType;
            var srcIsOutmost        = context.CurrentIsOutermost;

            if (srcDbExpressionType == null)
            {
                context.CurrentExpressionType = DbExpressionType.Select;
            }
            if (srcIsOutmost == null || !isOutermost)
            {
                context.CurrentIsOutermost = isOutermost;
            }

            bool useAggregate = tree.Aggregate != null;
            // 没有聚合函数或者使用 'Skip' 子句,则解析OrderBy
            // 导航属性如果使用嵌套,除非有 TOP 或者 OFFSET 子句,否则不能用ORDER BY
            // 第一层的表别名
            string alias       = context != null && !string.IsNullOrEmpty(context.AliasPrefix) ? (context.AliasPrefix + "0") : "t0";
            bool   useSubquery = tree.HasDistinct || tree.GroupBy != null || tree.Skip > 0 || tree.Take > 0;
            bool   useOrderBy  = (!useAggregate || tree.Skip > 0) && !tree.HasAny && (!tree.SelectHasMany || (tree.Skip > 0 || tree.Take > 0));

            AliasGenerator ag     = this.PrepareTableAlias(tree, context != null ? context.AliasPrefix : null);
            var            result = new DbSelectCommand(context, ag, tree.SelectHasMany);

            ISqlBuilder jf = result.JoinFragment;
            ISqlBuilder wf = result.WhereFragment;
            ISqlBuilder sf = null;

            jf.Indent = indent;

            #region 嵌套查询

            if (useAggregate && useSubquery)
            {
                // SELECT
                jf.Append("SELECT ");
                jf.AppendNewLine();

                // SELECT COUNT(1)
                var visitor = new AggregateExpressionVisitor(ag, jf, tree.GroupBy, alias);
                visitor.Visit(tree.Aggregate);
                result.AddNavMembers(visitor.NavMembers);

                // SELECT COUNT(1) FROM
                jf.AppendNewLine();
                jf.Append("FROM ( ");

                indent   += 1;
                jf.Indent = indent;
                context.CurrentIsOutermost = false;
            }

            #endregion

            #region  择子句

            // SELECT 子句
            if (jf.Indent > 0)
            {
                jf.AppendNewLine();
            }
            jf.Append("SELECT ");

            if (tree.HasAny)
            {
                jf.Append("CASE WHEN COUNT(1) = 1 THEN 1 ELSE 0 END FROM (");
                indent   += 1;
                jf.Indent = indent;
                jf.AppendNewLine();
                jf.Append("SELECT 1 ");
            }

            if (useAggregate && !useSubquery)
            {
                // 如果有聚合函数,并且不是嵌套的话,则直接使用SELECT <MAX,MIN...>,不需要解析选择的字段
                jf.AppendNewLine();
                var visitor_ = new AggregateExpressionVisitor(ag, jf, tree.GroupBy, null);
                visitor_.Visit(tree.Aggregate);
                result.AddNavMembers(visitor_.NavMembers);
            }
            else
            {
                // DISTINCT 子句
                if (tree.HasDistinct)
                {
                    jf.Append("DISTINCT ");
                }

                #region  择字段

                if (!tree.HasAny)
                {
                    // SELECT 范围
                    ColumnExpressionVisitor visitor = null;
                    if (tree.Skip > 0 && tree.Take == 0)
                    {
                        sf        = this.CreateSqlBuilder(context);
                        sf.Indent = jf.Indent + 1;

                        visitor = new ColumnExpressionVisitor(ag, sf, tree);
                        visitor.Visit(tree.Select);
                    }
                    else
                    {
                        visitor = new ColumnExpressionVisitor(ag, jf, tree);
                        visitor.Visit(tree.Select);
                    }

                    result.SelectedColumns    = visitor.SelectedColumns;
                    result.SelectedColumnText = visitor.SelectedColumnText;
                    result.SelectedNavs       = visitor.SelectedNavDescriptors;
                    result.AddNavMembers(visitor.NavMembers);

                    if (sf != null)
                    {
                        // 第一层嵌套
                        int index = 0;
                        jf.AppendNewLine();
                        foreach (var column in result.SelectedColumns)
                        {
                            jf.AppendMember(alias, column.Name);
                            jf.AppendAs(column.NewName);
                            index += 1;
                            if (index < result.SelectedColumns.Count)
                            {
                                jf.Append(',');
                                jf.AppendNewLine();
                            }
                        }

                        jf.AppendNewLine();
                        jf.Append("FROM(");

                        // 第二层嵌套
                        indent   += 1;
                        jf.Indent = indent;
                        jf.AppendNewLine();
                        jf.Append("SELECT");
                        jf.Append(sf);
                        jf.Append(',');
                        jf.AppendNewLine();

                        if (tree.OrderBys == null || tree.OrderBys.Count == 0)
                        {
                            throw new XFrameworkException("The method 'OrderBy' must be called before 'Skip'.");
                        }
                        jf.Append("ROW_NUMBER() OVER(");
                        var visitor3 = new OrderByExpressionVisitor(ag, jf, tree.GroupBy, null);
                        visitor3.Visit(tree.OrderBys, false);
                        result.AddNavMembers(visitor3.NavMembers);
                        jf.Append(") Row_Number0");
                    }
                }

                #endregion
            }

            #endregion

            #region 顺序解析

            // FROM 子句
            jf.AppendNewLine();
            jf.Append("FROM ");
            if (tree.Subquery != null)
            {
                // 子查询
                jf.Append("(");
                var cmd = this.TranslateSelectCommandImpl(tree.Subquery, indent + 1, false, context);
                jf.Append(cmd.CommandText);
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);
                jf.Append(' ');
            }
            else if (tree.FromSql != null)
            {
                if (tree.FromSql.DbContext == null)
                {
                    tree.FromSql.DbContext = context.DbContext;
                }
                DbRawSql rawSql = tree.FromSql;

                // 解析参数
                object[] args = null;
                if (rawSql.Parameters != null)
                {
                    args = rawSql.Parameters.Select(x => this.Constor.GetSqlValue(x, context)).ToArray();
                }
                string sql = rawSql.CommandText;
                if (args != null && args.Length > 0)
                {
                    sql = string.Format(sql, args);
                }

                // 子查询
                jf.Append('(');
                var cmd = new DbRawCommand(sql, context.Parameters, CommandType.Text);
                jf.Append(cmd.CommandText);
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);
                jf.Append(' ');
            }
            else
            {
                var typeRuntime = TypeRuntimeInfoCache.GetRuntimeInfo(tree.From);
                jf.AppendTable(typeRuntime.TableSchema, typeRuntime.TableName, typeRuntime.IsTemporary);
                jf.Append(' ');
                jf.Append(alias);
                jf.Append(' ');
            }

            // LEFT<INNER> JOIN 子句
            if (tree.Joins != null)
            {
                var visitor = new JoinExpressionVisitor(ag, jf);
                visitor.Visit(tree.Joins);
            }

            wf.Indent = jf.Indent;

            // WHERE 子句
            if (tree.Wheres != null)
            {
                var visitor = new WhereExpressionVisitor(ag, wf);
                visitor.Visit(tree.Wheres);
                result.AddNavMembers(visitor.NavMembers);
            }

            // GROUP BY 子句
            if (tree.GroupBy != null)
            {
                var visitor = new GroupByExpressionVisitor(ag, wf);
                visitor.Visit(tree.GroupBy);
                result.AddNavMembers(visitor.NavMembers);
            }

            // HAVING 子句
            if (tree.Havings != null)
            {
                var visitor = new HavingExpressionVisitor(ag, wf, tree.GroupBy);
                visitor.Visit(tree.Havings);
                result.AddNavMembers(visitor.NavMembers);
            }

            // ORDER 子句
            if (tree.OrderBys != null && tree.OrderBys.Count > 0 && useOrderBy)// && !groupByPaging)
            {
                var visitor = new OrderByExpressionVisitor(ag, wf, tree.GroupBy, null);
                visitor.Visit(tree.OrderBys);
                result.AddNavMembers(visitor.NavMembers);
            }

            #endregion

            #region 分页查询

            // LIMIT 子句可以被用于强制 SELECT 语句返回指定的记录数。
            // LIMIT 接受一个或两个数字参数。参数必须是一个整数常量。如果给定两个参数,第一个参数指定第一个返回记录行的偏移量,第二个参数指定返回记录行的最大数目。
            // 初始记录行的偏移量是 0(而不是 1): 为了与 PostgreSQL 兼容,MySQL 也支持句法: LIMIT # OFFSET #。
            // Limit n,-1 语法不支持,使用ROW_Number()语法代替

            if (tree.Take > 0)
            {
                wf.AppendNewLine().AppendFormat("LIMIT {0}", this.Constor.GetSqlValue(tree.Take, context));
                wf.AppendFormat(" OFFSET {0}", this.Constor.GetSqlValue(tree.Skip, context));
            }

            #endregion

            #region 嵌套查询

            if (useAggregate && useSubquery)
            {
                result.CombineFragments();
                indent   -= 1;
                jf.Indent = indent;
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);
            }

            #endregion

            #region 嵌套导航

            // TODO Include 从表,没分页,OrderBy 报错
            //if (tree.HasMany && subquery != null && subquery.OrderBys.Count > 0 && subquery.Aggregate == null && !(subquery.Skip > 0 || subquery.Take > 0))
            if (tree.SelectHasMany && subquery.Aggregate == null &&
                subquery != null && subquery.OrderBys != null && subquery.OrderBys.Count > 0 && !(subquery.Skip > 0 || subquery.Take > 0))
            {
                result.CombineFragments();
                var visitor = new OrderByExpressionVisitor(ag, jf, null, null);
                visitor.Visit(subquery.OrderBys);
            }

            #endregion

            #region 并集查询

            // UNION 子句
            if (tree.Unions != null && tree.Unions.Count > 0)
            {
                result.CombineFragments();
                for (int index = 0; index < tree.Unions.Count; index++)
                {
                    jf.AppendNewLine();
                    jf.Append("UNION ALL");
                    if (indent == 0)
                    {
                        jf.AppendNewLine();
                    }
                    DbRawCommand cmd = this.TranslateSelectCommandImpl(tree.Unions[index], indent, isOutermost, context);
                    jf.Append(cmd.CommandText);
                }
            }

            #endregion

            #region 分页查询

            if (sf != null)
            {
                // 合并 WHERE
                result.CombineFragments();

                indent   -= 1;
                jf.Indent = indent;
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);

                jf.AppendNewLine();
                jf.Append("WHERE ");
                if (tree.Skip > 0)
                {
                    jf.AppendMember(alias, "Row_Number0");
                    jf.Append(" > ");
                    jf.Append(this.Constor.GetSqlValue(tree.Skip, context));
                }
            }

            #endregion

            #region Any 子句

            // 'Any' 子句
            if (tree.HasAny)
            {
                // 产生 WHERE 子句
                result.CombineFragments();
                // 如果没有分页,则显式指定只查一笔记录
                if (tree.Take == 0 && tree.Skip == 0)
                {
                    jf.AppendNewLine();
                    jf.Append("LIMIT 0,1");
                }

                indent   -= 1;
                jf.Indent = indent;
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);
            }

            #endregion

            #region 还原状态

            context.CurrentExpressionType = srcDbExpressionType;
            context.CurrentIsOutermost    = srcIsOutmost;

            #endregion

            return(result);
        }
        /// <summary>
        /// 解析 SELECT 命令
        /// </summary>
        /// <param name="tree">查询语义</param>
        /// <param name="indent">缩进</param>
        /// <param name="isOutermost">是否是最外层查询</param>
        /// <param name="context">解析SQL命令上下文</param>
        /// <returns></returns>
        protected override DbRawCommand TranslateSelectCommand(DbQuerySelectTree tree, int indent, bool isOutermost, ITranslateContext context)
        {
            // 说明:
            // 1.OFFSET 前必须要有 'ORDER BY',即 'Skip' 子句前必须使用 'OrderBy' 子句
            // 2.在有聚合函数的<MAX,MIN...>情况下,如果有 'Distinct' 'GroupBy' 'Skip' 'Take' 子句,则需要使用嵌套查询
            // 3.'Any' 子句将翻译成 IF EXISTS...
            // 4.分组再分页时需要使用嵌套查询,此时子查询不需要 'OrderBy' 子句,但最外层则需要
            // 5.'Skip' 'Take' 子句视为语义结束符,在其之后的子句将使用嵌套查询
            // 6.导航属性中有 1:n 关系的,需要使用嵌套查询,否则分页查询会有问题
            // 8.如果有分页,则使用嵌套
            // 9.如果有分页还有OrderBy,则使用嵌套的嵌套

            // 导航属性中有1:n关系,只统计主表
            // 例:AccountList = a.Client.AccountList,
            var subquery = tree.Subquery as DbQuerySelectTree;

            if (tree.SelectHasMany && subquery != null && subquery.Aggregate != null)
            {
                tree = subquery;
            }

            var srcDbExpressionType = context.CurrentExpressionType;
            var srcIsOutmost        = context.CurrentIsOutermost;

            if (srcDbExpressionType == null)
            {
                context.CurrentExpressionType = DbExpressionType.Select;
            }
            if (srcIsOutmost == null || !isOutermost)
            {
                context.CurrentIsOutermost = isOutermost;
            }

            bool useAggregate = tree.Aggregate != null;
            // 没有聚合函数或者使用 'Skip' 子句,则解析OrderBy
            // 导航属性如果使用嵌套,除非有 TOP 或者 OFFSET 子句,否则不能用ORDER BY
            // 第一层的表别名
            string alias       = context != null && !string.IsNullOrEmpty(context.AliasPrefix) ? (context.AliasPrefix + "0") : "t0";
            bool   useSubquery = tree.HasDistinct || tree.GroupBy != null || tree.Skip > 0 || tree.Take > 0;
            bool   useOrderBy  = (!useAggregate || tree.Skip > 0) && !tree.HasAny && (!tree.SelectHasMany || (tree.Skip > 0 || tree.Take > 0));

            AliasGenerator ag     = this.PrepareTableAlias(tree, context != null ? context.AliasPrefix : null);
            var            result = new DbSelectCommand(context, ag, tree.SelectHasMany);

            ISqlBuilder jf = result.JoinFragment;
            ISqlBuilder wf = result.WhereFragment;

            (jf as OracleSqlBuilder).UseQuote = isOutermost;

            jf.Indent = indent;

            #region 嵌套查询

            if (useAggregate && useSubquery)
            {
                // SELECT
                jf.Append("SELECT ");
                jf.AppendNewLine();

                // SELECT COUNT(1)
                var visitor = new AggregateExpressionVisitor(ag, jf, tree.GroupBy, alias);
                visitor.Visit(tree.Aggregate);
                result.AddNavMembers(visitor.NavMembers);

                // SELECT COUNT(1) FROM
                jf.AppendNewLine();
                jf.Append("FROM ( ");

                indent   += 1;
                jf.Indent = indent;
                (jf as OracleSqlBuilder).UseQuote = false;
                context.CurrentIsOutermost        = false;
            }

            #endregion

            #region  择子句

            // SELECT 子句
            if (jf.Indent > 0)
            {
                jf.AppendNewLine();
            }
            jf.Append("SELECT ");

            if (tree.HasAny)
            {
                jf.Append("CASE WHEN COUNT(1) = 1 THEN 1 ELSE 0 END FROM (");
                indent   += 1;
                jf.Indent = indent;
                jf.AppendNewLine();
                jf.Append("SELECT 1 ");
            }

            if (useAggregate && !useSubquery)
            {
                // 如果有聚合函数,并且不是嵌套的话,则直接使用SELECT <MAX,MIN...>,不需要解析选择的字段
                jf.AppendNewLine();
                var visitor = new AggregateExpressionVisitor(ag, jf, tree.GroupBy, null);
                visitor.Visit(tree.Aggregate);
                result.AddNavMembers(visitor.NavMembers);
            }
            else
            {
                // DISTINCT 子句
                if (tree.HasDistinct)
                {
                    jf.Append("DISTINCT ");
                }

                #region  择字段

                if (!tree.HasAny)
                {
                    // SELECT 范围
                    ISqlBuilder sf = this.CreateSqlBuilder(context);
                    sf.Indent = jf.Indent + ((tree.Skip > 0 || tree.Take > 0) ? 2 : 0);
                    (sf as OracleSqlBuilder).UseQuote = (tree.Skip > 0 || tree.Take > 0) ? false : (jf as OracleSqlBuilder).UseQuote;

                    var visitor = new OracleColumnExpressionVisitor(ag, sf, tree);
                    visitor.Visit(tree.Select);

                    result.SelectedColumns    = visitor.SelectedColumns;
                    result.SelectedColumnText = visitor.SelectedColumnText;
                    result.SelectedNavs       = visitor.SelectedNavDescriptors;
                    result.AddNavMembers(visitor.NavMembers);

                    // 分页,产生两层嵌套
                    if (tree.Skip > 0 || tree.Take > 0)
                    {
                        // 第一层嵌套
                        int index = 0;
                        jf.AppendNewLine();
                        foreach (var column in result.SelectedColumns)
                        {
                            jf.AppendMember(alias, column.Name);
                            jf.AppendAs(column.NewName);
                            index += 1;
                            if (index < result.SelectedColumns.Count)
                            {
                                jf.Append(',');
                                jf.AppendNewLine();
                            }
                        }

                        jf.AppendNewLine();
                        jf.Append("FROM(");

                        // 第二层嵌套
                        indent     += 1;
                        isOutermost = false;
                        jf.Indent   = indent;
                        (jf as OracleSqlBuilder).UseQuote = isOutermost;
                        jf.AppendNewLine();

                        jf.Append("SELECT");
                        jf.AppendNewLine();

                        foreach (var column in result.SelectedColumns)
                        {
                            jf.AppendMember(alias, column.NewName);
                            jf.AppendAs(column.NewName);
                            jf.Append(',');
                            jf.AppendNewLine();
                        }
                        jf.Append("ROWNUM");
                        jf.AppendAs("Row_Number0");
                        jf.AppendNewLine();
                        jf.Append("FROM(");

                        // 第三层嵌套
                        indent   += 1;
                        jf.Indent = indent;
                        jf.AppendNewLine();
                        jf.Append("SELECT");
                    }

                    jf.Append(sf);
                }

                #endregion
            }

            #endregion

            #region 顺序解析

            // FROM 子句
            jf.AppendNewLine();
            jf.Append("FROM ");
            if (tree.Subquery != null)
            {
                // 子查询
                jf.Append('(');
                DbRawCommand cmd = this.TranslateSelectCommand(tree.Subquery, indent + 1, false, context);
                jf.Append(cmd.CommandText);
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);
                jf.Append(' ');
            }
            else if (tree.FromSql != null)
            {
                if (tree.FromSql.DbContext == null)
                {
                    tree.FromSql.DbContext = context.DbContext;
                }
                DbRawSql rawSql = tree.FromSql;

                // 解析参数
                object[] args = null;
                if (rawSql.Parameters != null)
                {
                    args = rawSql.Parameters.Select(x => this.Constor.GetSqlValue(x, context)).ToArray();
                }
                string sql = rawSql.CommandText;
                if (args != null && args.Length > 0)
                {
                    sql = string.Format(sql, args);
                }

                // 子查询
                jf.Append('(');
                var cmd = new DbRawCommand(sql, context.Parameters, CommandType.Text);
                jf.Append(cmd.CommandText);
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);
                jf.Append(' ');
            }
            else
            {
                var typeRuntime = TypeRuntimeInfoCache.GetRuntimeInfo(tree.From);
                jf.AppendTable(typeRuntime.TableSchema, typeRuntime.TableName, typeRuntime.IsTemporary);
                jf.Append(' ');
                jf.Append(alias);
                jf.Append(' ');
            }

            // LEFT<INNER> JOIN 子句
            if (tree.Joins != null)
            {
                var visitor = new JoinExpressionVisitor(ag, jf);
                visitor.Visit(tree.Joins);
            }

            wf.Indent = jf.Indent;

            // WHERE 子句
            if (tree.Wheres != null)
            {
                var visitor = new WhereExpressionVisitor(ag, wf);
                visitor.Visit(tree.Wheres);
                result.AddNavMembers(visitor.NavMembers);
            }

            // GROUP BY 子句
            if (tree.GroupBy != null)
            {
                var visitor = new GroupByExpressionVisitor(ag, wf);
                visitor.Visit(tree.GroupBy);
                result.AddNavMembers(visitor.NavMembers);
            }

            // HAVING 子句
            if (tree.Havings != null)
            {
                var visitor = new HavingExpressionVisitor(ag, wf, tree.GroupBy);
                visitor.Visit(tree.Havings);
                result.AddNavMembers(visitor.NavMembers);
            }

            // ORDER 子句
            if (tree.OrderBys != null && tree.OrderBys.Count > 0 && useOrderBy)
            {
                var visitor = new OrderByExpressionVisitor(ag, wf, tree.GroupBy, null);
                visitor.Visit(tree.OrderBys);
                result.AddNavMembers(visitor.NavMembers);
            }

            #endregion

            #region 嵌套查询

            if (useAggregate && useSubquery)
            {
                result.CombineFragments();
                indent   -= 1;
                jf.Indent = indent;
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);
            }

            #endregion

            #region 嵌套导航

            // TODO Include 从表,没分页,OrderBy 报错
            if (tree.SelectHasMany && subquery.Aggregate == null &&
                subquery != null && subquery.OrderBys != null && subquery.OrderBys.Count > 0 && !(subquery.Skip > 0 || subquery.Take > 0))
            {
                // OrderBy("a.CloudServer.CloudServerName");
                result.CombineFragments();
                var visitor = new OrderByExpressionVisitor(ag, jf, null, null);
                visitor.Visit(subquery.OrderBys);
            }

            #endregion

            #region 并集查询

            // UNION 子句
            if (tree.Unions != null && tree.Unions.Count > 0)
            {
                result.CombineFragments();
                for (int index = 0; index < tree.Unions.Count; index++)
                {
                    jf.AppendNewLine();
                    jf.Append("UNION ALL");
                    if (indent == 0)
                    {
                        jf.AppendNewLine();
                    }
                    DbRawCommand cmd2 = this.TranslateSelectCommand(tree.Unions[index], indent, isOutermost, context);
                    jf.Append(cmd2.CommandText);
                }
            }

            #endregion

            #region 分页查询

            if (tree.Take > 0 || tree.Skip > 0)
            {
                // 合并 WHERE
                result.CombineFragments();

                indent   -= 1;
                jf.Indent = indent;
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);

                indent   -= 1;
                jf.Indent = indent;
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);

                jf.AppendNewLine();
                jf.Append("WHERE ");
                if (tree.Skip > 0)
                {
                    jf.AppendMember(alias, "Row_Number0");
                    jf.Append(" > ");
                    jf.Append(this.Constor.GetSqlValue(tree.Skip, context));
                }
                if (tree.Take > 0)
                {
                    if (tree.Skip > 0)
                    {
                        jf.Append(" AND ");
                    }
                    jf.AppendMember(alias, "Row_Number0");
                    jf.Append(" <= ");
                    jf.Append(this.Constor.GetSqlValue((tree.Skip + tree.Take), context));
                }
            }

            #endregion

            #region Any子句

            // 'Any' 子句
            if (tree.HasAny)
            {
                // 产生 WHERE 子句
                result.CombineFragments();
                // 如果没有分页,则显式指定只查一笔记录
                if (tree.Take == 0 && tree.Skip == 0)
                {
                    if (tree.Wheres != null && tree.Wheres.Count > 0)
                    {
                        jf.Append(" AND ROWNUM <= 1");
                    }
                    else
                    {
                        jf.AppendNewLine();
                        jf.Append("WHERE  ROWNUM <= 1");
                    }
                }

                indent   -= 1;
                jf.Indent = indent;
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);
            }

            #endregion

            #region 还原状态

            context.CurrentExpressionType = srcDbExpressionType;
            context.CurrentIsOutermost    = srcIsOutmost;

            #endregion

            return(result);
        }
        /// <summary>
        /// 解析 SELECT 命令
        /// </summary>
        /// <param name="tree">查询语义</param>
        /// <param name="indent">缩进</param>
        /// <param name="isOutermost">是否外层查询,内层查询不需要结束符(;)</param>
        /// <param name="context">解析上下文</param>
        /// <returns></returns>
        protected override DbRawCommand TranslateSelectCommand(DbQuerySelectTree tree, int indent, bool isOutermost, ITranslateContext context)
        {
            // 说明:
            // 1.OFFSET 前必须要有 'ORDER BY',即 'Skip' 子句前必须使用 'OrderBy' 子句
            // 2.在有聚合函数的<MAX,MIN...>情况下,如果有 'Distinct' 'GroupBy' 'Skip' 'Take' 子句,则需要使用嵌套查询
            // 3.'Any' 子句将翻译成 IF EXISTS...
            // 4.分组再分页时需要使用嵌套查询,此时子查询不需要 'OrderBy' 子句,但最外层则需要
            // 5.'Skip' 'Take' 子句视为语义结束符,在其之后的子句将使用嵌套查询
            // 6.导航属性中有 1:n 关系的,需要使用嵌套查询,否则分页查询会有问题

            // 导航属性中有1:n关系,只统计主表
            // 例:AccountList = a.Client.AccountList,
            var subquery = tree.Subquery as DbQuerySelectTree;

            if (tree.SelectHasMany && subquery != null && subquery.Aggregate != null)
            {
                tree = subquery;
            }

            var srcDbExpressionType = context.CurrentExpressionType;
            var srcIsOutermost      = context.CurrentIsOutermost;

            if (srcDbExpressionType == null)
            {
                context.CurrentExpressionType = DbExpressionType.Select;
            }
            if (srcIsOutermost == null || !isOutermost)
            {
                context.CurrentIsOutermost = isOutermost;
            }

            bool useAggregate = tree.Aggregate != null;
            // 没有聚合函数或者使用 'Skip' 子句,则解析OrderBy
            // 导航属性如果使用嵌套,除非有 TOP 或者 OFFSET 子句,否则不能用ORDER BY
            // 第一层的表别名
            string alias       = context != null && !string.IsNullOrEmpty(context.AliasPrefix) ? (context.AliasPrefix + "0") : "t0";
            bool   useSubquery = tree.HasDistinct || tree.GroupBy != null || tree.Skip > 0 || tree.Take > 0;
            bool   useOrderBy  = (!useAggregate || tree.Skip > 0) && !tree.HasAny && (!tree.SelectHasMany || (tree.Skip > 0 || tree.Take > 0));

            AliasGenerator ag     = this.PrepareTableAlias(tree, context != null ? context.AliasPrefix : null);
            var            result = new SqlServerDbSelectCommand(context, ag, tree.SelectHasMany);

            ISqlBuilder jf = result.JoinFragment;
            ISqlBuilder wf = result.WhereFragment;

            jf.Indent = indent;

            #region 嵌套查询

            if (useAggregate && useSubquery)
            {
                // SELECT
                jf.Append("SELECT ");
                jf.AppendNewLine();

                // SELECT COUNT(1)
                var visitor = new AggregateExpressionVisitor(ag, jf, tree.GroupBy, alias);
                visitor.Visit(tree.Aggregate);
                result.AddNavMembers(visitor.NavMembers);

                // SELECT COUNT(1) FROM
                jf.AppendNewLine();
                jf.Append("FROM ( ");

                indent   += 1;
                jf.Indent = indent;
                context.CurrentIsOutermost = false;
            }

            #endregion 嵌套查询

            #region  择子句

            // SELECT 子句
            if (jf.Indent > 0)
            {
                jf.AppendNewLine();
            }
            if (tree.HasAny)
            {
                jf.Append("IF EXISTS(");
                indent   += 1;
                jf.Indent = indent;
                jf.AppendNewLine();
            }

            jf.Append("SELECT ");

            if (useAggregate && !useSubquery)
            {
                // 如果有聚合函数,并且不是嵌套的话,则直接使用SELECT <MAX,MIN...>,不需要解析选择的字段
                jf.AppendNewLine();
                var visitor = new AggregateExpressionVisitor(ag, jf, tree.GroupBy, null);
                visitor.Visit(tree.Aggregate);
                result.AddNavMembers(visitor.NavMembers);
            }
            else
            {
                // DISTINCT 子句
                if (tree.HasDistinct)
                {
                    jf.Append("DISTINCT ");
                }
                // TOP 子句
                if (tree.Take > 0 && tree.Skip == 0)
                {
                    jf.AppendFormat("TOP({0})", this.Constor.GetSqlValue(tree.Take, context));
                }
                // Any
                if (tree.HasAny)
                {
                    jf.Append("TOP 1 1");
                }

                #region 字段

                if (!tree.HasAny)
                {
                    // SELECT 范围
                    var visitor = new ColumnExpressionVisitor(ag, jf, tree);
                    visitor.Visit(tree.Select);

                    result.SelectedColumns    = visitor.SelectedColumns;
                    result.SelectedColumnText = visitor.SelectedColumnText;
                    result.SelectedNavs       = visitor.SelectedNavDescriptors;
                    result.AddNavMembers(visitor.NavMembers);
                }

                #endregion 字段
            }

            #endregion  择子句

            #region 顺序解析

            // FROM 子句
            jf.AppendNewLine();
            jf.Append("FROM ");
            if (tree.Subquery != null)
            {
                // 子查询
                jf.Append('(');
                DbRawCommand cmd = this.TranslateSelectCommand(tree.Subquery, indent + 1, false, context);
                jf.Append(cmd.CommandText);
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);
                jf.Append(' ');
            }
            else if (tree.FromSql != null)
            {
                if (tree.FromSql.DbContext == null)
                {
                    tree.FromSql.DbContext = context.DbContext;
                }
                DbRawSql rawSql = tree.FromSql;

                // 解析参数
                object[] args = null;
                if (rawSql.Parameters != null)
                {
                    args = rawSql.Parameters.Select(x => this.Constor.GetSqlValue(x, context)).ToArray();
                }
                string sql = rawSql.CommandText;
                if (args != null && args.Length > 0)
                {
                    sql = string.Format(sql, args);
                }

                // 子查询
                jf.Append('(');
                var cmd = new DbRawCommand(sql, context.Parameters, CommandType.Text);
                jf.Append(cmd.CommandText);
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);
                jf.Append(' ');
            }
            else
            {
                var typeRuntime = TypeRuntimeInfoCache.GetRuntimeInfo(tree.From);
                jf.AppendTable(typeRuntime.TableSchema, typeRuntime.TableName, typeRuntime.IsTemporary);
                jf.Append(' ');
                jf.Append(alias);
                jf.Append(' ');

                bool isNoLock = ((SqlServerDbContext)context.DbContext).NoLock;
                if (isNoLock && !string.IsNullOrEmpty(this._widthNoLock) && !typeRuntime.IsTemporary)
                {
                    jf.Append(this._widthNoLock);
                }
            }

            // LEFT<INNER> JOIN 子句
            if (tree.Joins != null)
            {
                var visitor = new SqlServerJoinExpressionVisitor(ag, jf);
                visitor.Visit(tree.Joins);
            }

            wf.Indent = jf.Indent;

            // WHERE 子句
            if (tree.Wheres != null)
            {
                var visitor = new WhereExpressionVisitor(ag, wf);
                visitor.Visit(tree.Wheres);
                result.AddNavMembers(visitor.NavMembers);
            }

            // GROUP BY 子句
            if (tree.GroupBy != null)
            {
                var visitor = new GroupByExpressionVisitor(ag, wf);
                visitor.Visit(tree.GroupBy);
                result.AddNavMembers(visitor.NavMembers);
            }

            // HAVING 子句
            if (tree.Havings != null)
            {
                var visitor = new HavingExpressionVisitor(ag, wf, tree.GroupBy);
                visitor.Visit(tree.Havings);
                result.AddNavMembers(visitor.NavMembers);
            }

            // ORDER 子句
            if (tree.OrderBys != null && tree.OrderBys.Count > 0 && useOrderBy)
            {
                var visitor = new OrderByExpressionVisitor(ag, wf, tree.GroupBy, null);
                visitor.Visit(tree.OrderBys);
                result.AddNavMembers(visitor.NavMembers);
            }

            #endregion

            #region 分页查询

            if (tree.Skip > 0)
            {
                if (tree.OrderBys == null || tree.OrderBys.Count == 0)
                {
                    throw new XFrameworkException("The method 'OrderBy' must be called before 'Skip'.");
                }
                wf.AppendNewLine();
                wf.Append("OFFSET ");
                wf.Append(this.Constor.GetSqlValue(tree.Skip, context));
                wf.Append(" ROWS");

                if (tree.Take > 0)
                {
                    wf.Append(" FETCH NEXT ");
                    wf.Append(this.Constor.GetSqlValue(tree.Take, context));
                    wf.Append(" ROWS ONLY ");
                }
            }

            #endregion 分页查询

            #region 嵌套查询

            if (useAggregate && useSubquery)
            {
                result.CombineFragments();
                indent   -= 1;
                jf.Indent = indent;
                jf.AppendNewLine();
                jf.Append(") ");
                jf.Append(alias);
                jf.Append(' ');
            }

            #endregion 嵌套查询

            #region 嵌套导航

            if (tree.SelectHasMany && subquery.Aggregate == null &&
                subquery != null && subquery.OrderBys != null && subquery.OrderBys.Count > 0 && !(subquery.Skip > 0 || subquery.Take > 0))
            {
                // TODO Include 从表,没分页,OrderBy 报错
                result.CombineFragments();
                var visitor = new OrderByExpressionVisitor(ag, jf, null, null);
                visitor.Visit(subquery.OrderBys);
            }

            #endregion 嵌套导航

            #region 并集查询

            // UNION 子句
            if (tree.Unions != null && tree.Unions.Count > 0)
            {
                result.CombineFragments();
                for (int index = 0; index < tree.Unions.Count; index++)
                {
                    jf.AppendNewLine();
                    jf.Append("UNION ALL");
                    if (indent == 0)
                    {
                        jf.AppendNewLine();
                    }
                    DbRawCommand cmd = this.TranslateSelectCommand(tree.Unions[index], indent, isOutermost, context);
                    jf.Append(cmd.CommandText);
                }
            }

            #endregion 并集查询

            #region Any 子句

            // 'Any' 子句
            if (tree.HasAny)
            {
                result.CombineFragments();
                indent   -= 1;
                jf.Indent = indent;
                jf.AppendNewLine();
                jf.Append(") SELECT 1 ELSE SELECT 0");
            }

            #endregion Any 子句

            #region 还原状态

            context.CurrentExpressionType = srcDbExpressionType;
            context.CurrentIsOutermost    = srcIsOutermost;

            #endregion

            return(result);
        }