我正在从我的数据库中复制数据，我如何知道首先从哪些表中复制以避免引用错误？

Question

我有一个数据库模式，其中有许多表和表之间的关系 - 你知道，标准 SQL 数据库设置。

我想生成 insert 语句来 "copy" 从一个数据库到另一个具有相同架构的数据，但是 none 的数据。

问题是，如果我以任何顺序执行此操作，它可能无法正常工作，因为先插入的数据可能取决于稍后才编写脚本的数据。

如何对 insert 语句进行排序，以便数据依赖项的顺序正确？

Answer 1

您想要的类型称为 topological sort. This orders elements (in your case, tables) so that depending elements come after dependency elements. One common technique to perform this kind of sorting is to build a graph structure and apply the sorting algorithm on it. Many frameworks have libraries which build graphs and have algorithms to perform the topological sort for you (.Net, Java, Python, C++)。

您将面临的一个问题是您的表是否具有循环关系。例如：

    [a] --> [b] --> [a]

这个循环阻止了图的拓扑排序，除非你知道 [a] 中的 none 个实体引用 [b] 中的实体，而后者又引用相同的实体[a] 中的实体，您无法确定是否会避免引用冲突。

这是 C# 中的示例脚本（使用 LinqPad) which queries the relationships in a database schema, uses Quickgraph 构建图形，然后对其进行拓扑排序并列出排序的表格（您可以从中构建 insert 语句），或列表如果无法按拓扑排序，则具有依赖循环的表：

http://share.linqpad.net/47qds2.linq

void Main()
{
    var targetDb = "MyDb";

    var relationSql = @"SELECT pk.TABLE_NAME as PrimaryKeyTable,
                            fk.TABLE_NAME as ForeignKeyRefTable
                        FROM
                            INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS r
                            INNER JOIN 
                                INFORMATION_SCHEMA.TABLE_CONSTRAINTS fk
                            ON
                                fk.CONSTRAINT_NAME = r.CONSTRAINT_NAME
                            INNER JOIN 
                                INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk
                            ON
                                pk.CONSTRAINT_NAME = r.UNIQUE_CONSTRAINT_NAME

                        ORDER BY
                        ForeignKeyRefTable";
    var tableSql = @"select t.[object_id] as TableId, t.[name] as TableName, c.[name] as ColName
                    from sys.tables t
                        inner join sys.columns c
                        on t.object_id = c.object_id";

    using(var conn = new SqlConnection(String.Format(@"Data Source=(localdb)\v11.0;Initial Catalog={0}", targetDb)))
    {
        var tables = conn.Query<Table>(tableSql);
        var relations = conn.Query<Relation>(relationSql);
        var relationGraph = new QuickGraph.AdjacencyGraph<String, Edge<String>>();
        relationGraph.AddVertexRange(tables.Select(t => t.TableName));
        var relationEdges = from r in relations
                            where r.ForeignKeyRefTable != r.PrimaryKeyTable
                            select new QuickGraph.Edge<String>(r.PrimaryKeyTable, r.ForeignKeyRefTable);
        relationGraph.AddEdgeRange(relationEdges);

        // The graph can be topologically sorted only if it is acyclic
        if (relationGraph.IsDirectedAcyclicGraph())
        {
            var inRelationOrder = relationGraph.TopologicalSort();
            inRelationOrder.Dump("Sorted Tables");
        }
        else
        {
            var connected = AlgorithmExtensions.CondensateStronglyConnected<String, Edge<String>, AdjacencyGraph<String, Edge<String>>>(relationGraph);
            var cycles = from v in connected.Vertices
                        where v.VertexCount > 1
                        select v.Vertices;
            cycles.Dump("Dependency Cycles");
        }
    }    
}

public class Table
{
    public Int32 TableId { get; set; }
    public String TableName { get; set; }
    public String ColName{ get; set; }
}

public class Relation
{
    public String PrimaryKeyTable { get; set; }
    public String ForeignKeyRefTable { get; set; }
}

我正在从我的数据库中复制数据，我如何知道首先从哪些表中复制以避免引用错误？

I'm copying data from my database, how do I know which tables to copy from first to avoid reference errors?

sql

database

insert

sql-insert