Question

当我在.sdf文件中只有一个表时，这段代码工作正常：

const string sdfPath = @"\Program Files\duckbilled\Platypus.sdf";
string dataSource = string.Format("Data Source={0}", sdfPath);

if (!File.Exists(sdfPath))
{
    using (var engine = new SqlCeEngine(dataSource))
    {
        engine.CreateDatabase();
    }
    using (var connection = new SqlCeConnection(dataSource))
    {
        connection.Open();
        using (var command = new SqlCeCommand())
        {
            command.Connection = connection;
            command.CommandText =
                "CREATE TABLE Platydudes (Id int NOT NULL, BillSize smallint NOT NULL, Description nvarchar(255)";
            command.ExecuteNonQuery();
        }
    }
}

...但现在我需要知道，不是数据库文件（Platypus.sdf）是否存在，而是是否存在特定的表（例如Platydudes）那个表/文件。有没有办法确定？

更新

查询中的“IF NOT EXISTS”子句导致运行时异常。这段代码：

using (var connection = new SqlCeConnection(dataSource))
{
    connection.Open();
    using (var command = new SqlCeCommand())
    {
        command.Connection = connection;
        command.CommandText = "IF NOT EXISTS( SELECT 1 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 'InventoryItems') " +
            "CREATE TABLE InventoryItems (Id nvarchar(50) NOT NULL, PackSize smallint NOT NULL, Description nvarchar(255), DeptDotSubdept numeric, UnitCost numeric, UnitList numeric, UPCCode nvarchar(50), UPCPackSize smallint, CRVId int);";
        command.ExecuteNonQuery();
    }
}

...导致抛出此异常：解析查询时出错。 [令牌行号= 1，令牌行偏移= 1，令牌错误= IF]

显然，查询解析器不需要“IF”业务。是否有另一种方法只创建表，如果它还不存在？或者我应该每次首先删除表格然后重新创建它？我应该这样做：

using (var connection = new SqlCeConnection(dataSource))
{
    connection.Open();
    using (var command = new SqlCeCommand())
    {
        command.Connection = connection;
        command.CommandText = "DELETE InventoryItems";
        command.ExecuteNonQuery();
    }
    using (var command = new SqlCeCommand())
    {
        command.Connection = connection;
        command.CommandText = "CREATE TABLE InventoryItems (Id nvarchar(50) NOT NULL, PackSize smallint NOT NULL, Description nvarchar(255), DeptDotSubdept numeric, UnitCost numeric, UnitList numeric, UPCCode nvarchar(50), UPCPackSize smallint, CRVId int);";
        command.ExecuteNonQuery();
    }
}

更新2

在第一次更新中回答我的上述问题：NOPE！如果我这样做，我会在第二次调用.ExecuteNonQuery（）时得到“指定的表已经存在”。

更新3

回应湿婆对我的回答的评论：

这（重用命令对象）失败的方式相同（“表已经存在”）：

using (var command = new SqlCeCommand())
{
    command.Connection = connection;
    command.CommandText = "DELETE InventoryItems";
    command.ExecuteNonQuery();
    command.CommandText = "CREATE TABLE InventoryItems (Id nvarchar(50) NOT NULL, PackSize smallint NOT NULL, Description nvarchar(255), DeptDotSubdept numeric, UnitCost numeric, UnitList numeric, UPCCode nvarchar(50), UPCPackSize smallint, CRVId int);";
    command.ExecuteNonQuery();
}

Answer 1

SQL Compact对SQL语句中的逻辑不太喜欢，因此Shiva的答案可能不会通过解析器。不过，他是在正确的路线上。您可以分两步完成：

以下是OpenNETCF ORM的SQL Compact实现中的TableExists方法：

public override bool TableExists(string tableName)
{
    var connection = GetConnection(true);
    try
    {
        using (var command = GetNewCommandObject())
        {
            command.Transaction = CurrentTransaction as SqlCeTransaction;
            command.Connection = connection;
            var sql = string.Format(
                    "SELECT COUNT(*) FROM information_schema.tables WHERE table_name = '{0}'", 
                     tableName);
            command.CommandText = sql;
            var count = Convert.ToInt32(command.ExecuteScalar());

            return (count > 0);
        }
    }
    finally
    {
        DoneWithConnection(connection, true);
    }
}

显然，你的情况并不完整，但很容易理解。 CurrentTransaction可能很容易为空。 GetNewCommandObject只返回一个新的SqlCeCommand实例。 GetConnection只是可以返回一个新的SqlCeConnection实例。 DoneWithConnection可能是NOP。基本上这些都是处理ORM支持过多支持商店的事实。您需要的信息内核是我传入的SQL以及我如何确定真/假的返回。

我（在编译器中未经测试）对结果方法的猜测是这样的：

public bool TableExists(SqlCeConnection connection, string tableName)
{
    using (var command = new SqlCeCommand())
    {
        command.Connection = connection;
        var sql = string.Format(
                "SELECT COUNT(*) FROM information_schema.tables WHERE table_name = '{0}'", 
                 tableName);
        command.CommandText = sql;
        var count = Convert.ToInt32(command.ExecuteScalar());
        return (count > 0);
    }
}

Answer 2

使用数据库助手：

var db = Database.Open("MyDatabase");
var sql = @"SELECT Count(*) FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 'MyTable'"
var count = db.QueryValue(sql);
if(count.Equals(1)){
    //table exists
}

Answer 3

如果要检查表是否存在，则必须使用TABLE_SCHEMA

IF (EXISTS (SELECT * 
             FROM INFORMATION_SCHEMA.TABLES 
             WHERE TABLE_SCHEMA = 'TheSchema' 
             AND  TABLE_NAME = 'TheTable'))
BEGIN
--Do Stuff
END

Answer 4

根据Shiva的回答，我会做这样的事情：

if (!File.Exists(sdfPath))
{
    using (var engine = new SqlCeEngine(dataSource))
    {
        engine.CreateDatabase();
    }
}

using (var connection = new SqlCeConnection(dataSource))
{
    connection.Open();
    using (var command = new SqlCeCommand())
    {
        command.Connection = connection;
        command.CommandText ="IF NOT EXISTS( SELECT 1 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 'Platydudes') " 
                           + "CREATE TABLE Platydudes (Id int NOT NULL, BillSize smallint NOT NULL, Description nvarchar(255) )";
        command.ExecuteNonQuery();
    }
}

...重复“使用（var connection = ...”部分根据需要为每个表格（Platypups，Platypops，＆amp; c）

更新

使用ctacke的代码，我现在有了这个：

public static void ConditionallyCreateTables()
{
    const string sdfPath = @"\Program Files\duckbilled\Platypus.sdf";
    string dataSource = string.Format("Data Source={0}", sdfPath);

    if (!File.Exists(sdfPath))
    {
        using (var engine = new SqlCeEngine(dataSource))
        {
            engine.CreateDatabase();
        }
    }
    using (var connection = new SqlCeConnection(dataSource))
    {
        connection.Open();
        using (var command = new SqlCeCommand())
        {
            command.Connection = connection;

            if (!TableExists(connection, "InventoryItems"))
            {
                command.CommandText = "CREATE TABLE InventoryItems (Id nvarchar(50) NOT NULL, PackSize smallint NOT NULL, Description nvarchar(255), DeptDotSubdept numeric, UnitCost numeric, UnitList numeric, UPCCode nvarchar(50), UPCPackSize smallint, CRVId int);";
                command.ExecuteNonQuery();
            }

            if (!TableExists(connection, "Departments"))
            {
                command.CommandText = "CREATE TABLE Departments (Id int NOT NULL, DeptNum int NOT NULL, DepartmentName nvarchar(255))";
                command.ExecuteNonQuery();
            }

            if (!TableExists(connection, "Subdepartments"))
            {
                command.CommandText = "CREATE TABLE Subdepartments (Id int NOT NULL, DeptId int NOT NULL, SubdeptId int NOT NULL, DepartmentName nvarchar(255))";
                command.ExecuteNonQuery();
            }

            if (!TableExists(connection, "Redemptions"))
            {
                command.CommandText = "CREATE TABLE Redemptions (Id int NOT NULL, RedemptionId nvarchar(50), RedemptionItemId nvarchar(50), RedemptionName nvarchar(255), RedemptionAmount numeric, RedemptionDept nvarchar(50), RedemptionSubdept nvarchar(50))";
                command.ExecuteNonQuery();
            }
        }
    }
}

更新2

我现在已将其更改为以下格式：

if (TableExists(connection, "InventoryItems"))
{
    command.CommandText = "DROP TABLE InventoryItems";
    command.ExecuteNonQuery();
}
command.CommandText = "CREATE TABLE InventoryItems (Id nvarchar(50) NOT NULL, PackSize smallint NOT NULL, Description nvarchar(255), DeptDotSubdept float, UnitCost float, UnitList float, UPCCode nvarchar(50), UPCPackSize smallint, CRVId int);";
command.ExecuteNonQuery();

如何以编程方式确定SQL Server CE数据库中是否存在表？

更新

更新2

更新3

4 个答案:

更新

更新2