C# 如何以编程方式确定SQL Server CE数据库中是否存在表？

当我的

.sdf

文件中只有一个表时，此代码运行良好：

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();
        }
    }
}

…但现在我需要知道的不是数据库文件（

Platypus.sdf

）是否存在，而是该表/文件中是否存在特定的表（例如

Platydudes

）。有办法确定吗

更新 查询中的“IF NOT EXISTS”子句导致运行时异常。此代码：

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();
    }
}

…导致引发此异常：分析查询时出错。[令牌行编号=1，令牌行偏移量=1，令牌出错=IF]

因此，查询解析器显然不需要“IF”业务。是否有其他方法仅在表不存在时创建该表？或者每次我都应该先删除表，然后重新创建它？瞧，我应该这样做吗：

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问题：不！如果这样做，则在第二次调用.ExecuteNonQuery（）时会得到“指定的表已经存在”

更新3 针对Shiva对我的回答的评论：

这（重用命令对象）以同样的方式失败（“表已存在”）：

---

如果要检查表是否存在，必须使用

Table\u SCHEMA

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

---

根据湿婆的回答，我会这样做：

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();
    }
}

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);
    }
}

…根据每个表（鸭嘴兽、鸭嘴兽和c）的需要重复“使用（var连接=…”部分

更新 使用ctacke的代码，我现在有：

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();

---

SQL Compact不太喜欢SQL语句中的逻辑，因此Shiva的答案可能无法通过解析器。不过，他的思路是正确的。您可以分两步完成：

以下是SQL Compact实现的

TableExists

方法：

显然，对于您的情况，它并不完整，但很容易理解。

CurrentTransaction

可以很容易地为空。

GetNewCommandObject

只返回一个新的

SqlCeCommand

实例。

GetConnection

只返回一个新的

SqlCeConnection

实例。DoneWithConnection可以是不，基本上，这些都是在处理ORM支持过多备份存储的事实。您需要的信息的核心是我传入的SQL以及我如何确定真/假返回

我（未经编译器测试）对结果方法的猜测如下：

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();
    }
}

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);
    }
}

使用数据库帮助器：

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
}

---

DELETE inventory items

不会删除表，它只会删除所有行。

DROP table inventory items

会删除表本身。哦，是的，我知道；大脑冻结！我想你应该在

connection.Open（）；

之前添加

var count=Convert.ToInt32（command.ExecuteScalar（））；

。我的工作就是这样的。