Creating a SQL Server table from a C# datatable

Question

I have a DataTable that I manually created and loaded with data using C#.

What would be the most efficient way to create a table in SQL Server 2005 that uses the col

Answer 1

I know this question is rather old, but I just had something very similar that I needed to write. I took what I did and altered the examples provided by both Amin and rasputino and created an example that will output just the SQL. I added a few features and avoided concatenation to help improve upon a process that is inherently a poor performer.

/// 

/// Inspects a DataTable and return a SQL string that can be used to CREATE a TABLE in SQL Server.
/// 
/// System.Data.DataTable object to be inspected for building the SQL CREATE TABLE statement.
/// String of SQL
public static string GetCreateTableSql(DataTable table)
{
    StringBuilder sql = new StringBuilder();
    StringBuilder alterSql = new StringBuilder();

    sql.AppendFormat("CREATE TABLE [{0}] (", table.TableName);

    for (int i = 0; i < table.Columns.Count; i++)
    {
        bool isNumeric = false;
        bool usesColumnDefault = true;

        sql.AppendFormat("\n\t[{0}]", table.Columns[i].ColumnName);

        switch (table.Columns[i].DataType.ToString().ToUpper())
        {
            case "SYSTEM.INT16":
                sql.Append(" smallint");
                isNumeric = true;
                break;
            case "SYSTEM.INT32":
                sql.Append(" int");
                isNumeric = true;
                break;
            case "SYSTEM.INT64":
                sql.Append(" bigint");
                isNumeric = true;
                break;
            case "SYSTEM.DATETIME":
                sql.Append(" datetime");
                usesColumnDefault = false;
                break;
            case "SYSTEM.STRING":
                sql.AppendFormat(" nvarchar({0})", table.Columns[i].MaxLength);
                break;
            case "SYSTEM.SINGLE":
                sql.Append(" single");
                isNumeric = true;
                break;
            case "SYSTEM.DOUBLE":
                sql.Append(" double");
                isNumeric = true;
                break;
            case "SYSTEM.DECIMAL":
                sql.AppendFormat(" decimal(18, 6)");
                isNumeric = true;
                break;
            default:
                sql.AppendFormat(" nvarchar({0})", table.Columns[i].MaxLength);
                break;
        }

        if (table.Columns[i].AutoIncrement)
        {
            sql.AppendFormat(" IDENTITY({0},{1})", 
                table.Columns[i].AutoIncrementSeed, 
                table.Columns[i].AutoIncrementStep);
        }
        else
        {
            // DataColumns will add a blank DefaultValue for any AutoIncrement column. 
            // We only want to create an ALTER statement for those columns that are not set to AutoIncrement. 
            if (table.Columns[i].DefaultValue != null)
            {
                if (usesColumnDefault)
                {
                    if (isNumeric)
                    {
                        alterSql.AppendFormat("\nALTER TABLE {0} ADD CONSTRAINT [DF_{0}_{1}]  DEFAULT ({2}) FOR [{1}];", 
                            table.TableName, 
                            table.Columns[i].ColumnName, 
                            table.Columns[i].DefaultValue);
                    }
                    else
                    {
                        alterSql.AppendFormat("\nALTER TABLE {0} ADD CONSTRAINT [DF_{0}_{1}]  DEFAULT ('{2}') FOR [{1}];", 
                            table.TableName, 
                            table.Columns[i].ColumnName, 
                            table.Columns[i].DefaultValue);
                    }
                }
                else
                {
                    // Default values on Date columns, e.g., "DateTime.Now" will not translate to SQL.
                    // This inspects the caption for a simple XML string to see if there is a SQL compliant default value, e.g., "GETDATE()".
                    try
                    {
                        System.Xml.XmlDocument xml = new System.Xml.XmlDocument();

                        xml.LoadXml(table.Columns[i].Caption);

                        alterSql.AppendFormat("\nALTER TABLE {0} ADD CONSTRAINT [DF_{0}_{1}]  DEFAULT ({2}) FOR [{1}];", 
                            table.TableName, 
                            table.Columns[i].ColumnName, 
                            xml.GetElementsByTagName("defaultValue")[0].InnerText);
                    }
                    catch
                    {
                        // Handle
                    }
                }
            }
        }

        if (!table.Columns[i].AllowDBNull)
        {
            sql.Append(" NOT NULL");
        }

        sql.Append(",");
    }

    if (table.PrimaryKey.Length > 0)
    {
        StringBuilder primaryKeySql = new StringBuilder();

        primaryKeySql.AppendFormat("\n\tCONSTRAINT PK_{0} PRIMARY KEY (", table.TableName);

        for (int i = 0; i < table.PrimaryKey.Length; i++)
        {
            primaryKeySql.AppendFormat("{0},", table.PrimaryKey[i].ColumnName);
        }

        primaryKeySql.Remove(primaryKeySql.Length - 1, 1);
        primaryKeySql.Append(")");

        sql.Append(primaryKeySql);
    }
    else
    {
        sql.Remove(sql.Length - 1, 1);
    }

    sql.AppendFormat("\n);\n{0}", alterSql.ToString());

    return sql.ToString();
}

Here's a simple test to use this method and get the SQL:

DataTable table = new DataTable("Users");

table.Columns.Add(new DataColumn()
{
    ColumnName = "UserId",
    DataType = System.Type.GetType("System.Int32"),
    AutoIncrement = true,
    AllowDBNull = false,
    AutoIncrementSeed = 1,
    AutoIncrementStep = 1
});

table.Columns.Add(new DataColumn()
{
    ColumnName = "UserName",
    DataType = System.Type.GetType("System.String"),
    AllowDBNull = true,
    DefaultValue = String.Empty,
    MaxLength = 50
});

table.Columns.Add(new DataColumn()
{
    ColumnName = "LastUpdate",
    DataType = System.Type.GetType("System.DateTime"),
    AllowDBNull = false,
    DefaultValue = DateTime.Now, 
    Caption = "GETDATE()"
});

table.PrimaryKey = new DataColumn[] { table.Columns[0] };

string sql = DataHelper.GetCreateTableSql(table);

Console.WriteLine(sql);

And finally, the output:

CREATE TABLE [Users] (
    [UserId] int IDENTITY(0,1) NOT NULL,
    [UserName] nvarchar(50),
    [LastUpdate] datetime NOT NULL,
    CONSTRAINT PK_Users PRIMARY KEY (UserId)
);

ALTER TABLE Users ADD CONSTRAINT [DF_Users_UserName]  DEFAULT ('') FOR [UserName];
ALTER TABLE Users ADD CONSTRAINT [DF_Users_LastUpdate]  DEFAULT (GETDATE()) FOR[LastUpdate];

I agree with the original answer that states that data management isn't something that should be done haphazardly. It does indeed require a lot of thought to keep the DB running smoothly and allowing for maintainability in the future. But, there are times when a coding solution is necessary and I'm hoping this might help someone out.