SQLite“如果不存在则添加列”

Question

如果需要检查表中是否已存在列，如果不存在则添加它。在应用程序中检查它是 NOT ，因为迁移会连续调用sql脚本/文件。如果我们向数据库添加一个新列，那么当应用程序（带有新版本）为startet时，该列应自动添加。

我有两个SQL Statements：

将列skiptime添加到recipes

ALTER TABLE recipes ADD COLUMN skiptime INTEGER NOT NULL DEFAULT 5;

检查Column是否已存在

SELECT * FROM sqlite_master WHERE type = 'table' AND name = 'recipes' AND sql LIKE '%skiptime%'

我得到的结果取决于column是否存在。现在我想结合这两个陈述。但我不知道如何。

添加了一些代码（请参阅注释）

RunMigrations()在Application启动时被调用一次。

ProviderInvariantName

可以是SQLite或PostgreSQL。

/// <summary>
/// Reads all ressource names from the assembly and saves those containing the db namespace in a private list
/// </summary>
private void _CacheDbRessources()
{
    _RessourcesNamespace = $"FooName.Data.{_ProviderInvariantName}";
    _RessourceNames = Assembly.GetExecutingAssembly().GetManifestResourceNames().Where(item => item.Contains(_RessourcesNamespace));
}

/// <summary>
/// Does the first-time setup for the database and runs migrations. 
/// </summary>
private void _RunMigrations()
{
    IEnumerable<string> migrations =
        _RessourceNames.Where(item => item.Contains("_Migrations"))
            .Select(s => s.Replace(_RessourcesNamespace + ".", ""))
            .OrderBy(item => item);

    if (migrations.Any())
        _Logger.Debug("Running database migrations...");

    using (DbConnection conn = GetConnection())
    {
        foreach (string item in migrations)
        {
            using (DbTransaction tran = conn.BeginTransaction())
            {
                _Logger.Debug("Executing query '{0}'...", item);
                using (DbCommand cmd = conn.CreateCommand(GetQueryResource(item), tran))
                {
                    int rows = cmd.ExecuteNonQuery();
                    _Logger.Debug($"{rows} rows where affected.");
                }

                tran.Commit();
            }
        }
    }
}

000_InitialCreate.sql（SQLite）

/* users */
CREATE TABLE IF NOT EXISTS "users" (
    "ident" INTEGER PRIMARY KEY AUTOINCREMENT,
    "user_name" TEXT NOT NULL UNIQUE,
    "real_name" TEXT,
    "password" TEXT NOT NULL,
    "userlevel" INTEGER NOT NULL DEFAULT 0,
    "enabled" INTEGER NOT NULL DEFAULT 1,
    "language" TEXT,
    "lock" TEXT
);

000_InitialCreate.sql（Postgres）

/* users */
CREATE TABLE IF NOT EXISTS "users" (
    "ident" SERIAL PRIMARY KEY,
    "user_name" TEXT NOT NULL UNIQUE,
    "real_name" TEXT,
    "password" TEXT NOT NULL,
    "userlevel" INTEGER NOT NULL DEFAULT 0,
    "enabled" INTEGER NOT NULL DEFAULT 1,
    "language" TEXT,
    "lock" TEXT
);