Question

我正在尝试使用SQLite DB创建一个简单的Contacts应用程序。

我创建了自己的DBHelper类：

public class DBHelper {
public static final String KEY_NAME = "name";
public static final String KEY_ADDRESS = "address";
public static final String KEY_MOBILE = "mobile";
public static final String KEY_HOME = "home";
public static final String KEY_ROW_ID = "_id";
public static final String PROJECTION[] = {
        KEY_ROW_ID,
        KEY_NAME,
        KEY_ADDRESS,
        KEY_MOBILE,
        KEY_HOME
};
/* The table and database names */
private static final String TABLE_NAME = "mycontacts";
private static final String DATABASE_NAME = "contactDB";

    /*SQL code for creating the table*/

private static final String TABLE_CREATE=
        "create table "+ TABLE_NAME + "("+ KEY_ROW_ID
                +" integer primary key autoincrement,"+
                KEY_NAME +" text not null,"+
                KEY_ADDRESS + " text not null,"+
                KEY_MOBILE + " text,"+
                KEY_HOME + " text)";

private static final int DATABASE_VERSION = 1;

private SQLiteDatabase db;

public DBHelper(Context ctx){
    db = ctx.openOrCreateDatabase(DATABASE_NAME, SQLiteDatabase.CREATE_IF_NECESSARY, null);
    db.execSQL(TABLE_CREATE);
}
...
`enter code here`}

在类的构造函数中，正如您所看到的，我创建/打开数据库，之后我对其进行CREATE_TABLE查询以创建mycontacts表。

当我运行应用程序时（在Android Studio的模拟器上），我收到以下运行时错误：

Caused by: android.database.sqlite.SQLiteException: table mycontacts already exists (code 1): , while compiling: create table mycontacts(_id integer primary key autoincrement,name text not null,address text not null,mobile text,home text)

它表示已经创建了表，尽管我在创建db之后立即创建了创建查询。怎么可能？

Answer 1

将其写为“如果不存在则创建表格”

  private static final String TABLE_CREATE=
            "create table if not exists"+ TABLE_NAME + "("+ KEY_ROW_ID
                    +" integer primary key autoincrement,"+
                    KEY_NAME +" text not null,"+
                    KEY_ADDRESS + " text not null,"+
                    KEY_MOBILE + " text,"+
                    KEY_HOME + " text)";

在Android应用程序中的SQLite数据库中创建一个表

1 个答案: