插入到DB，如果不存在

Question

我试图插入行DB如果不通过电子邮件存在：

public boolean AddUserIfNotExist(String email, String password, String username) { 

    SQLiteDatabase db = m_helper.getWritableDatabase(); 


    //String Query = "INSERT OR IGNORE INTO USERS(email, password, username) 
    //values('" + email + "','" + password + "','" + username + "');"; 

    String Query = "INSERT INTO USERS(email, password, username) " + 
      "SELECT '" + email + "','" + password + "','" + username + "' " 
      + "WHERE NOT EXISTS(SELECT 1 FROM USERS WHERE email = '" + email + "');"; 

    Cursor cursor = db.rawQuery(Query, null); 

    if(cursor.getCount() <= 0) { 
     return false; 
    } 
    return true; 
} 

为什么它不工作？ cursor.getCount总是返回false。

Answer 1

INSERT语句不返回任何行，因此您不能使用rawQuery;对于INSERT，您必须改用execSQL。

如果要确定是否存在的记录或没有，只是做了单独（也使用的参数，以避免字符串格式化的问题）：

if (DatabaseUtils.queryNumEntries(db, "Users", 
            "email = ?", new String[] { email })) > 0) { 
    // probably UPDATE? 
    return true; 
} else { 
    db.execSQL("INSERT INTO Users(email, password, username) VALUES(?,?,?)", 
       new Object[] { email, password, username }); 
    return false; 
}