Question

我有一张这样的表：

1|EC7599A156DB1913AD9DE9A3A9540624B05683EC|Bar|World's Greatest|http://www.foo.com
2|EC7599A156DB1913AD9DE9A3A9540624B05683EC|Bar|World's Greatest|http://www.foo.com
3|EC7599A156DB1913AD9DE9A3A9540624B05683EC|Bar|World's Greatest|http://www.foo.com

该表的架构是：

CREATE TABLE IRChannels (
    ChannelId INTEGER PRIMARY KEY, 
    ChannelHash BLOB NOT NULL, 
    ChannelTitle TEXT NOT NULL, 
    ChannelDesc TEXT, 
    ChannelLink TEXT);

我尝试使用以下代码运行SELECT语句：

if (mReadDatabase != null) {
     String[]   columns = new String[]{COL_CHANNEL_ID};
     String     selection = COL_CHANNEL_HASH + "='" + hash + "'";
     try {
         Cursor cursor = mReadDatabase.query(
             TABLE_CHANNELS_NAME,      // Table Name 
             columns,                  // Channel ID
             selection,                // WHERE ChannelHash
             null,                     // = hash
             null,                     // Don't  Group
             null,                     // Don't filter by Groups
             null,                     // Use default Sort Order
             String.valueOf(1));       // LIMIT 1

         if (cursor.moveToFirst()) {
             return cursor;
         } else 
             return null;
    }

问题是我从未在返回的游标中看到任何数据。如果我在sqlite3 shell中尝试以下命令，我就能获得数据：

select channelid 
from irchannels 
where channelhash='EC7599A156DB1913AD9DE9A3A9540624B05683EC' 
limit 1

我能错过什么？

更新我尝试将我的代码更改为使用原始查询，但仍然没有区别：

if (mReadDatabase != null) {
    String        selection = COL_CHANNEL_HASH + "='" + hash + "'";
    final String  rawQuery = "SELECT " + COL_CHANNEL_ID +  
                " FROM " + TABLE_CHANNELS_NAME + " " + 
                " WHERE " + selection + 
                " LIMIT 1;";
        Cursor cursor = mReadDatabase.rawQuery(rawQuery, null);
}

Answer 1

试试这个，

String[]   columns = new String[]{COL_CHANNEL_ID};

Cursor cursor = mReadDatabase.query(
             TABLE_CHANNELS_NAME,      // Table Name 
             columns,                  // Channel ID
             "column_name=?",                // WHERE ChannelHash
             new String[]{hash},                     // = hash
             null,                     // Don't  Group
             null,                     // Don't filter by Groups
             null,                     // Use default Sort Order
             String.valueOf(1));       // LIMIT 1

Answer 2

某处我读过android需要id字段的特殊名称。您可以在示例中获取它：

public static final String COL_CHANNEL_ID = BaseColumns._ID;

在您的情况下，架构应该如下：

CREATE TABLE IRChannels (
    _id INTEGER PRIMARY KEY, 
    ChannelHash BLOB NOT NULL, 
    ChannelTitle TEXT NOT NULL, 
    ChannelDesc TEXT, 
    ChannelLink TEXT);

因为BaseColumns._ID通常等于“_id”

sqlite：SQLiteDase.query无法按预期工作

2 个答案: