将
DISTINCTGROUPBYContentResolver现在我必须为每个特殊情况创建自定义 URI。
有更好的方法吗？
（我仍然以 1.5 作为最低公分母）
在查询 contentResolver 时，您可以做一些不错的 hack，使用：
String selection = Models.SOMETHING + "=" + something + ") GROUP BY (" + Models.TYPE;
如果您想将 DISTINCT 与 SELECT 多于一列一起使用，则需要使用 GROUP BY。
通过 ContentResolver.query 进行的迷你黑客使用：
Uri uri = Uri.parse("content://sms/inbox");
Cursor c = getContentResolver().query(uri,
new String[]{"DISTINCT address","body"}, //DISTINCT
"address IS NOT NULL) GROUP BY (address", //GROUP BY
null, null);
if(c.moveToFirst()){
do{
Log.v("from", "\""+c.getString(c.getColumnIndex("address"))+"\"");
Log.v("text", "\""+c.getString(c.getColumnIndex("body"))+"\"");
} while(c.moveToNext());
}
此代码从设备收件箱中为每个发件人选择最后一条短信。
注意：在 GROUP BY 之前我们总是需要至少写一个条件。
ContentResolver.query 方法中的结果 SQL 查询字符串将：
SELECT DISTINCT address, body FROM sms WHERE (type=1) AND (address IS NOT NULL) GROUP BY (address)
既然没有人来回答，我只想告诉你我是如何解决这个问题的。基本上，我会为每种情况创建自定义 URI，并在
selectionContentProvider#query这是一个简单的例子：
switch (URI_MATCHER.match(uri)) {
case TYPES:
table = TYPES_TABLE;
break;
case TYPES_DISTINCT:
return db.rawQuery("SELECT DISTINCT type FROM types", null);
default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
return db.query(table, null, selection, selectionArgs, null, null, null);
在您重写的
ContentProvider然后使用
SQLiteQueryBuildersetDistinct(boolean)@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder)
{
SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
boolean useDistinct = false;
switch (sUriMatcher.match(uri))
{
case YOUR_URI_DISTINCT:
useDistinct = true;
case YOUR_URI:
qb.setTables(YOUR_TABLE_NAME);
qb.setProjectionMap(sYourProjectionMap);
break;
default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
// If no sort order is specified use the default
String orderBy;
if (TextUtils.isEmpty(sortOrder))
{
orderBy = DEFAULT_SORT_ORDER;
}
else
{
orderBy = sortOrder;
}
// Get the database and run the query
SQLiteDatabase db = mDBHelper.getReadableDatabase();
// THIS IS THE IMPORTANT PART!
qb.setDistinct(useDistinct);
Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, orderBy);
if (c != null)
{
// Tell the cursor what uri to watch, so it knows when its source data changes
c.setNotificationUri(getContext().getContentResolver(), uri);
}
return c;
}
虽然我没有使用过Group By，但我在内容解析器查询中使用了Distinct。
Cursor cursor = contentResolver
.query(YOUR_URI,
new String[] {"Distinct "+ YOUR_COLUMN_NAME},
null,
null,
null);
在投影中添加 Distinct 关键字也对我有用，但是，只有当 unique 关键字是第一个参数时才有效：
String[] projection = new String[]{"DISTINCT " + DBConstants.COLUMN_UUID, ... };
在某些情况下，我们可以使用“distinct(COLUMN_NAME)”作为选择， 它工作完美。 但在某些情况下，会导致异常。
当它导致异常时，我将使用 HashSet 来存储列值....
// getting sender list from messages into spinner View
Spinner phoneListView = (Spinner) findViewById(R.id.phone_list);
Uri uri = Uri.parse("content://sms/inbox");
Cursor c = getContentResolver().query(uri, new String[]{"Distinct address"}, null, null, null);
List <String> list;
list= new ArrayList<String>();
list.clear();
int msgCount=c.getCount();
if(c.moveToFirst()) {
for(int ii=0; ii < msgCount; ii++) {
list.add(c.getString(c.getColumnIndexOrThrow("address")).toString());
c.moveToNext();
}
}
phoneListView.setAdapter(new ArrayAdapter<String>(BankActivity.this, android.R.layout.simple_dropdown_item_1line, list));
当您的投影中有多个列时，您应该这样做：
val uri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI
val projection = arrayOf(
"DISTINCT " + MediaStore.Images.Media.BUCKET_ID,
MediaStore.Images.Media.BUCKET_DISPLAY_NAME,
MediaStore.Images.Media.BUCKET_ID,
MediaStore.MediaColumns.DATA
)
val groupBySelection = " 1) GROUP BY (${MediaStore.Images.Media.BUCKET_ID}"
contentResolver.query(
uri,
projection,
null,
groupBySelection,
null,
null
)
带有右括号和内部数字“1”的groupBySelection是一个小技巧，但它工作得绝对没问题
我创建了一个使用 group by 和distinct 的实用方法。
以下是从 MMS 数据库中选择未见
thread_idquery(contentResolver= contentResolver,
select = arrayOf(Mms.THREAD_ID, "max(${Mms.DATE}) as date"),
from = Mms.CONTENT_URI,
where = "${Mms.SEEN} = 0",
groupBy = "1",
orderBy = "2 desc"
).use {
while (it?.moveToNext() == true){
val threadId = it.getInt(0)
val date = it.getLong(1)
}
}
fun query(
contentResolver: ContentResolver,
from: Uri,
select: Array<String>,
where: String? = null,
groupBy: Array<out String>? = null,
distinct: Boolean = false,
selectionArgs: Array<out String>? = null,
orderBy: String? = null,
): Cursor? {
val tmpSelect = select[0]
val localWhere =
if (groupBy == null) where
else "${where ?: "1"}) group by (${groupBy.joinToString()}"
if (distinct) {
select[0] = "distinct $tmpSelect"
}
val query = contentResolver.query(from, select, localWhere, selectionArgs, orderBy)
select[0] = tmpSelect
return query
}
也许获得不同的值更简单， 尝试在您想要投影表的列名之前添加 DISTINCT 单词
String[] projection = new String[]{
BaseColumns._ID,
"DISTINCT "+ Mediastore.anything.you.want
};
并将其用作内容解析器的查询方法的参数！
我希望能帮助你，因为前几天我也有同样的问题