Question

我正在努力制作非常简单的东西，但我得出的结论是我的代码看起来非常难看，我很确定有一些方法可以提高代码性能和清晰度。

我怎样才能在Android SQLITE中使用SQL语句？

我有两张桌子：A和B. 在表格列d，p，u中。在表B列d，p，u中。列具有相同的名称。

我需要在每个表中找到最后添加的行，其中列p是某个值。并使用表A中列d和u的值更新表B中的列d和u。

final String selection = A.p + SQL_LIKE;
final String[] selectionArgs = new String[]{phone};
final String sortOrder = A.d + " DESC LIMIT 1";

final Cursor cursorA = getContentResolver().query(URI_A,
                null, selection, selectionArgs, sortOrder);

if (cursorA != null && cursorA.moveToFirst()) {

    final long dateTimeMillis = cursorA.getLong(cursorA.getColumnIndex(A.d));            

    final String selectionB = B.p + SQL_LIKE;
    final String[] selectionArgsB = new String[]{'%' + phone};
    final Cursor cursorB = getContentResolver().query(URI_A, null,
                        selectionB, selectionArgsB, A.d + " DESC LIMIT 1");

    if(cursorB != null && cursorB.moveToFirst()){

        final EntityB entityB = new EntityB().getUnitFromCursor(cursorB);

        final ContentValues contentValues = new ContentValues();
        contentValues.put(B.d, dateTimeMillis);
        contentValues.put(B.u, durationMillis);

        final String where = B._ID + SQL_ADD_VALUE;
                    final String[] whereArgs = new String[]{entityB.getId()};

        getContentResolver.update(URI_B, values, where, whereArgs)

        cursorB.close();
    }

callLogCursor.close();
}

问题：我如何改进我的代码，以便将来如果我需要相同的东西我不需要写那么多样板文件，它看起来更干净。我确信这个代码可以在一个SQL语句中更改 - 我认为这是解决此类问题的最佳解决方案。

Answer 1

UPDATE B
SET d = (SELECT d
         FROM A
         WHERE p LIKE ...
         ORDER BY d DESC
         LIMIT 1),
    u = (SELECT u
         FROM A
         WHERE p LIKE ...
         ORDER BY d DESC
         LIMIT 1)
WHERE ID = (SELECT ID
            FROM B
            WHERE p LIKE ...
            ORDER BY d DESC
            LIMIT 1);

如果A中的p可能没有B中特定EXISTS (SELECT * FROM A WHERE ...)的行，则必须在外部WHERE子句（public class ExtractionService { private int maxAmountOfThreads = 10; private int maxAmountOfMessagesPerThread = 1000; private int rowsReserved = 0; private int messagesProcessed = 0; private int messagesToProcess = 0; // value set later private List<String> ids = new ArrayList<String>(); private List<Thread> threads = new ArrayList<Thread>(); public void selectMessages(selectionAttributes) { final ExtractionService extractionService = this; ids = dao.selectIds(selectionAttributes) // selectionAttributes holds the configuration to only select the ids of the rows that match the users filter messagesToProcess = ids.size(); // can be for example 150'000 // If there are less rows returned than maxAmountOfThreads * maxAmountOfMessagesPerThread decrease the max amount of threads generated if((messagesToProcess / maxAmountOfThreads) <= maxAmountOfMessagesPerThread ) { maxAmountOfThreads = (int) (Math.ceil((float)messagesToProcess / (float)maxAmountOfMessagesPerThread )); } for(int i = 0; i < maxAmountOfThreads; i++) { //Create threads with start index (first messages to process for example starts at message 1001) and end index (last message to process in this thread for example 2001) int startRowIndex = messagesProcessed + rowsReserved; int lastRowIndex = ((startRowIndex + maxAmountOfMessagesPerThread < messagesToProcess) ? startRowIndex + maxAmountOfMessagesPerThread : messagesToProcess); threadArray.add(i, new Thread(new TransactionExtraction_Thread(startRowIndex, lastRowIndex, extractionService))); threadArray.get(i).start(); rowsReserved = rowsReserved + (lastRowIndex - startRowIndex); } boolean threadsAlive = true; while (threadsAlive) { threadsAlive = false; for (int i = 0; i < threadArray.size(); i++) { if (threadArray.get(i).isAlive()) { threadsAlive = true; break; } else if(!threadArray.get(i).isAlive() && (messagesProcessed + rowsReserved) < messagesToProcess) { int startRowIndex = messagesProcessed + rowsReserved; int lastRowIndex = ((startRowIndex + maxAmountOfMessagesPerThread < messagesToProcess) ? startRowIndex + maxAmountOfMessagesPerThread : messagesToProcess); threadArray.set(i, new Thread(new TransactionExtraction_Thread(startRowIndex, lastRowIndex, extractionService))); threadArray.get(i).start(); rowsReserved = rowsReserved + (lastRowIndex - startRowIndex); threadsAlive = true; } } } } }）中添加另一个过滤器

最小化和改进SQL语句的代码

1 个答案: