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Commit ab18d1f4 authored by Owen Lin's avatar Owen Lin
Browse files

Fix SQLite limit issue. 

SQLLite limit is not only used to limit the returned number of data.
It can be used to do an offset query.

For example, "SELECT * FROM table LIMIT 100, 10", will return the
data of index in the range of [100, 100 + 10).

This change set enable this kind of useage.

This is also more efficient than use "cursor.moveToPosition()".
In my experiment, I query 1000 items in batch mode, i.e.,
get 20 items out of 1000 each time.

    Time of using LIMIT clause: 626ms
    Time of useing "cursor.moveToPosition()": 2062ms
parent d1874747

core/java/android/database/sqlite/SQLiteQueryBuilder.java

+8 −4
Original line number Diff line number Diff line
@@ -18,16 +18,15 @@ package android.database.sqlite; 


import android.database.Cursor;

import android.database.DatabaseUtils;

import android.database.sqlite.SQLiteDatabase;

import android.provider.BaseColumns;

import android.text.TextUtils;

import android.util.Config;

import android.util.Log;



import java.util.Iterator;

import java.util.Map;

import java.util.Set;

import java.util.Map.Entry;

import java.util.regex.Pattern;



/**

 * This is a convience class that helps build SQL queries to be sent to
@@ -36,10 +35,12 @@ import java.util.Map.Entry; 
public class SQLiteQueryBuilder

{

    private static final String TAG = "SQLiteQueryBuilder";

    private static final Pattern sLimitPattern =

            Pattern.compile("\\s*\\d+\\s*(,\\s*\\d+\\s*)?");



    private Map<String, String> mProjectionMap = null;

    private String mTables = "";

    private StringBuilder mWhereClause = new StringBuilder(64);

    private final StringBuilder mWhereClause = new StringBuilder(64);

    private boolean mDistinct;

    private SQLiteDatabase.CursorFactory mFactory;
@@ -169,6 +170,9 @@ public class SQLiteQueryBuilder 
            throw new IllegalArgumentException(

                    "HAVING clauses are only permitted when using a groupBy clause");

        }

        if (!TextUtils.isEmpty(limit) && !sLimitPattern.matcher(limit).matches()) {

            throw new IllegalArgumentException("invalid LIMIT clauses:" + limit);

        }



        StringBuilder query = new StringBuilder(120);
@@ -187,7 +191,7 @@ public class SQLiteQueryBuilder 
        appendClause(query, " GROUP BY ", groupBy);

        appendClause(query, " HAVING ", having);

        appendClause(query, " ORDER BY ", orderBy);

        appendClauseEscapeClause(query, " LIMIT ", limit);

        appendClause(query, " LIMIT ", limit);



        return query.toString();

    }