经典的100个C算法__（1）兔子问题

This article looks at using SQLite from the Android shell.

Table of Contents Where is SQLite? Code Listing 1. Contents of system/bin Where are the SQLite databases on an Android Device? Code Listing 2. The location of the notepad database Code Listing 3. The /data/data directory Starting the SQLite command line program Starting generically Code Listing 4. The SQLite commands available from the command line utility Opening a database Code Listing 5. Opening a specific database from SQLite command line Example Commands from the SQLite command line program Getting the list of tables Code Listing 6. List of tables Getting the schema of the tables Code Listing 7. Schema of tables SQL Queries Figure 1. Notes in the Note pad application Code Listing 8. Data from notes Code Listing 9. Creation of the notes table Related Articles

Where is SQLite?

SQLite is available on the Android device itself. The executable is in the /system/bin directory of the device. You can see that this directory contains the shell commands like ls, ps, etc., as well as sqlite3, dalvikvm, and dexdump utilities.

Code Listing 1. Contents of system/bin

# pwd

pwd

/system/bin

# ls -l

ls -l

-rwxr-xr-x root root 196 2008-02-29 01:09 am

-rwxr-xr-x root root 2342 2008-02-29 01:09 dumpstate

-rwxr-xr-x root root 208 2008-02-29 01:09 input

-rwxr-xr-x root root 212 2008-02-29 01:09 monkey

-rwxr-xr-x root root 196 2008-02-29 01:09 pm

…

lrwxr-xr-x root root 2008-02-29 01:16 mount -> toolbox

lrwxr-xr-x root root 2008-02-29 01:16 notify -> toolbox

-rwxr-xr-x root root 28032 2008-02-29 01:16 dexdump

-rwxr-xr-x root root 7100 2008-02-29 01:16 dumpsys

-rwxr-xr-x root root 7904 2008-02-29 01:16 mem_profiler

-rwxr-xr-x root root 6480 2008-02-29 01:16 service

-rwxr-xr-x root root 4320 2008-02-29 01:16 rild

-rwxr-xr-x root root 4928 2008-02-29 01:16 sdutil

-rwxr-xr-x root root 26488 2008-02-29 01:16 sqlite3

-rwxr-xr-x root root 4148 2008-02-29 01:16 dexopt

-rwxr-xr-x root root 4908 2008-02-29 01:16 dalvikvm

-rwsr-sr-x root root 3200 2008-02-29 01:16 surfaceflinger

-rwxr-xr-x root root 5420 2008-02-29 01:16 app_process

-rwxr-xr-x root root 39408 2008-02-29 01:16 runtime

-rwxr-xr-x root root 2920 2008-02-29 01:16 system_server

-rwxr-xr-x root root 9168 2008-02-29 01:17 pv

Where are the SQLite databases on an Android Device?

By default, the SQLite databases have an extension .db. For example, a NotePad application may use note_pad.db database. This might be created from code using Android SDK’s SQLite classes/methods. By default, the SQLite database for an application is in
the /data/data/<app>/databases directory. As you can see from the listing below, the notepad database is in the /data/data/com.google.android.notepad/databases directory.

Code Listing 2. The location of the notepad database

# pwd

pwd

/data/data/com.google.android.notepad/databases

# ls -l

ls -l

-rw-rw---- app_8 app_8 3072 2008-03-18 18:23 note_pad.db

You can see a whole bunch of these sub-directories under the /data/data directory.

Code Listing 3. The /data/data directory

# pwd

pwd

/data/data

# ls

ls

com.google.android.notepad

com.google.android.samples

com.google.android.gtalkservice

com.google.android.phone

com.google.android.maps

com.google.android.providers.im

com.google.android.home

com.google.android.googleapps

com.google.android.gtalksettings

com.google.android.fallback

com.google.android.development

com.google.android.contacts

com.google.android.browser

com.google.android.providers.telephony

com.google.android.providers.settings

com.google.android.providers.media

com.google.android.masfproxyservice

com.google.android.providers.googleapps

com.google.android.providers.contacts

android

Starting the SQLite command line program

Starting generically

Typing sqlite3 in the Android Shell will open the SQLite command line program (since sqlite3 is in the /system/bin directory). Typing .help gives the summarized set of commands available from here.

Code Listing 4. The SQLite commands available from the command line utility

# sqlite3

sqlite3

SQLite version 3.5.0

Enter ".help" for instructions

sqlite> .help

.help

.bail ON|OFF Stop after hitting an error. Default OFF

.databases List names and files of attached databases

.dump ?TABLE? ... Dump the database in an SQL text format

.echo ON|OFF Turn command echo on or off

.exit Exit this program

.explain ON|OFF Turn output mode suitable for EXPLAIN on or off.

.header(s) ON|OFF Turn display of headers on or off

.help Show this message

.import FILE TABLE Import data from FILE into TABLE

.indices TABLE Show names of all indices on TABLE

.load FILE ?ENTRY? Load an extension library

.mode MODE ?TABLE? Set output mode where MODE is one of:

csv Comma-separated values

column Left-aligned columns. (See .width)

html HTML <table> code

insert SQL insert statements for TABLE

line One value per line

list Values delimited by .separator string

tabs Tab-separated values

tcl TCL list elements

.nullvalue STRING Print STRING in place of NULL values

.output FILENAME Send output to FILENAME

.output stdout Send output to the screen

.prompt MAIN CONTINUE Replace the standard prompts

.quit Exit this program

.read FILENAME Execute SQL in FILENAME

.schema ?TABLE? Show the CREATE statements

.separator STRING Change separator used by output mode and .import

.show Show the current values for various settings

.tables ?PATTERN? List names of tables matching a LIKE pattern

.timeout MS Try opening locked tables for MS milliseconds

.width NUM NUM ... Set column widths for "column" mode

sqlite>

Opening a database

You would, of course, want to see the data and structure of a particular database. In the listing below, the note_pad.db is opened for further querying. Here, I went to the directory where the database is; however, you can also specify the full path.

Code Listing 5. Opening a specific database from SQLite command line

# pwd

pwd

/data/data/com.google.android.notepad/databases

# ls

ls

note_pad.db

# sqlite3 note_pad.db

sqlite3 note_pad.db

SQLite version 3.5.0

Enter ".help" for instructions

sqlite>

Example Commands from the SQLite command line program

Getting the list of tables

You can get the list of all the tables in the current database in two ways: from the .tables command or by querying the sqlite_master table.

Code Listing 6. List of tables

sqlite> .tables

.tables

android_metadata notes

sqlite> select * from sqlite_master;

select * from sqlite_master;

table|android_metadata|android_metadata|2|CREATE TABLE android_metadata (locale

TEXT)

table|notes|notes|3|CREATE TABLE notes (_id INTEGER PRIMARY KEY,title TEXT,note

TEXT,created INTEGER,modified INTEGER)

Getting the schema of the tables

By using the .schema command, you can get the schema of either all of the tables or a single table.

Code Listing 7. Schema of tables

sqlite> .schema

.schema

CREATE TABLE android_metadata (locale TEXT);

CREATE TABLE notes (_id INTEGER PRIMARY KEY,title TEXT,note TEXT,created INTEGER

,modified INTEGER);

sqlite> .schema notes

.schema notes

CREATE TABLE notes (_id INTEGER PRIMARY KEY,title TEXT,note TEXT,created INTEGER

,modified INTEGER);

SQL Queries

You can issue queries like ‘select * from notes’ to get the data from the notes table. As you can see from the figure below, I have entered a series of notes in the notepad application.

Figure 1. Notes in the Note pad application

After entering the notes, if you query the notes table, you will get the data in the _id, title, note, created, and modified columns.

Code Listing 8. Data from notes

sqlite> .schema notes

.schema notes

CREATE TABLE notes (_id INTEGER PRIMARY KEY,title TEXT,note TEXT,created INTEGER

,modified INTEGER);

sqlite> select * from notes;

select * from notes;

1|Title of Note

This is a test note.|This is a test note.|1205871448827|1205873944838

3|Another note

Some text.|A third note

Some text.|1205873990394|1205874145996

4|One more

Body here|One more

Body here|1205874074992|1205874088072

And, finally, we can take a look at how this table was created.

Code Listing 9. Creation of the notes table

public class NotePadProvider extends ContentProvider {

…

private static class DatabaseHelper extends SQLiteOpenHelper {

@Override

public void onCreate(SQLiteDatabase db) {

db.execSQL("CREATE TABLE notes (_id INTEGER PRIMARY KEY,"

+ "title TEXT," + "note TEXT," + "created INTEGER,"

+ "modified INTEGER" + ");");

}

…

}

…

@Override

public boolean onCreate() {

DatabaseHelper dbHelper = new DatabaseHelper();

mDB = dbHelper.openDatabase(getContext(), DATABASE_NAME, null, DATABASE_VERSION);

return (mDB == null) ? false : true;

}

…

}

As you can see above, CREATE TABLE sql has been used to create the notes table. Classes like SQLiteOpenHelper and ContentProvider from Android SDK are put to use here.

PS：原文地址http://www.infinitezest.com/articles/using-sqlite-from-shell-in-android.aspx