remove sqlite puzzle

sqlite database puzzled me for a long time, when I got start to C. so far I get the core operation of this DB.
here is the mannal from SQlite.

To start the sqlite3 program, just type "sqlite3" followed by the name the file that holds the SQLite database. If the file does not exist, a new one is created automatically. The sqlite3 program will then prompt you to enter SQL. Type in SQL statements (terminated by a semicolon), press "Enter" and the SQL will be executed.

For example, to create a new SQLite database named "ex1" with a single table named "tbl1", you might do this:

$ sqlite3 ex1
SQLite version 3.6.11
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> create table tbl1(one varchar(10), two smallint);
sqlite> insert into tbl1 values('hello!',10);
sqlite> insert into tbl1 values('goodbye', 20);
sqlite> select * from tbl1;
hello!|10
goodbye|20
sqlite>

You can terminate the sqlite3 program by typing your systems End-Of-File character (usually a Control-D). Use the interrupt character (usually a Control-C) to stop a long-running SQL statement.

Make sure you type a semicolon at the end of each SQL command! The sqlite3 program looks for a semicolon to know when your SQL command is complete. If you omit the semicolon, sqlite3 will give you a continuation prompt and wait for you to enter more text to be added to the current SQL command. This feature allows you to enter SQL commands that span multiple lines. For example:

sqlite> CREATE TABLE tbl2 (
   ...>   f1 varchar(30) primary key,
   ...>   f2 text,
   ...>   f3 real
   ...> );
sqlite>

Aside: Querying the SQLITE_MASTER table

The database schema in an SQLite database is stored in a special table named "sqlite_master". You can execute "SELECT" statements against the special sqlite_master table just like any other table in an SQLite database. For example:

$ sqlite3 ex1
SQLite vresion 3.6.11
Enter ".help" for instructions
sqlite> select * from sqlite_master;
    type = table
    name = tbl1
tbl_name = tbl1
rootpage = 3
     sql = create table tbl1(one varchar(10), two smallint)
sqlite>

But you cannot execute DROP TABLE, UPDATE, INSERT or DELETE against the sqlite_master table. The sqlite_master table is updated automatically as you create or drop tables and indices from the database. You can not make manual changes to the sqlite_master table.

The schema for TEMPORARY tables is not stored in the "sqlite_master" table since TEMPORARY tables are not visible to applications other than the application that created the table. The schema for TEMPORARY tables is stored in another special table named "sqlite_temp_master". The "sqlite_temp_master" table is temporary itself.

Special commands to sqlite3

Most of the time, sqlite3 just reads lines of input and passes them on to the SQLite library for execution. But if an input line begins with a dot ("."), then that line is intercepted and interpreted by the sqlite3 program itself. These "dot commands" are typically used to change the output format of queries, or to execute certain prepackaged query statements.

For a listing of the available dot commands, you can enter ".help" at any time. For example:

sqlite> .help
.backup ?DB? FILE      Backup DB (default "main") to FILE
.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.
.genfkey ?OPTIONS?     Options are:
                         --no-drop: Do not drop old fkey triggers.
                         --ignore-errors: Ignore tables with fkey errors
                         --exec: Execute generated SQL immediately
                       See file tool/genfkey.README in the source 
                       distribution for further information.
.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
.iotrace FILE          Enable I/O diagnostic logging to FILE
.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  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
.restore ?DB? FILE     Restore content of DB (default "main") from FILE
.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
.timer ON|OFF          Turn the CPU timer measurement on or off
.width NUM NUM ...     Set column widths for "column" mode
sqlite>
Changing Output Formats
The sqlite3 program is able to show the results of a query
in eight different formats: "csv", "column", "html", "insert",
"line", "list", "tabs", and "tcl".
You can use the ".mode" dot command to switch between these output
formats.
The default output mode is "list".  In
list mode, each record of a query result is written on one line of
output and each column within that record is separated by a specific
separator string.  The default separator is a pipe symbol ("|").
List mode is especially useful when you are going to send the output
of a query to another program (such as AWK) for additional processing.
sqlite> .mode list
sqlite> select * from tbl1;
hello|10
goodbye|20
sqlite>
You can use the ".separator" dot command to change the separator
for list mode.  For example, to change the separator to a comma and
a space, you could do this:
sqlite> .separator ", "
sqlite> select * from tbl1;
hello, 10
goodbye, 20
sqlite>
In "line" mode, each column in a row of the database
is shown on a line by itself.  Each line consists of the column
name, an equal sign and the column data.  Successive records are
separated by a blank line.  Here is an example of line mode
output:
sqlite> .mode line
sqlite> select * from tbl1;
one = hello
two = 10

one = goodbye
two = 20
sqlite>
In column mode, each record is shown on a separate line with the
data aligned in columns.  For example:
sqlite> .mode column
sqlite> select * from tbl1;
one         two       
----------  ----------
hello       10        
goodbye     20        
sqlite>
By default, each column is at least 10 characters wide. 
Data that is too wide to fit in a column is truncated.  You can
adjust the column widths using the ".width" command.  Like this:
sqlite> .width 12 6
sqlite> select * from tbl1;
one           two   
------------  ------
hello         10    
goodbye       20    
sqlite>
The ".width" command in the example above sets the width of the first
column to 12 and the width of the second column to 6.  All other column
widths were unaltered.  You can gives as many arguments to ".width" as
necessary to specify the widths of as many columns as are in your
query results.
If you specify a column a width of 0, then the column
width is automatically adjusted to be the maximum of three
numbers: 10, the width of the header, and the width of the
first row of data.  This makes the column width self-adjusting.
The default width setting for every column is this 
auto-adjusting 0 value.
The column labels that appear on the first two lines of output
can be turned on and off using the ".header" dot command.  In the
examples above, the column labels are on.  To turn them off you
could do this:
sqlite> .header off
sqlite> select * from tbl1;
hello         10    
goodbye       20    
sqlite>
Another useful output mode is "insert".  In insert mode, the output
is formatted to look like SQL INSERT statements.  You can use insert
mode to generate text that can later be used to input data into a 
different database.
When specifying insert mode, you have to give an extra argument
which is the name of the table to be inserted into.  For example:
sqlite> .mode insert new_table
sqlite> select * from tbl1;
INSERT INTO 'new_table' VALUES('hello',10);
INSERT INTO 'new_table' VALUES('goodbye',20);
sqlite>
The last output mode is "html".  In this mode, sqlite3 writes
the results of the query as an XHTML table.  The beginning
 and the ending  are not written, but
all of the intervening s, s, and s
are.  The html output mode is envisioned as being useful for
CGI.




Writing results to a file

By default, sqlite3 sends query results to standard output.  You
can change this using the ".output" command.  Just put the name of
an output file as an argument to the .output command and all subsequent
query results will be written to that file.  Use ".output stdout" to
begin writing to standard output again.  For example:

sqlite> .mode list
sqlite> .separator |
sqlite> .output test_file_1.txt
sqlite> select * from tbl1;
sqlite> .exit
$ cat test_file_1.txt
hello|10
goodbye|20
$


Querying the database schema

The sqlite3 program provides several convenience commands that
are useful for looking at the schema of the database.  There is
nothing that these commands do that cannot be done by some other
means.  These commands are provided purely as a shortcut.

For example, to see a list of the tables in the database, you
can enter ".tables".


sqlite> .tables
tbl1
tbl2
sqlite>


The ".tables" command is similar to setting list mode then
executing the following query:

SELECT name FROM sqlite_master 
WHERE type IN ('table','view') AND name NOT LIKE 'sqlite_%'
UNION ALL 
SELECT name FROM sqlite_temp_master 
WHERE type IN ('table','view') 
ORDER BY 1


In fact, if you look at the source code to the sqlite3 program
(found in the source tree in the file src/shell.c) you'll find
exactly the above query.

The ".indices" command works in a similar way to list all of
the indices for a particular table.  The ".indices" command takes
a single argument which is the name of the table for which the
indices are desired.  Last, but not least, is the ".schema" command.
With no arguments, the ".schema" command shows the original CREATE TABLE
and CREATE INDEX statements that were used to build the current database.
If you give the name of a table to ".schema", it shows the original
CREATE statement used to make that table and all if its indices.
We have:

sqlite> .schema
create table tbl1(one varchar(10), two smallint)
CREATE TABLE tbl2 (
  f1 varchar(30) primary key,
  f2 text,
  f3 real
)
sqlite> .schema tbl2
CREATE TABLE tbl2 (
  f1 varchar(30) primary key,
  f2 text,
  f3 real
)
sqlite>


The ".schema" command accomplishes the same thing as setting
list mode, then entering the following query:

SELECT sql FROM 
   (SELECT * FROM sqlite_master UNION ALL
    SELECT * FROM sqlite_temp_master)
WHERE type!='meta'
ORDER BY tbl_name, type DESC, name


Or, if you give an argument to ".schema" because you only
want the schema for a single table, the query looks like this:

SELECT sql FROM
   (SELECT * FROM sqlite_master UNION ALL
    SELECT * FROM sqlite_temp_master)
WHERE type!='meta' AND sql NOT NULL AND name NOT LIKE 'sqlite_%'
ORDER BY substr(type,2,1), name



You can supply an argument to the .schema command.  If you do, the
query looks like this:


SELECT sql FROM
   (SELECT * FROM sqlite_master UNION ALL
    SELECT * FROM sqlite_temp_master)
WHERE tbl_name LIKE '%s'
  AND type!='meta' AND sql NOT NULL AND name NOT LIKE 'sqlite_%'
ORDER BY substr(type,2,1), name


The "%s" in the query is replace by your argument.  This allows you
to view the schema for some subset of the database.


sqlite> .schema %abc%



Along these same lines,
the ".table" command also accepts a pattern as its first argument.
If you give an argument to the .table command, a "%" is both
appended and prepended and a LIKE clause is added to the query.
This allows you to list only those tables that match a particular
pattern.

The ".databases" command shows a list of all databases open in
the current connection.  There will always be at least 2.  The first
one is "main", the original database opened.  The second is "temp",
the database used for temporary tables. There may be additional 
databases listed for databases attached using the ATTACH statement.
The first output column is the name the database is attached with, 
and the second column is the filename of the external file.

sqlite> .databases


Converting An Entire Database To An ASCII Text File

Use the ".dump" command to convert the entire contents of a
database into a single ASCII text file.  This file can be converted
back into a database by piping it back into sqlite3.

A good way to make an archival copy of a database is this:


$ echo '.dump' | sqlite3 ex1 | gzip -c >ex1.dump.gz


This generates a file named ex1.dump.gz that contains everything
you need to reconstruct the database at a later time, or on another
machine.  To reconstruct the database, just type:


$ zcat ex1.dump.gz | sqlite3 ex2


The text format is pure SQL so you
can also use the .dump command to export an SQLite database
into other popular SQL database engines.  Like this:


$ createdb ex2
$ sqlite3 ex1 .dump | psql ex2


Other Dot Commands

The ".explain" dot command can be used to set the output mode
to "column" and to set the column widths to values that are reasonable
for looking at the output of an EXPLAIN command.  The EXPLAIN command
is an SQLite-specific SQL extension that is useful for debugging.  If any
regular SQL is prefaced by EXPLAIN, then the SQL command is parsed and
analyzed but is not executed.  Instead, the sequence of virtual machine
instructions that would have been used to execute the SQL command are
returned like a query result.  For example:

sqlite> .explain
sqlite> explain delete from tbl1 where two<20;
addr  opcode        p1     p2     p3          
----  ------------  -----  -----  -------------------------------------   
0     ListOpen      0      0                  
1     Open          0      1      tbl1        
2     Next          0      9                  
3     Field         0      1                  
4     Integer       20     0                  
5     Ge            0      2                  
6     Key           0      0                  
7     ListWrite     0      0                  
8     Goto          0      2                  
9     Noop          0      0                  
10    ListRewind    0      0                  
11    ListRead      0      14                 
12    Delete        0      0                  
13    Goto          0      11                 
14    ListClose     0      0



The ".timeout" command sets the amount of time that the sqlite3
program will wait for locks to clear on files it is trying to access
before returning an error.  The default value of the timeout is zero so
that an error is returned immediately if any needed database table or
index is locked.

And finally, we mention the ".exit" command which causes the
sqlite3 program to exit.

Using sqlite3 in a shell script


One way to use sqlite3 in a shell script is to use "echo" or
"cat" to generate a sequence of commands in a file, then invoke sqlite3
while redirecting input from the generated command file.  This
works fine and is appropriate in many circumstances.  But as
an added convenience, sqlite3 allows a single SQL command to be
entered on the command line as a second argument after the
database name.  When the sqlite3 program is launched with two
arguments, the second argument is passed to the SQLite library
for processing, the query results are printed on standard output
in list mode, and the program exits.  This mechanism is designed
to make sqlite3 easy to use in conjunction with programs like
"awk".  For example:

$ sqlite3 ex1 'select * from tbl1' |
>  awk '{printf "%s%s\n",$1,$2 }'
hello10
goodbye20
$