sqlite.tcl

sqlite-3.4.1,嵌入式数据库.是一个功能强大的开源数据库,给学习和研发以及小型公司的发展带来了全所未有的好处.

sqlite> (((select * from tbl1;)))
INSERT INTO 'new_table' VALUES('hello',10);
INSERT INTO 'new_table' VALUES('goodbye',20);
sqlite>
}

puts {
<p>The last output mode is "html".  In this mode, sqlite3 writes
the results of the query as an XHTML table.  The beginning
&lt;TABLE&gt; and the ending &lt;/TABLE&gt; are not written, but
all of the intervening &lt;TR&gt;s, &lt;TH&gt;s, and &lt;TD&gt;s
are.  The html output mode is envisioned as being useful for
CGI.</p>
}

puts {
<h3>Writing results to a file</h3>

<p>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:</p>}

Code {
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
$
}

puts {
<h3>Querying the database schema</h3>

<p>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.</p>

<p>For example, to see a list of the tables in the database, you
can enter ".tables".</p>
}

Code {
sqlite> (((.tables)))
tbl1
tbl2
sqlite>
}

puts {
<p>The ".tables" command is similar to setting list mode then
executing the following query:</p>

<blockquote><pre>
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
</pre></blockquote>

<p>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.</p>

<p>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:</p>}

Code {
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>
}

puts {
<p>The ".schema" command accomplishes the same thing as setting
list mode, then entering the following query:</p>

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

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

<blockquote><pre>
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
</pre></blockquote>

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

<blockquote><pre>
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
</pre></blockquote>

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

Code {
sqlite> (((.schema %abc%)))
}

puts {
<p>
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.</p>

<p>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.</p>}

Code {
sqlite> (((.databases)))
}

puts {
<h3>Converting An Entire Database To An ASCII Text File</h3>

<p>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 <b>sqlite3</b>.</p>

<p>A good way to make an archival copy of a database is this:</p>
}

Code {
$ (((echo '.dump' | sqlite3 ex1 | gzip -c >ex1.dump.gz)))
}

puts {
<p>This generates a file named <b>ex1.dump.gz</b> that contains everything
you need to reconstruct the database at a later time, or on another
machine.  To reconstruct the database, just type:</p>
}

Code {
$ (((zcat ex1.dump.gz | sqlite3 ex2)))
}

puts {
<p>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:</p>
}

Code {
$ (((createdb ex2)))
$ (((sqlite3 ex1 .dump | psql ex2)))
}

puts {
<h3>Other Dot Commands</h3>

<p>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:</p>}

Code {
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                  
}

puts {

<p>The ".timeout" command sets the amount of time that the <b>sqlite3</b>
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.</p>

<p>And finally, we mention the ".exit" command which causes the
sqlite3 program to exit.</p>

<h3>Using sqlite3 in a shell script</h3>

<p>
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:</p>}

Code {
$ (((sqlite3 ex1 'select * from tbl1' |)))
> ((( awk '{printf "<tr><td>%s<td>%s\n",$1,$2 }')))
<tr><td>hello<td>10
<tr><td>goodbye<td>20
$
}

puts {
<h3>Ending shell commands</h3>

<p>
SQLite commands are normally terminated by a semicolon.  In the shell 
you can also use the word "GO" (case-insensitive) or a slash character 
"/" on a line by itself to end a command.  These are used by SQL Server 
and Oracle, respectively.  These won't work in <b>sqlite3_exec()</b>, 
because the shell translates these into a semicolon before passing them 
to that function.</p>
}

puts {
<h3>Compiling the sqlite3 program from sources</h3>

<p>
The sqlite3 program is built automatically when you compile the
SQLite library.  Just get a copy of the source tree, run
"configure" and then "make".</p>
}
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