'sqlite' Tutorial for POPFile 0.21.0 to 1.0.1

'sqlite' is a command-line program to administer SQLite 2.x databases as used by POPFile 0.21.0 to 1.0.1. This utility is called sqlite.exe or sqlite depending upon the platform. For simplicity this tutorial refers to the utility as sqlite.

POPFile 1.1.0 (or later) uses the SQLite 3.x format for its database which requires a different command-line program (sqlite3.exe or sqlite3). There is a tutorial showing how to use this SQLite 3.x format utility on the SQLite website.

Introduction

POPFile uses an SQLite database to hold essential information, such as the corpus used to classify the messages it handles. POPFile versions 0.21.0 to 1.0.1 only work with SQLite 2.x libraries (none of these versions can work with SQLite 3.x libraries).

The SQLite library includes a simple command-line utility that allows the user to manually enter and execute SQL commands against an SQLite database. Databases built using SQLite 2.x libraries are not compatible with databases built using the SQLite 3.x libraries. Therefore there are separate command-line utilities: sqlite for SQLite 2.x format databases and sqlite3 for SQLite 3.x format databases.

The SQLite web site only seems to document the sqlite3 utility which is not compatible with the SQLite databases created by POPFile 0.21.0 to 1.0.1 (POPFile 1.1.0, or later, uses SQLite 3.x). The information on this wiki page is based upon an old page (last modified on 2004/05/31 15:06:30) from the SQLite web site which documented the features supported by the sqlite command-line utility.

The SQLite web site's download page no longer has links for the old sqlite command-line utility (Windows and Linux binary versions used to be listed under “Historical Binaries And Source Code”) but the SQLite 2.8 source code is still available. (POPFile's Windows installer includes a SQLite 2.x version of the sqlite.exe command-line utility.)

Getting Started

To start the sqlite program, just type sqlite at the command prompt 1) followed by the name of the file that holds the SQLite database. If the file does not exist, a new one is created automatically (NOTE: The program will not warn that it has created an empty SQLite database). The sqlite 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:

$ sqlite ex1
SQLite version 2.8.17
Enter ".help" for instructions
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 sqlite program by typing your system's End-Of-File character (usually a Control-D) or the interrupt character (usually a Control-C).

Make sure you type a semicolon at the end of each SQL command! The sqlite program looks for a semicolon to know when your SQL command is complete. If you omit the semicolon, sqlite 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:

$ sqlite ex1
SQLite version 2.8.17
Enter ".help" for instructions
sqlite> .mode lines
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 'sqlite'

Most of the time, sqlite 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 sqlite 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
.databases             List names and files of attached databases
.dump ?TABLE? ...      Dump the database in a 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
.indices TABLE         Show names of all indices on TABLE
.mode MODE             Set mode to one of "line(s)", "column(s)",
                       "insert", "list", or "html"
.mode insert TABLE     Generate SQL insert statements for TABLE
.nullvalue STRING      Print STRING instead of nothing for NULL data
.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 string for "list" mode
.show                  Show the current values for various settings
.tables ?PATTERN?      List names of tables matching a pattern
.timeout MS            Try opening locked tables for MS milliseconds
.width NUM NUM ...     Set column widths for "column" mode
sqlite>

Changing Output Formats

The sqlite program is able to show the results of a query in five different formats: “line”, “column”, “list”, “html”, and “insert”. 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> .headers on
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> .headers on
sqlite> .mode column
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, sqlite writes the results of the query as an XHTML table. The beginning <TABLE> and the ending </TABLE> are not written, but all of the intervening <TR>s, <TH>s, and <TD>s are. For example:

sqlite> .mode html
sqlite> select * from tbl1;
<TR><TD>hello!</TD>
<TD>10</TD>
</TR>
<TR><TD>goodbye</TD>
<TD>20</TD>
</TR>
sqlite>

The html output mode is envisioned as being useful for CGI.

Writing results to a file

By default, sqlite 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 sqlite 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 equvalent to executing the following query:

SELECT name FROM sqlite_master WHERE type='table'
UNION ALL SELECT name FROM sqlite_temp_master WHERE type='table'
ORDER BY name;

In fact, if you look at the source code to the sqlite 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 tbl_name LIKE '%s' AND type!='meta'
ORDER BY type DESC, name;

The %s in the query above is replaced by the argument to .schema, of course. Notice that the argument to the .schema command appears to the right of an SQL LIKE operator. So you can use wildcards in the name of the table. For example, to get the schema for all tables whose names contain the character string “abc” you could enter:

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.

C:\TEMP> sqlite ex1.db
SQLite version 2.8.17
Enter ".help" for instructions
sqlite> .databases
seq  name             file

---  ---------------  ---------------------------------

0    main             C:\TEMP\ex1.db

1    temp             C:\TEMP\sqlite_wk2nfpGbeTwPGOz

sqlite>

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 sqlite.

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

$ echo '.dump' | sqlite 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 | sqlite ex2

The text format used is the same as used by PostgreSQL, so you can also use the .dump command to export an SQLite database into a PostgreSQL database. Like this:

$ createdb ex2
$ echo '.dump' | sqlite ex1 | psql ex2

You can almost (but not quite) go the other way and export a PostgreSQL database into SQLite using the pg_dump utility. Unfortunately, when pg_dump writes the database schema information, it uses some SQL syntax that SQLite does not understand. So you cannot pipe the output of pg_dump directly into sqlite. But if you can recreate the schema separately, you can use pg_dump with the -a option to list just the data of a PostgreSQL database and import that directly into SQLite.

$ sqlite ex3 <schema.sq1
$ pg_dump -a ex2 | sqlite ex3

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     Transaction   0           0
1     VerifyCookie  0           180
2     Transaction   1           0
3     Integer       0           0
4     OpenRead      0           3           tbl1
5     Rewind        0           12
6     Column        0           1
7     Integer       20          0           20
8     Ge            1           11
9     Recno         0           0
10    ListWrite     0           0
11    Next          0           6
12    Close         0           0
13    ListRewind    0           0
14    Integer       0           0
15    OpenWrite     0           3           tbl1
16    ListRead      0           20
17    NotExists     0           19
18    Delete        0           5
19    Goto          0           16
20    ListReset     0           0
21    Close         0           0
22    SetCounts     0           0
23    Commit        0           0
24    Halt          0           0
sqlite>

The .timeout command sets the amount of time that the sqlite 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 sqlite program to exit (.quit and .q can also be used to exit).

Using sqlite in a shell script

One way to use sqlite in a shell script is to use echo or cat to generate a sequence of commands in a file, then invoke sqlite while redirecting input from the generated command file. This works fine and is appropriate in many circumstances. But as an added convenience, sqlite allows a single SQL command to be entered on the command line as a second argument after the database name. When the sqlite 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 sqlite easy to use in conjunction with programs like awk. For example:

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

Ending shell commands

SQLite commands are normally terminated by a semicolon. In the shell you can also use the word “GO” (case-insensitive) or a backslash character “\” on a line by itself to end a command. These are used by SQL Server and Oracle, respectively. These won't work in sqlite_exec(), because the shell translates these into a semicolon before passing them to that function.

Compiling the sqlite program from sources

The sqlite program is built automatically when you compile the SQLite library. Just get a copy of the source tree, run configure and then make.

1) If you want to use sqlite with an existing SQLite database file it is best to change to the directory containing the database file before you run sqlite
 
howtos/sqlite_tutorial.txt · Last modified: 2013/10/25 14:52 by xuesheng

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