sqlite: A program to administer SQLite databases
(This page was last modified on 2002/06/27 13:21:02 UTC)
The SQLite library includes a simple command-line utility named sqlite that allows the user to manually enter and execute SQL commands against an SQLite database. This document provides a brief introduction on how to use sqlite.
Getting Started
To start the sqlite program, just type "sqlite" followed by the name the file that holds the SQLite database. If the file does not exist, a new one is created automatically. 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 2.0.0
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>
(In the example above, and in all subsequent examples, the commands you type are underlined and shown with a green tint and the responses from the computer are shown in black without underlining.)
You can terminate the sqlite program by typing your systems 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 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 vresion 2.0.0
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 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 .dump Dump database in a text format .exit Exit this program .explain Set output mode suitable for EXPLAIN .header 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", "column", "list", or "html" .mode insert TABLE Generate SQL insert statements for TABLE .output FILENAME Send output to FILENAME .output stdout Send output to the screen .schema ?TABLE? Show the CREATE statements .separator STRING Change separator string for "list" mode .tables List names all tables in the database .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> .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, 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. 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 the same as setting list mode then 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.
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.sql $ 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 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 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.
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
$
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".
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