how do i dump a single sqlite3 table in python?

问题:

I would like to dump only one table but by the looks of it there is no parameter for this.

I found this example of the dump but is is for all tables:

# Convert file existing_db.db to SQL dump file dump.sql
import sqlite3, os

con = sqlite3.connect('existing_db.db')
with open('dump.sql', 'w') as f:
    for line in con.iterdump():
        f.write('%s\n' % line)

回答1:

You can copy only the single table in an in memory db:

import sqlite3

def getTableDump(db_file, table_to_dump):
    conn = sqlite3.connect(':memory:')    
    cu = conn.cursor()
    cu.execute("attach database '" + db_file + "' as attached_db")
    cu.execute("select sql from attached_db.sqlite_master "
               "where type='table' and name='" + table_to_dump + "'")
    sql_create_table = cu.fetchone()[0]
    cu.execute(sql_create_table);
    cu.execute("insert into " + table_to_dump +
               " select * from attached_db." + table_to_dump)
    conn.commit()
    cu.execute("detach database attached_db")
    return "\n".join(conn.iterdump())

TABLE_TO_DUMP = 'table_to_dump'
DB_FILE = 'db_file'

print getTableDump(DB_FILE, TABLE_TO_DUMP)

Pro: Simplicity and reliability: you don't have to re-write any library method, and you are more assured that the code is compatible with future versions of the sqlite3 module.

Con: You need to load the whole table in memory, which may or may not be a big deal depending on how big the table is, and how much memory is available.

回答2:

Dump realization lies here http://coverage.livinglogic.de/Lib/sqlite3/dump.py.html (local path: PythonPath/Lib/sqlite3/dump.py)

You can modify it a little:

# Mimic the sqlite3 console shell's .dump command
# Author: Paul Kippes <[e-mail]>

def _iterdump(connection, table_name):
    """
    Returns an iterator to the dump of the database in an SQL text format.

    Used to produce an SQL dump of the database.  Useful to save an in-memory
    database for later restoration.  This function should not be called
    directly but instead called from the Connection method, iterdump().
    """

    cu = connection.cursor()
    table_name = table_name

    yield('BEGIN TRANSACTION;')

    # sqlite_master table contains the SQL CREATE statements for the database.
    q = """
       SELECT name, type, sql
        FROM sqlite_master
            WHERE sql NOT NULL AND
            type == 'table' AND
            name == :table_name
        """
    schema_res = cu.execute(q, {'table_name': table_name})
    for table_name, type, sql in schema_res.fetchall():
        if table_name == 'sqlite_sequence':
            yield('DELETE FROM sqlite_sequence;')
        elif table_name == 'sqlite_stat1':
            yield('ANALYZE sqlite_master;')
        elif table_name.startswith('sqlite_'):
            continue
        else:
            yield('%s;' % sql)

        # Build the insert statement for each row of the current table
        res = cu.execute("PRAGMA table_info('%s')" % table_name)
        column_names = [str(table_info[1]) for table_info in res.fetchall()]
        q = "SELECT 'INSERT INTO \"%(tbl_name)s\" VALUES("
        q += ",".join(["'||quote(" + col + ")||'" for col in column_names])
        q += ")' FROM '%(tbl_name)s'"
        query_res = cu.execute(q % {'tbl_name': table_name})
        for row in query_res:
            yield("%s;" % row[0])

    # Now when the type is 'index', 'trigger', or 'view'
    #q = """
    #    SELECT name, type, sql
    #    FROM sqlite_master
    #        WHERE sql NOT NULL AND
    #        type IN ('index', 'trigger', 'view')
    #    """
    #schema_res = cu.execute(q)
    #for name, type, sql in schema_res.fetchall():
    #    yield('%s;' % sql)

    yield('COMMIT;')

Now it accepts table name as second argument.
You can use it like this:

with open('dump.sql', 'w') as f:
    for line in _iterdump(con, 'GTS_vehicle'):
        f.write('%s\n' % line)

Will get something like:

BEGIN TRANSACTION;
CREATE TABLE "GTS_vehicle" ("id" integer NOT NULL PRIMARY KEY, "name" varchar(20) NOT NULL, "company_id" integer NULL, "license_plate" varchar(20) NULL, "icon" varchar(100) NOT NULL DEFAULT 'baseicon.png', "car_brand" varchar(30) NULL, "content_type_id" integer NULL, "modemID" varchar(100) NULL, "distance" integer NULL, "max_speed" integer NULL DEFAULT 100, "max_rpm" integer NULL DEFAULT 4000, "fuel_tank_volume" integer NULL DEFAULT 70, "max_battery_voltage" integer NULL, "creation_date" datetime NOT NULL, "last_RFID" text NULL);
INSERT INTO "GTS_vehicle" VALUES(1,'lan1_op1_car1',1,'03115','baseicon.png','UFP',16,'lan_op1_car1',NULL,100,4000,70,12,'2011-06-23 11:54:32.395000',NULL);
INSERT INTO "GTS_vehicle" VALUES(2,'lang_op1_car2',1,'03','baseicon.png','ыва',16,'lan_op1_car2',NULL,100,4000,70,12,'2011-06-23 11:55:02.372000',NULL);
INSERT INTO "GTS_vehicle" VALUES(3,'lang_sup_car1',1,'0000','baseicon.png','Fiat',16,'lan_sup_car1',NULL,100,4000,70,12,'2011-06-23 12:32:09.017000',NULL);
INSERT INTO "GTS_vehicle" VALUES(4,'lang_sup_car2',1,'123','baseicon.png','ЗАЗ',16,'lan_sup_car2',NULL,100,4000,70,12,'2011-06-23 12:31:38.108000',NULL);
INSERT INTO "GTS_vehicle" VALUES(9,'lang_op2_car1',1,'','baseicon.png','',16,'1233211234',NULL,100,4000,70,12,'2011-07-05 13:32:09.865000',NULL);
INSERT INTO "GTS_vehicle" VALUES(11,'Big RIder',1,'','baseicon.png','0311523',16,'111',NULL,100,4000,70,20,'2011-07-07 12:12:40.358000',NULL);
COMMIT;

回答3:

By iterdump(), all information would be displayed like this:

INSERT INTO "name" VALUES(1, 'John')
INSERT INTO "name" VALUES(2, 'Jane')
INSERT INTO "phone" VALUES(1, '111000')
INSERT INTO "phone" VALUES(2, '111001')

An easy way is by filter certain keywords by string.startswith() method. For example, the table name is 'phone':

# Convert file existing_db.db to SQL dump file dump.sql
import sqlite3, os

con = sqlite3.connect('existing_db.db')
with open('dump.sql', 'w') as f:
    for line in con.iterdump():
        if line.startswith('INSERT INTO "phone"'):
            f.write('%s\n' % line)

Not very smart, but can fit your objective.