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<title>GNOME Data Access 5 manual: Meta data</title>
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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id-1.8.6.6"></a>Meta data</h2></div></div></div>
<p>
When a connection is opened for the first time, the tool get all the possible meta data associated to that connection (list of
tables, table's columns and their constraints, views, etc). The meta data are referred to when the user wants for example
to list a table's attributes, or for command line completion.
</p>
<p>
If some modifications to the database structure have been made using a tool not using <span class="application">Libgda</span>, then
the meta data must be updated using the <span class="command"><strong>.meta</strong></span> command, which does not output
anything unless an error occurred. Updates to the meta data are automatic when a shema change
is done using <span class="application">Libgda</span> if the connection has been opened using the GDA_CONNECTION_OPTIONS_AUTO_META_DATA flag
(which is the case for <span class="application">Libgda</span>'s own tools).
</p>
<p>
As the meta data are also stored in a database, the console tool allows one to directly execute SQL commands in the
meta data database associated to a connection. The meta data connection associated to a connection is by convention named
as the tilde character concatenated with the connection name (for example if the connection is named "cnc1", then the connection
to its meta data will be named "~cnc1"). To open a meta data connection, make sure the current connection is the one for which
you want to access the meta data, and then use the <span class="command"><strong>.c ~</strong></span> command (note that the same command will
return to the "cnc1" connection):
</p>
<pre class="programlisting">
cnc1> .c ~
Getting database schema information, this may take some time... Done.
~cnc1> .dt
List of tables
Schema | Name | Type | Owner | Description
-------+----------------------------------+------------+-------+------------
main | _attributes | BASE TABLE | |
main | _builtin_data_types | BASE TABLE | |
main | _character_sets | BASE TABLE | |
main | _check_column_usage | BASE TABLE | |
main | _collations | BASE TABLE | |
main | _columns | BASE TABLE | |
main | _domain_constraints | BASE TABLE | |
main | _domains | BASE TABLE | |
main | _element_types | BASE TABLE | |
main | _enums | BASE TABLE | |
main | _information_schema_catalog_name | BASE TABLE | |
main | _key_column_usage | BASE TABLE | |
main | _parameters | BASE TABLE | |
main | _referential_constraints | BASE TABLE | |
main | _routine_columns | BASE TABLE | |
main | _routines | BASE TABLE | |
main | _schemata | BASE TABLE | |
main | _table_constraints | BASE TABLE | |
main | _tables | BASE TABLE | |
main | _triggers | BASE TABLE | |
main | _udt | BASE TABLE | |
main | _udt_columns | BASE TABLE | |
main | _view_column_usage | BASE TABLE | |
main | _views | BASE TABLE | |
main | gda_sql_query_buffers | BASE TABLE | |
(25 rows)
~cnc1> SELECT table_name FROM _tables;
table_name
---------------
customers
locations
orders
order_contents
roles
salesrep
sales_orga
warehouses
categories
products
products_copied
(11 rows)
~cnc1> .c ~
cnc1>
</pre>
<p>
Also note that the meta data's connections are listed among the opened connections, as shown:
</p>
<pre class="programlisting">
cnc1> .c
List of opened connections
Name | Provider | DSN or connection string | Username
------+----------+-------------------------------------------------------+---------
cnc1 | SQLite | SalesTest |
~cnc1 | SQLite | DB_DIR=/home/vivien/.libgda;DB_NAME=gda-sql-SalesTest |
(2 rows)
cnc1>
</pre>
<p>
</p>
<p>
It is possible for any application to create some extra objects in that database for its own purposes, with the
constraint that it <span class="emphasis"><em>should not</em></span> create objects with names starting with an underscore (these
names are reserved for <span class="application">Libgda</span>'s own purposes). In the previous example, the table named "gda_sql_query_buffers"
is the table internally used by the console tool to store the contents of named query buffers.
</p>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.8.6.6.6"></a>Information about tables</h3></div></div></div>
<p>
Use the <span class="command"><strong>.dt</strong></span> command to list all the tables (or list only one table if the table name is specified as
an argument to the command):
</p>
<pre class="programlisting">
cnc1> .dt
List of tables
Schema | Name | Type | Owner | Description
-------+-----------------+------------+-------+------------
main | categories | BASE TABLE | |
main | customers | BASE TABLE | |
main | locations | BASE TABLE | |
main | order_contents | BASE TABLE | |
main | orders | BASE TABLE | |
main | products | BASE TABLE | |
main | products_copied | BASE TABLE | |
main | roles | BASE TABLE | |
main | sales_orga | BASE TABLE | |
main | salesrep | BASE TABLE | |
main | warehouses | BASE TABLE | |
(11 rows)
cnc1> .dt customers
List of tables
Schema | Name | Type | Owner | Description
-------+-----------+------------+-------+------------
main | customers | BASE TABLE | |
(1 row)
cnc1>
</pre>
<p>
</p>
<p>
To display the details about a single table, use the <span class="command"><strong>.d <table_name></strong></span> command:
</p>
<pre class="programlisting">
cnc1> .d customers
List of columns for table 'customers'
Column | Type | Nullable | Default | Extra
------------------+---------+----------+---------+---------------
id | integer | no | | Auto increment
name | string | no | '' |
default_served_by | integer | yes | |
country | string | yes | |
city | string | yes | |
(5 rows)
Primary key 'primary_key' (id)
Foreign key 'fk_locations' (country, city) references main.locations (country, city)
Foreign key 'fk_salesrep' (default_served_by) references main.salesrep (default_served_by)
cnc1>
</pre>
<p>
</p>
<p>
Finally, the <span class="command"><strong>.graph [TABLE1 [TABLE2...]]</strong></span> will create a graph of all the tables (or
only the tables mentioned as arguments). The graph creates a <span class="application">GraphViz</span> file
named "graph.dot" which can then be processed with the GraphViz'<span class="command"><strong>dot</strong></span> command to
produce an image or a PDF file for example.
</p>
<p>
If the <code class="envar">GDA_SQL_VIEWER_PNG</code> or <code class="envar">GDA_SQL_VIEWER_PDF</code> environment variables are set
(for example to <span class="application">eog</span> or <span class="application">evince</span>) and if the <span class="command"><strong>dot</strong></span> command
is installed, then the console tool will perform the transformation and display the graph (if under a graphical session).
The following figure shows an example of graph:
</p>
<div class="mediaobject"><img src="gda-sql-graph.png" width="496" alt='Sample output from the ".graph" command'></div>
<p>
</p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.8.6.6.7"></a>Information about views</h3></div></div></div>
<p>
The console tool can report information about views. Use the <span class="command"><strong>.dv</strong></span> command to list all the views
(or list only one view if the view name is specified as an argument to the command):
</p>
<pre class="programlisting">
cnc1> .dv
List of views
Schema | Name | Type | Owner | Description
-------+--------------+------+-------+------------
main | cust_summary | VIEW | |
(1 row)
cnc1>
</pre>
<p>
</p>
<p>
One can also get more information for a single view using the <span class="command"><strong>.d <view name></strong></span> command,
for example:
</p>
<pre class="programlisting">
cnc1> .d cust_summary
List of columns for view 'cust_summary'
Column | Type | Nullable | Default | Extra
---------+--------+----------+---------+------
name | string | yes | |
shortcut | string | yes | |
(2 rows)
View definition: CREATE VIEW cust_summary as SELECT c.name, l.shortcut FROM customers c LEFT JOIN locations l ON (c.country=l.country AND c.city=l.city)
cnc1>
</pre>
<p>
</p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.8.6.6.8"></a>Information about schemas</h3></div></div></div>
<p>
Some databases feature the notion of <span class="emphasis"><em>schema</em></span> which is a container for database objects such as
tables, views, etc. Use the <span class="command"><strong>.dn</strong></span> command to get a list of all the schemas in a database. For
example with a PostgreSQL database:
</p>
<pre class="programlisting">
List of schemas
Schema | Owner | Internal
-------------------+----------+---------
information_schema | postgres | yes
pg_catalog | postgres | yes
pg_temp_1 | postgres | yes
pg_toast | postgres | yes
pg_toast_temp_1 | postgres | yes
public | postgres | no
(6 rows)
cnc1>
</pre>
<p>
</p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.8.6.6.9"></a>Information about other objects</h3></div></div></div>
<p>
The meta data database holds a lot of information about the many objects which exist in a database, but the
console tool does not provide internal commands to display all of them. The solution is to run SELECT commands
in the meta data connection associated to a connection. For example to get a list of triggers where the "cnc2"
is a connection opened to a PostgreSQL's database, one first needs to connection to the meta data connection
and lookup into the "_triggers" table:
</p>
<pre class="programlisting">
cnc2> .c ~
~cnc2> select trigger_name, event_manipulation, event_object_table from _triggers;
trigger_name | event_manipulation | event_object_table
------------------------+--------------------+-------------------
pg_sync_pg_database | INSERT | pg_database
pg_sync_pg_database | DELETE | pg_database
pg_sync_pg_database | UPDATE | pg_database
pg_sync_pg_authid | INSERT | pg_authid
pg_sync_pg_authid | DELETE | pg_authid
pg_sync_pg_authid | UPDATE | pg_authid
pg_sync_pg_auth_members | INSERT | pg_auth_members
pg_sync_pg_auth_members | DELETE | pg_auth_members
pg_sync_pg_auth_members | UPDATE | pg_auth_members
(9 rows)
~cnc2>
</pre>
<p>
</p>
<p>
The meta data's database structure is described in the <a class="link" href="information_schema.html" title="Database structure">related section</a>.
</p>
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