Details about the HA DB (#1202)

* Add database documentation

* Add titles

source/_topics/database.markdown

@@ -0,0 +1,125 @@
+---
+layout: page
+title: "Home Assistant Database"
+description: "Details about the database which Home Assistant is using."
+date: 2016-10-10 10:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+---
+
+The default database that is used for Home Assistant is [SQLite](https://www.sqlite.org/) and is stored in your [configuration directory](/getting-started/configuration/), eg. `<path to config dir>/.homeassistant/home-assistant_v2.db`. You will need an installation of `sqlite3`, the command-line for SQLite database, or [DB Browser for SQLite](http://sqlitebrowser.org/) which provide an editor for executing SQL commands.
+First load your database with `sqlite3`.
+
+```bash
+$ sqlite3 home-assistant_v2.db 
+SQLite version 3.13.0 2016-05-18 10:57:30
+Enter ".help" for usage hints.
+sqlite> 
+```
+
+It helps to set some options to make the output better readable.
+
+```bash
+sqlite> .header on
+sqlite> .mode column
+```
+
+You could also start `sqlite3` and attach the database later. Not sure what database you are working with? Check it, especially if you are going to delete data.
+
+```bash
+sqlite> .databases
+seq  name             file
+---  ---------------  ----------------------------------------------------------
+0    main             /home/fab/.homeassistant/home-assistant_v2.db 
+```
+
+### {% linkable_title Schema %}
+
+Get all available tables from your current Home Assistant database.
+
+```bash
+sqlite> SELECT sql FROM sqlite_master;
+
+-------------------------------------------------------------------------------------
+CREATE TABLE events (
+	event_id INTEGER NOT NULL, 
+	event_type VARCHAR(32), 
+	event_data TEXT, 
+	origin VARCHAR(32), 
+	time_fired DATETIME, 
+	created DATETIME, 
+	PRIMARY KEY (event_id)
+)
+CREATE INDEX ix_events_event_type ON events (event_type)
+CREATE TABLE recorder_runs (
+	run_id INTEGER NOT NULL, 
+	start DATETIME, 
+	"end" DATETIME, 
+	closed_incorrect BOOLEAN, 
+	created DATETIME, 
+	PRIMARY KEY (run_id), 
+	CHECK (closed_incorrect IN (0, 1))
+)
+CREATE TABLE states (
+	state_id INTEGER NOT NULL, 
+	domain VARCHAR(64), 
+	entity_id VARCHAR(64), 
+	state VARCHAR(255), 
+	attributes TEXT, 
+	event_id INTEGER, 
+	last_changed DATETIME, 
+	last_updated DATETIME, 
+	created DATETIME, 
+	PRIMARY KEY (state_id), 
+	FOREIGN KEY(event_id) REFERENCES events (event_id)
+)
+CREATE INDEX states__significant_changes ON states (domain, last_updated, entity_id)
+CREATE INDEX states__state_changes ON states (last_changed, last_updated, entity_id)
+CREATE TABLE sqlite_stat1(tbl,idx,stat) 
+```
+
+To only show the details about the `states` table as we are using that one in the next examples.
+
+```bash
+sqlite> SELECT sql FROM sqlite_master WHERE type = 'table' AND tbl_name = 'states';
+```
+
+### {% linkable_title Query %}
+
+The identification of the available columns in the table is done and we are now able to create a query. Let's list of your Top 10 entities.
+
+```bash
+sqlite> .width 30, 10,
+sqlite> SELECT entity_id, COUNT(*) as count FROM states GROUP BY entity_id ORDER BY count DESC LIMIT 10;
+entity_id                       count
+------------------------------  ----------
+sensor.cpu                      28874
+sun.sun                         21238
+sensor.time                     18415
+sensor.new_york                 18393
+cover.kitchen_cover             17811
+switch.mystrom_switch           14101
+sensor.internet_time            12963
+sensor.solar_angle1             11397
+sensor.solar_angle              10440
+group.all_switches              8018 
+```
+
+### {% linkable_title Delete %}
+
+If you don't want to keep certain entities, you can delete them permanently.
+
+```bash
+sqlite> DELETE FROM states WHERE entity_id="sensor.cpu";
+```
+
+The `VACUUM` command cleans the your database.
+
+```bash
+sqlite> VACUUM;
+```
+
+For a more interactive way to work with the database or the create statistics, checkout our [Jupyther notebooks](http://nbviewer.jupyter.org/github/home-assistant/home-assistant-notebooks/blob/master/).
+