{"id": "sql_queries:id2", "page": "sql_queries", "ref": "id2", "title": "Pagination", "content": "Datasette's default table pagination is designed to be extremely efficient. SQL OFFSET/LIMIT pagination can have a significant performance penalty once you get into multiple thousands of rows, as each page still requires the database to scan through every preceding row to find the correct offset. \n             When paginating through tables, Datasette instead orders the rows in the table by their primary key and performs a WHERE clause against the last seen primary key for the previous page. For example: \n             select rowid, * from Tree_List where rowid > 200 order by rowid limit 101 \n             This represents page three for this particular table, with a page size of 100. \n             Note that we request 101 items in the limit clause rather than 100. This allows us to detect if we are on the last page of the results: if the query returns less than 101 rows we know we have reached the end of the pagination set. Datasette will only return the first 100 rows - the 101st is used purely to detect if there should be another page. \n             Since the where clause acts against the index on the primary key, the query is extremely fast even for records that are a long way into the overall pagination set.", "breadcrumbs": "[\"Running SQL queries\"]", "references": "[]"}
{"id": "sql_queries:sql-views", "page": "sql_queries", "ref": "sql-views", "title": "Views", "content": "If you want to bundle some pre-written SQL queries with your Datasette-hosted database you can do so in two ways. The first is to include SQL views in your database - Datasette will then list those views on your database index page. \n             The quickest way to create views is with the SQLite command-line interface: \n             sqlite3 sf-trees.db \n             SQLite version 3.19.3 2017-06-27 16:48:08\nEnter \".help\" for usage hints.\nsqlite> CREATE VIEW demo_view AS select qSpecies from Street_Tree_List;\n<CTRL+D> \n             You can also use the  sqlite-utils  tool to  create a view : \n             sqlite-utils create-view sf-trees.db demo_view \"select qSpecies from Street_Tree_List\"", "breadcrumbs": "[\"Running SQL queries\"]", "references": "[{\"href\": \"https://sqlite-utils.datasette.io/\", \"label\": \"sqlite-utils\"}, {\"href\": \"https://sqlite-utils.datasette.io/en/stable/cli.html#creating-views\", \"label\": \"create a view\"}]"}
{"id": "sql_queries:canned-queries-magic-parameters", "page": "sql_queries", "ref": "canned-queries-magic-parameters", "title": "Magic parameters", "content": "Named parameters that start with an underscore are special: they can be used to automatically add values created by Datasette that are not contained in the incoming form fields or query string. \n                 These magic parameters are only supported for canned queries: to avoid security issues (such as queries that extract the user's private cookies) they are not available to SQL that is executed by the user as a custom SQL query. \n                 Available magic parameters are: \n                 \n                     \n                         _actor_*  - e.g.  _actor_id ,  _actor_name \n                         \n                             Fields from the currently authenticated  Actors . \n                         \n                     \n                     \n                         _header_*  - e.g.  _header_user_agent \n                         \n                             Header from the incoming HTTP request. The key should be in lower case and with hyphens converted to underscores e.g.  _header_user_agent  or  _header_accept_language . \n                         \n                     \n                     \n                         _cookie_*  - e.g.  _cookie_lang \n                         \n                             The value of the incoming cookie of that name. \n                         \n                     \n                     \n                         _now_epoch \n                         \n                             The number of seconds since the Unix epoch. \n                         \n                     \n                     \n                         _now_date_utc \n                         \n                             The date in UTC, e.g.  2020-06-01 \n                         \n                     \n                     \n                         _now_datetime_utc \n                         \n                             The ISO 8601 datetime in UTC, e.g.  2020-06-24T18:01:07Z \n                         \n                     \n                     \n                         _random_chars_*  - e.g.  _random_chars_128 \n                         \n                             A random string of characters of the specified length. \n                         \n                     \n                 \n                 Here's an example configuration that adds a message from the authenticated user, storing various pieces of additional metadata using magic parameters: \n                 [[[cog\nconfig_example(cog, \"\"\"\ndatabases:\n  mydatabase:\n    queries:\n      add_message:\n        allow:\n          id: \"*\"\n        sql: |-\n          INSERT INTO messages (\n            user_id, message, datetime\n          ) VALUES (\n            :_actor_id, :message, :_now_datetime_utc\n          )\n        write: true\n\"\"\") \n                 ]]] \n                 [[[end]]] \n                 The form presented at  /mydatabase/add_message  will have just a field for  message  - the other parameters will be populated by the magic parameter mechanism. \n                 Additional custom magic parameters can be added by plugins using the  register_magic_parameters(datasette)  hook.", "breadcrumbs": "[\"Running SQL queries\", \"Canned queries\"]", "references": "[]"}
{"id": "sql_queries:id3", "page": "sql_queries", "ref": "id3", "title": "Cross-database queries", "content": "SQLite has the ability to run queries that join across multiple databases. Up to ten databases can be attached to a single SQLite connection and queried together. \n             Datasette can execute joins across multiple databases if it is started with the  --crossdb  option: \n             datasette fixtures.db extra_database.db --crossdb \n             If it is started in this way, the  /_memory  page can be used to execute queries that join across multiple databases. \n             References to tables in attached databases should be preceded by the database name and a period. \n             For example, this query will show a list of tables across both of the above databases: \n             select\n  'fixtures' as database, *\nfrom\n  [fixtures].sqlite_master\nunion\nselect\n  'extra_database' as database, *\nfrom\n  [extra_database].sqlite_master \n             Try that out here .", "breadcrumbs": "[\"Running SQL queries\"]", "references": "[{\"href\": \"https://latest.datasette.io/_memory?sql=select%0D%0A++%27fixtures%27+as+database%2C+*%0D%0Afrom%0D%0A++%5Bfixtures%5D.sqlite_master%0D%0Aunion%0D%0Aselect%0D%0A++%27extra_database%27+as+database%2C+*%0D%0Afrom%0D%0A++%5Bextra_database%5D.sqlite_master\", \"label\": \"Try that out here\"}]"}
{"id": "sql_queries:fragment", "page": "sql_queries", "ref": "fragment", "title": "fragment", "content": "Some plugins, such as  datasette-vega , can be configured by including additional data in the fragment hash of the URL - the bit that comes after a  #  symbol. \n                     You can set a default fragment hash that will be included in the link to the canned query from the database index page using the  \"fragment\"  key. \n                     This example demonstrates both  fragment  and  hide_sql : \n                     [[[cog\nconfig_example(cog, \"\"\"\ndatabases:\n  fixtures:\n    queries:\n      neighborhood_search:\n        fragment: fragment-goes-here\n        hide_sql: true\n        sql: |-\n          select neighborhood, facet_cities.name, state\n          from facetable join facet_cities on facetable.city_id = facet_cities.id\n          where neighborhood like '%' || :text || '%' order by neighborhood;\n\"\"\") \n                     ]]] \n                     [[[end]]] \n                     See here  for a demo of this in action.", "breadcrumbs": "[\"Running SQL queries\", \"Canned queries\", \"Additional canned query options\"]", "references": "[{\"href\": \"https://github.com/simonw/datasette-vega\", \"label\": \"datasette-vega\"}, {\"href\": \"https://latest.datasette.io/fixtures#queries\", \"label\": \"See here\"}]"}
{"id": "sql_queries:canned-queries-json-api", "page": "sql_queries", "ref": "canned-queries-json-api", "title": "JSON API for writable canned queries", "content": "Writable canned queries can also be accessed using a JSON API. You can POST data to them using JSON, and you can request that their response is returned to you as JSON. \n                 To submit JSON to a writable canned query, encode key/value parameters as a JSON document: \n                 POST /mydatabase/add_message\n\n{\"message\": \"Message goes here\"} \n                 You can also continue to submit data using regular form encoding, like so: \n                 POST /mydatabase/add_message\n\nmessage=Message+goes+here \n                 There are three options for specifying that you would like the response to your request to return JSON data, as opposed to an HTTP redirect to another page. \n                 \n                     \n                         Set an  Accept: application/json  header on your request \n                     \n                     \n                         Include  ?_json=1  in the URL that you POST to \n                     \n                     \n                         Include  \"_json\": 1  in your JSON body, or  &_json=1  in your form encoded body \n                     \n                 \n                 The JSON response will look like this: \n                 {\n    \"ok\": true,\n    \"message\": \"Query executed, 1 row affected\",\n    \"redirect\": \"/data/add_name\"\n} \n                 The  \"message\"  and  \"redirect\"  values here will take into account  on_success_message ,  on_success_message_sql ,   on_success_redirect ,  on_error_message  and  on_error_redirect , if they have been set.", "breadcrumbs": "[\"Running SQL queries\", \"Canned queries\"]", "references": "[]"}