Querying Crate

This section provides an overview on how to query documents using SQL.

Retrieving Data

Retrieving data from Crate is done by using a SQL SELECT statement. The response to a SELECT query contains the column names of the result and the actual result rows as a two-dimensional array of values.

A simple select:

cr> select name, position from locations order by "_id" limit 2
+-------------------+----------+
| name              | position |
+-------------------+----------+
| North West Ripple | 1        |
| Arkintoofle Minor | 3        |
+-------------------+----------+

If the ‘*’ operator is used, all properties defined in the schema are returned for each object:

cr> select * from locations order by "_id" limit 1 offset 1
+--------------------------+--------------...---+--------+-------------------+----------+------+
| date                     | description        | kind   | name              | position | race |
+--------------------------+--------------...---+--------+-------------------+----------+------+
| 1979-10-12T00:00:00.000Z | Motivated by ...s. | Planet | Arkintoofle Minor | 3        | None |
+--------------------------+--------------...---+--------+-------------------+----------+------+

Aliases can be used to change the output name of the columns:

cr> select name as n from locations order by "_id" limit 1
+-------------------+
| n                 |
+-------------------+
| North West Ripple |
+-------------------+

Where Clause

A simple where clause example using an equality operator:

cr> select description from locations where "_id" = '1'
+-----------------------------------------...-------------------------------------------+
| description                                                                           |
+-----------------------------------------...-------------------------------------------+
| Relative to life on NowWhat, living on a...er by a factor of about seventeen million. |
+-----------------------------------------...-------------------------------------------+

Usual comparison operators to be used in filters are available for string, integer/long, float/double and date type:

Operator Description
< less than
> greater than
<= less than or equal to
>= greater than or equal to
= equal
<> not equal
!= not equal - same as <>
is not null field is not null and not missing
is null field is null or missing

Note

The field ‘name’ used for the request above is defined as ‘not_analyzed’ in the schema. For an ‘analyzed’ field the result may differ depending on the used Analyzer/Tokenizer. For details regarding analysis please refer to the elasticsearch analysis site.

For strings a lexicographical comparison is performed based on the Lucene TermRangeQuery:

cr> select name from locations where name > 'Argabuthon' order by name
+------------------------------------+
| name                               |
+------------------------------------+
| Arkintoofle Minor                  |
| Bartledan                          |
| Galactic Sector QQ7 Active J Gamma |
| North West Ripple                  |
| Outer Eastern Rim                  |
+------------------------------------+

For details please refer to the Apache Lucene site.

In most SQL databases there is a distinction between NULL and empty string. Since Crate is a schemaless document oriented database there is the third possibility that a row doesn’t contain a field. Due to this is null will return all rows where the fields value is NULL or where the field doesn’t exist at all. is not null also behaves this way. E.g. the following query returns 2 rows since the is null filter matches all rows and a limit is specified:

cr> select name from locations where missing is null order by "_id" limit 2
+-------------------+
| name              |
+-------------------+
| North West Ripple |
| Arkintoofle Minor |
+-------------------+

Number and date field comparison behave as expected from standard SQL. The following example uses one of the supported ISO date formats:

cr> select date, position from locations where date <= '1979-10-12' and
... position < 3 order by position
+--------------------------+----------+
| date                     | position |
+--------------------------+----------+
| 1979-10-12T00:00:00.000Z | 1        |
| 1979-10-12T00:00:00.000Z | 2        |
+--------------------------+----------+

All supported default ISO date formats are comparable. For a full list please refer to the elasticsearch date-format site.

For custom date types, or defined date formats in the object mapping the corresponding format should be used for a comparison. Otherwise the operation may fail.

Inner/Nested Objects

Crate supports an object data type, used for simple storing a whole object into a column and it’s even possible to select and query for properties of such objects.

Select a property of an inner object:

cr> select name, race['name'] from locations where name = 'Bartledan'
+-----------+----------------+
| name      | race['name']   |
+-----------+----------------+
| Bartledan | Bartledannians |
+-----------+----------------+

Query for a property of an inner object:

cr> select name, race['name'] from locations where race['name'] = 'bartledannians'
+-----------+----------------+
| name      | race['name']   |
+-----------+----------------+
| Bartledan | Bartledannians |
+-----------+----------------+

Inserting data

Inserting data to Crate is done by using the SQL INSERT statement.

Note

The column list at Crate is always ordered alphabetically by column name and so must the inserted column values.

Inserting a row:

cr> insert into locations values ('2013-09-12T21:43:59.000Z', 'Blagulon Kappa is the planet to which the police are native.', 'Planet', 'Blagulon Kappa', 7)

Inserting multiple rows at once (aka. bulk insert) can be done by defining multiple values for the INSERT statement:

cr> insert into locations (date, description, kind, name, position) values
... ('2013-09-12T21:43:59.000Z', 'Blagulon Kappa is the planet to which the police are native.', 'Planet', 'Blagulon Kappa', 7),
... ('2013-09-13T16:43:59.000Z', 'Brontitall is a planet with a warm, rich atmosphere and no mountains.', 'Planet', 'Brontitall', 10)

Deleting data

Deleting rows in Crate is done using the SQL DELETE statement:

cr> delete from locations where position > 3