HTTP endpoint

Table of contents

• Introduction

• Parameter substitution

• Default schema

• Column types

• Bulk operations

• Error handling

  • Bulk errors

Introduction

CrateDB provides a HTTP Endpoint that can be used to submit SQL queries. The endpoint is accessible under <servername:port>/_sql.

SQL statements are sent to the _sql endpoint in json format, whereby the statement is sent as value associated to the key stmt.

See also

Data manipulation

A simple SELECT statement can be submitted like this:

sh$ curl -sS -H 'Content-Type: application/json' \
... -X POST '127.0.0.1:4200/_sql' \
... -d '{"stmt":"select name, position from locations order by id limit 2"}'
{
  "cols": [
    "name",
    "position"
  ],
  "rows": [
    [
      "North West Ripple",
      1
    ],
    [
      "Outer Eastern Rim",
      2
    ]
  ],
  "rowcount": 2,
  "duration": ...
}

Note

We’re using a simple command line invokation of curl here so you can see how to run this by hand in the terminal. For the rest of the examples in this document, we use here documents (i.e. EOF) for multiline readability.

Parameter substitution

In addition to the stmt key the request body may also contain an args key which can be used for SQL parameter substitution.

The SQL statement has to be changed to use placeholders where the values should be inserted. Placeholders can either be numbered (in the form of $1, $2, etc.) or unnumbered using a question mark ?.

The placeholders will then be substituted with values from an array that is expected under the args key:

sh$ curl -sS -H 'Content-Type: application/json' \
... -X POST '127.0.0.1:4200/_sql' -d@- <<- EOF
... {
...   "stmt":
...     "select date,position from locations
...     where date <= \$1 and position < \$2 order by position",
...   "args": ["1979-10-12", 3]
... }
... EOF
{
  "cols": [
    "date",
    "position"
  ],
  "rows": [
    [
      308534400000,
      1
    ],
    [
      308534400000,
      2
    ]
  ],
  "rowcount": 2,
  "duration": ...
}

Note

In this example the placeholders start with an backslash due to shell escaping.

Warning

Parameter substitution must not be used within subscript notation.

For example, column[?] is not allowed.

The same query using question marks as placeholders looks like this:

sh$ curl -sS -H 'Content-Type: application/json' \
... -X POST '127.0.0.1:4200/_sql' -d@- <<- EOF
... {
...   "stmt":
...     "select date,position from locations
...     where date <= ? and position < ? order by position",
...   "args": ["1979-10-12", 3]
... }
... EOF
{
  "cols": [
    "date",
    "position"
  ],
  "rows": [
    [
      308534400000,
      1
    ],
    [
      308534400000,
      2
    ]
  ],
  "rowcount": 2,
  "duration": ...
}

Note

With some queries the row count is not ascertainable. In this cases rowcount is -1.

Default schema

It is possible to set a default schema while querying the CrateDB cluster via _sql end point. In such case the HTTP request should contain the Default-Schema header with the specified schema name:

sh$ curl -sS -H 'Content-Type: application/json' \
... -X POST '127.0.0.1:4200/_sql' \
... -H 'Default-Schema: doc' -d@- <<- EOF
... {
...   "stmt":"select name, position from locations order by id limit 2"
... }
... EOF
{
  "cols": [
    "name",
    "position"
  ],
  "rows": [
    [
      "North West Ripple",
      1
    ],
    [
      "Outer Eastern Rim",
      2
    ]
  ],
  "rowcount": 2,
  "duration": ...
}

If the schema name is not specified in the header, the default doc schema will be used instead.

Column types

CrateDB can respond a list col_types with the data type ID of every responded column. This way one can know what exact data type a column is holding.

In order to get the list of column data types, a types query parameter must be passed to the request:

sh$ curl -sS -H 'Content-Type: application/json' \
... -X POST '127.0.0.1:4200/_sql?types' -d@- <<- EOF
... {
...   "stmt":
...     "select date, position from locations
...      where date <= \$1 and position < \$2 order by position",
...   "args": ["1979-10-12", 3]
... }
... EOF
{
  "cols": [
    "date",
    "position"
  ],
  "col_types": [
    11,
    9
  ],
  "rows": [
    [
      308534400000,
      1
    ],
    [
      308534400000,
      2
    ]
  ],
  "rowcount": 2,
  "duration": ...
}

The Array collection data type is displayed as a list where the first value is the collection type and the second is the inner type. The inner type could also be a collection.

Example of JSON representation of a column list of (String, Integer[]):

"column_types": [ 4, [ 100, 9 ] ]

IDs of all currently available data types:

Bulk operations

The REST endpoint allows to issue bulk operations which are executed as single calls on the back-end site. It can be compared to prepared statement.

A bulk operation can be expressed simply as an SQL statement.

Supported bulk SQL statements are:

• Insert

• Update

• Delete

Instead of the args (Parameter substitution) key, use the key bulk_args. This allows to specify a list of lists, containing all the records which shall be processed. The inner lists need to match the specified columns.

The bulk response contains a results array, with a rowcount for each bulk operation. Those results are in the same order as the issued operations of the bulk operation.

The following example describes how to issue an insert bulk operation and insert three records at once:

sh$ curl -sS -H 'Content-Type: application/json' \
... -X POST '127.0.0.1:4200/_sql' -d@- <<- EOF
... {
...   "stmt": "INSERT INTO locations (id, name, kind, description)
...           VALUES (?, ?, ?, ?)",
...   "bulk_args": [
...     [1337, "Earth", "Planet", "An awesome place to spend some time on."],
...     [1338, "Sun", "Star", "An extraordinarily hot place."],
...     [1339, "Titan", "Moon", "Titan, where it rains fossil fuels."]
...   ]
... }
... EOF
{
  "cols": [],
  "duration": ...,
  "results": [
    {
      "rowcount": 1
    },
    {
      "rowcount": 1
    },
    {
      "rowcount": 1
    }
  ]
}

Error handling

Queries that are invalid or cannot be satisfied will result in an error response. The response will contain an error code, an error message and in some cases additional arguments that are specific to the error code.

Client libraries should use the error code to translate the error into an appropriate exception:

sh$ curl -sS -H 'Content-Type: application/json' \
... -X POST '127.0.0.1:4200/_sql' -d@- <<- EOF
... {
...   "stmt":"select name, position from foo.locations"
... }
... EOF
{
  "error": {
    "message": "SchemaUnknownException[Schema 'foo' unknown]",
    "code": 4045
  }
}

To get more insight into what exactly went wrong an additional error_trace GET parameter can be specified to return the stack trace:

sh$ curl -sS -H 'Content-Type: application/json' \
... -X POST '127.0.0.1:4200/_sql?error_trace=true' -d@- <<- EOF
... {
...   "stmt":"select name, position from foo.locations"
... }
... EOF
{
  "error": {
    "message": "SchemaUnknownException[Schema 'foo' unknown]",
    "code": 4045
  },
  "error_trace": "..."
}

Note

This parameter is intended for CrateDB developers or for users requesting support for CrateDB. Client libraries shouldn’t make use of this option and not include the stacktrace.

Currently the defined error codes are:

Bulk errors

If a bulk operation fails, the resulting rowcount will be -2 and the resulting object may contain an error_message depending on the resulting error:

sh$ curl -sS -H 'Content-Type: application/json' \
... -X POST '127.0.0.1:4200/_sql' -d@- <<- EOF
... {
...   "stmt": "INSERT into locations (name, id) values (?,?)",
...   "bulk_args": [
...     ["Mars", 1341],
...     ["Sun", 1341]
...   ]
... }
... EOF
{
  "cols": [],
  "duration": ...,
  "results": [
    {
      "rowcount": 1
    },
    {
      "rowcount": -2
    }
  ]
}

Note

Every bulk operation will be executed, independent if one of the operation fails.