SQL compatibility¶
CrateDB provides a standards-based SQL implementation similar to many other SQL databases. In particular, CrateDB aims for compatibility with PostgreSQL. However, CrateDB’s SQL dialect does have some unique characteristics, documented on this page.
See also
Table of contents
Implementation notes¶
Data types¶
CrateDB supports a set of primitive data types. The following table defines how data types of standard SQL map to CrateDB Data types.
Standard SQL |
CrateDB |
---|---|
integer |
integer, int, int4 |
bit[8] |
byte, char |
boolean, bool |
boolean |
char [(n)], varchar [(n)] |
string, text, varchar, character varying |
timestamp with time zone |
timestamp with time zone, timestamptz |
timestamp |
timestamp without time zone |
smallint |
short, int2, smallint |
bigint |
long, bigint, int8 |
real |
float, real |
double precision |
double, double precision |
Create table¶
CREATE TABLE supports additional storage and table parameters for sharding, replication and routing of data, and does not support inheritance.
Alter table¶
ALTER COLUMN
action is not currently supported (see ALTER TABLE).
System information tables¶
The read-only System information and Information schema tables have a slightly different schema than specified in standard SQL. They provide schema information and can be queried to get real-time statistical data about the cluster, its nodes, and their shards.
BLOB support¶
Standard SQL defines a binary string type, called BLOB
or BINARY LARGE
OBJECT
. With CrateDB, Binary Data is instead stored in separate BLOB Tables
(see Blobs) which can be sharded and replicated.
Transactions (BEGIN
, START
, COMMIT
, and ROLLBACK
)¶
CrateDB is focused on providing analytical capabilities over supporting traditional transactional use cases, and thus it does not provide transaction control. Every statement commits immediately and is replicated within the cluster.
However, every row in CrateDB has a version number that is incremented whenever the record is modified. This version number can be used to implement patterns like Optimistic Concurrency Control, which can be used to solve many of the use cases that would otherwise require traditional transactions.
Unsupported features and functions¶
These features of standard SQL are not supported:
Stored procedures
Triggers
Sequences
Inheritance
Constraints
Unique
Foreign key
Exclusion constraints
These functions of standard SQL are either not supported or only partly supported:
-
Various functions available (see Aggregation)
-
Various functions available (see Window functions)
ENUM
support functionsNetwork address functions and operators
Mathematical functions
Certain functions supported (see Mathematical functions)
Set returning functions
Trigger functions
XML functions
Note
The currently supported and unsupported features in CrateDB are exposed in the Information schema table (see sql_features for usage).
CrateDB also supports the PostgreSQL wire protocol.
If you have use cases for any missing features, functions, or dialect improvements, let us know on GitHub! We are always improving and extending CrateDB and would love to hear your feedback.