CockroachDB supports the PostgreSQL wire protocol and the majority of PostgreSQL syntax. This means that existing applications built on PostgreSQL can often be migrated to CockroachDB without changing application code.
CockroachDB is compatible with version 3.0 of the PostgreSQL wire protocol (pgwire) and works with the majority of PostgreSQL database tools such as DBeaver, Intellij, and so on. Consult this link for a full list of supported third-party database tools. CockroachDB also works with most PostgreSQL drivers and ORMs.
However, CockroachDB does not support some of the PostgreSQL features or behaves differently from PostgreSQL because not all features can be easily implemented in a distributed system. This page documents the known list of differences between PostgreSQL and CockroachDB for identical input. That is, a SQL statement of the type listed here will behave differently than in PostgreSQL. Porting an existing application to CockroachDB will require changing these expressions.
This document currently only covers unsupported SQL and how to rewrite SQL expressions. It does not discuss strategies for porting applications that use SQL features CockroachDB does not currently support.
Unsupported Features
The following PostgreSQL features are not supported in CockroachDB v23.2:
- Triggers. These must be implemented in your application logic.
- Events.
Drop primary key.
Note:Each table must have a primary key associated with it. You can drop and add a primary key constraint within a single transaction.
XML functions.
Column-level privileges.
XA syntax.
Creating a database from a template.
Foreign data wrappers.
Advisory Lock Functions (although some functions are defined with no-op implementations).
Partially Supported Features
The following PostgreSQL features are partially supported in CockroachDB v23.2.
Multiple active portals
CockroachDB v23.2 supports pgwire's multiple active portals as a preview feature. The feature is off by default, and can be enabled by setting the session variable multiple_active_portals_enabled to true.
When set to true, multiple portals can be open at the same time, with their execution interleaved with each other. In other words, these portals can be paused.
This feature has the following limitations:
- Only read-only
SELECTqueries without subqueries are supported. - Postqueries (which are how CockroachDB executes foreign key checks, for example) are not supported - cockroachdb/cockroach#96398
- Distributed SQL execution is not supported for multiple active portals; instead queries execute on the gateway node only - cockroachdb/cockroach#100822
- Only the latest execution of a statement from a pausable portal is recorded by the trace infrastructure - cockroachdb/cockroach#99404
In addition to the known issues, additional performance testing is needed. The current list of known issues can be viewed on GitHub using the A-pausable-portals label, and we welcome bug reports.
Features that differ from PostgreSQL
Note, some of the differences below only apply to rare inputs, and so no change will be needed, even if the listed feature is being used. In these cases, it is safe to ignore the porting instructions.
Overflow of float
In PostgreSQL, the float type returns an error when it overflows or an expression would return Infinity:
postgres=# select 1e300::float * 1e10::float;
ERROR: value out of range: overflow
postgres=# select pow(0::float, -1::float);
ERROR: zero raised to a negative power is undefined
In CockroachDB, these expressions instead return Infinity:
SELECT 1e300::float * 1e10::float;
?column?
------------
+Inf
(1 row)
SELECT pow(0::float, -1::float);
pow
--------
+Inf
(1 row)
Precedence of unary ~
In PostgreSQL, the unary ~ (bitwise not) operator has a low precedence. For example, the following query is parsed as ~ (1 + 2) because ~ has a lower precedence than +:
SELECT ~1 + 2;
?column?
------------
0
(1 row)
In CockroachDB, unary ~ has the same (high) precedence as unary -, so the above expression will be parsed as (~1) + 2.
Porting instructions: Manually add parentheses around expressions that depend on the PostgreSQL behavior.
Precedence of bitwise operators
In PostgreSQL, the operators | (bitwise OR), # (bitwise XOR), and & (bitwise AND) all have the same precedence.
In CockroachDB, the precedence from highest to lowest is: &, #, |.
Porting instructions: Manually add parentheses around expressions that depend on the PostgreSQL behavior.
Integer division
In PostgreSQL, division of integers results in an integer. For example, the following query returns 1, since the 1 / 2 is truncated to 0:
SELECT 1 + 1 / 2;
?column?
------------
1.5
(1 row)
In CockroachDB, integer division results in a decimal. CockroachDB instead provides the // operator to perform floor division.
Porting instructions: Change / to // in integer division where the result must be an integer.
Shift argument modulo
In PostgreSQL, the shift operators (<<, >>) sometimes modulo their second argument to the bit size of the underlying type. For example, the following query results in a 1 because the int type is 32 bits, and 32 % 32 is 0, so this is the equivalent of 1 << 0:
SELECT 1::int << 32;
?column?
--------------
4294967296
(1 row)
In CockroachDB, no such modulo is performed.
Porting instructions: Manually add a modulo to the second argument. Also note that CockroachDB's INT type is always 64 bits. For example:
SELECT 1::int << (x % 64);
Locking and FOR UPDATE
CockroachDB supports the SELECT FOR UPDATE statement, which is used to order transactions by controlling concurrent access to one or more rows of a table.
For more information, see SELECT FOR UPDATE.
CHECK constraint validation for INSERT ON CONFLICT
CockroachDB validates CHECK constraints on the results of INSERT ON CONFLICT statements, preventing new or changed rows from violating the constraint. Unlike PostgreSQL, CockroachDB does not also validate CHECK constraints on the input rows of INSERT ON CONFLICT statements.
If this difference matters to your client, you can INSERT ON CONFLICT from a SELECT statement and check the inserted value as part of the SELECT. For example, instead of defining CHECK (x > 0) on t.x and using INSERT INTO t(x) VALUES (3) ON CONFLICT (x) DO UPDATE SET x = excluded.x, you could do the following:
> INSERT INTO t (x)
SELECT if (x <= 0, crdb_internal.force_error('23514', 'check constraint violated'), x)
FROM (values (3)) AS v(x)
ON CONFLICT (x)
DO UPDATE SET x = excluded.x;
An x value less than 1 would result in the following error:
pq: check constraint violated
Column name from an outer column inside a subquery
CockroachDB returns the column name from an outer column inside a subquery as ?column?, unlike PostgreSQL. For example:
> SELECT (SELECT t.*) FROM (VALUES (1)) t(x);
CockroachDB:
?column?
------------
1
PostgreSQL:
x
---
1
SQL Compatibility
Click the following link to find a full list of CockroachDB supported SQL Features.
Was this helpful?
