PostgreSQL Compatibility

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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 Postgres 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.

Unsupported Features

Unsupported PostgreSQL features

The following PostgreSQL features are not supported in CockroachDB v21.1:

• Stored procedures and functions
• Triggers
• Events
• User-defined functions (UDF)
• FULLTEXT functions and indexes
• Drop primary key*
• XML Functions
• Column-level privileges
• XA syntax
• Creating a database from a template
• Dropping a single partition from a table

* Each table must have a primary key associated with it. You can, however, drop and add a primary key constraint within a single transaction.

Unsupported PostgreSQL wire protocol features

The following features of the PostgreSQL wire protocol are not supported in CockroachDB v21.1:

• Multiple active portals
• Query cancellation

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

Tracking GitHub Issue

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

Tracking GitHub Issue

SQL Compatibility

Click the following link to find a full list of CockroachDB supported SQL Features.

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