SETSEED

Set the seed for the pseudo-random number generator used by RANDOM().

Syntax

SETSEED(seed)

Description

## Overview Sets the seed of the session-local pseudo-random number generator used by RANDOM() and related functions. Once set, subsequent RANDOM() calls produce a deterministic sequence: the same seed always produces the same sequence until the next SETSEED or session end. SETSEED is the mechanism for reproducibility in tests and demonstrations: set the seed before a query that uses RANDOM(), and the output is stable. The seed is session-local and does not propagate across connections. ## Behavior - Accepts a single DOUBLE argument in the closed interval [-1.0, 1.0]. - Raises an error for inputs outside the valid range. - Returns void (no result set). Some engines return NULL as a placeholder. - Affects RANDOM() and any other function that shares the session's RNG state. - The seed persists for the remainder of the session unless overwritten. ## Numeric precision - The seed is interpreted as a 32-bit signed integer derived from the DOUBLE, so the effective seed space is coarser than the full DOUBLE precision. - Two seeds that round to the same underlying integer produce identical sequences. ## Compatibility - Matches the PostgreSQL SETSEED function, including the [-1.0, 1.0] input range. - Not a SQL standard function; other engines expose similar reseed primitives under different names.

Parameters

Name	Type	Description
seed		Specifies the seed value. Must be a DOUBLE in the closed interval [-1.0, 1.0]. Inputs outside this range raise an error.

Examples

-- Set a specific seed for reproducible results
SELECT SETSEED(0.42);

-- Set seed then generate a random number
SELECT SETSEED(0.5);
SELECT RANDOM();

-- Seed of zero
SELECT SETSEED(0.0);

-- Negative seed
SELECT SETSEED(-0.75);

-- Reseed inside a stored procedure or session to make a downstream SELECT deterministic
SELECT SETSEED(0.123);
SELECT trade_id, RANDOM() AS jitter
FROM finance.trades.orders
LIMIT 5;

Pitfalls

• SETSEED accepts only values in [-1.0, 1.0]. Passing a value outside that range raises an error, not a silent clamp. Normalize with (seed_int::DOUBLE / some_max_int) before calling.
• The seed is session-local. In a distributed query running on multiple workers, only the coordinator's seed may be affected; RANDOM() on a worker can still produce non-deterministic results.
• SETSEED must precede the RANDOM() call in the same session and same transaction. Ordering SETSEED after the RANDOM() call has no effect on that call.
• SETSEED does not guarantee reproducibility across engine versions. A seed that produces sequence A today may produce sequence B after an engine upgrade if the underlying RNG implementation changes.
• Avoid relying on SETSEED + RANDOM() for cryptographic purposes. Use a dedicated cryptographic random function instead.