Round a numeric value using Python / IEEE 754 semantics (round half to even).
PYTHON_ROUND(expr, d)## Overview Returns the input rounded to the specified number of decimal places using round-half-to-even semantics, matching Python's built-in round() function on floats. The behavior is identical to BROUND except that the scale argument is mandatory, eliminating ambiguity when callers port code from Python. Use PYTHON_ROUND when you need bit-for-bit reproducibility with a Python data pipeline that consumes the SQL output. For general banker's-rounding workloads where the default scale of 0 is acceptable, BROUND is usually more convenient. ## Behavior - Both arguments are required. - Returns NULL if either argument is NULL. - Uses round-half-to-even: 2.5 -> 2, 3.5 -> 4, 2.45 -> 2.4, 2.35 -> 2.4. - Negative scale rounds to the left of the decimal point. - Matches Python's round() behavior on DOUBLE inputs exactly, including the surprises caused by binary floating-point representation. ## Numeric precision - For DECIMAL inputs, rounding is exact. - For DOUBLE inputs, the binary representation of values like 2.675 can cause round-half-to-even to select the 'wrong' neighbor. This is intentional: the goal of PYTHON_ROUND is to match Python, which has the same behavior. - Pair with DECIMAL storage for exact decimal rounding. ## Compatibility - Matches Python's round() function on floats exactly. - Implements the IEEE 754 default rounding mode (round half to even).
| Name | Type | Description |
|---|---|---|
expr | Specifies the numeric value to round. Accepts any numeric type. | |
d | Specifies the number of decimal places. Required (unlike ROUND and BROUND, there is no default). Negative values round to the left of the decimal point. |
-- Halfway rounds to even: 2.5 rounds to 2
SELECT PYTHON_ROUND(2.5, 0);
-- Result: 2.0-- Halfway rounds to even: 3.5 rounds to 4
SELECT PYTHON_ROUND(3.5, 0);
-- Result: 4.0-- Round to 2 decimal places (note floating-point representation surprises)
SELECT PYTHON_ROUND(2.675, 2);
-- Result: 2.67-- Negative decimal places
SELECT PYTHON_ROUND(125, -1);
-- Result: 120.0-- NULL propagation
SELECT PYTHON_ROUND(NULL, 2);
-- Result: NULL-- Column use: match a downstream Python pipeline's rounding exactly
SELECT event_id, PYTHON_ROUND(metric_value, 4) AS rounded_metric
FROM analytics.ml.evaluation_metrics;