TIMESTAMP predicate incorrectly matches rows with higher fractional seconds

[fengys1996]

What type of bug is this?

Incorrect result

What subsystems are affected?

Query Engine

Minimal reproduce step

1. start greptimedb in standalone mode.

2. create table

CREATE TABLE ts_precision_bug (
    ts TIMESTAMP(3) TIME INDEX,
    v INT,
    PRIMARY KEY (v)
);

3. insert data

INSERT INTO ts_precision_bug VALUES
    ('2026-06-02 03:49:59.999', 1),
    ('2026-06-02 03:50:00.000', 2),
    ('2026-06-02 03:50:00.195', 3),
    ('2026-06-02 03:50:01.000', 4);

4. query data

SELECT ts, v
FROM ts_precision_bug
WHERE ts <= '2026-06-02 03:50:00'
ORDER BY ts DESC
LIMIT 1;

What did you expect to see?

+-------------------------+------+
| ts                      | v    |
+-------------------------+------+
| 2026-06-02 03:50:00.000 | 2    |
+-------------------------+------+

What did you see instead?

+-------------------------+------+
| ts                      | v    |
+-------------------------+------+
| 2026-06-02 03:50:00.195 | 3    |
+-------------------------+------+

What operating system did you use?

arch linux

What version of GreptimeDB did you use?

v1.0.2

Relevant log output and stack trace

[discord9]

could be related to apache/datafusion#21908

[fengys1996]

The root cause may be that the timestamp literal is inferred with lower precision. (by codex)

Flow:

ts <= '2026-06-02 03:50:00'

GreptimeDB TypeConversionRule parses the string as:

TimestampSecond('2026-06-02 03:50:00')

Then DataFusion TypeCoercion compares a TimestampMillisecond column with a TimestampSecond literal and chooses the coarser Second unit as the common type, downcasting the column:

CAST(ts AS TimestampSecond) <= TimestampSecond(...)

Later, ConstNormalizationRule preserves that semantics and rewrites it to:

ts < '2026-06-02 03:50:01.000'

So 2026-06-02 03:50:00.195 is included.

The root cause is not ConstNormalizationRule or unwrap_cast; it is that the string timestamp literal is not converted using the timestamp column’s precision.

[fengys1996]

Related to apache/datafusion#22756