Runtime decoding error when mapping MariaDB `YEAR`/`SMALLINT` to `u16` using `query_as!`

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I encountered an unexpected runtime decoding error while using sqlx::query_as! with MariaDB.

The application compiled successfully, but at runtime failed with:

error occurred while decoding column N:
out of range integral type conversion attempted

The affected column was either a MariaDB YEAR or SMALLINT column mapped to a Rust u16.

At the time the issue occurred, adding the following derives to the destination struct made the runtime error disappear:

#[derive(Debug, Serialize, ToSchema, Clone, sqlx::FromRow)]

Although query_as! should not require FromRow, and neither Clone nor FromRow should affect primitive value decoding, the behavior changed after adding these derives.

Unfortunately, I have not yet been able to construct a minimal reproducible example, so I cannot determine whether these derives are the root cause or whether they only changed the generated code path.

Query

sqlx::query_as!(
    Class,
    "SELECT id, major_id, name, enrollment_year, created_at, updated_at
     FROM classes
     WHERE id = ?",
    id
)
.fetch_one(pool)
.await

Expected Behavior

The runtime decoding behavior of query_as! should not depend on unrelated derives such as Clone or sqlx::FromRow.

Notes

I understand that this report is currently incomplete because I cannot provide a reliable minimal reproduction.

I'm opening this issue mainly to ask whether this behavior is already known or whether there are existing issues involving MariaDB, query_as!, and decoding YEAR/SMALLINT into u16.

If needed, I'd be happy to continue investigating and provide a minimal reproducible example.

Description

I encountered an unexpected decoding issue when using sqlx::query_as! with MariaDB.

When selecting a YEAR or SMALLINT column into a Rust u16 field, the query fails with:

error occurred while decoding column N:
out of range integral type conversion attempted

However, after deriving both:

#[derive(sqlx::FromRow, Clone)]

for the destination struct, the exact same query succeeds without changing:

• SQL
• database schema
• database contents
• field types

This behavior is unexpected because query_as! should not require FromRow, and Clone should not affect primitive value decoding.

I understand that this report is currently incomplete because I cannot provide a reliable minimal reproduction.

I'm opening this issue mainly to ask whether this behavior is already known or whether there are existing issues involving MariaDB, query_as!, and decoding YEAR/SMALLINT into u16.

If needed, I'd be happy to continue investigating and provide a minimal reproducible example.

Reproduction steps

The destination struct was similar to:

type Id = u64;
#[derive(Debug, Serialize, ToSchema)]
pub struct Class {
    pub id: Id,
    pub major_id: Id,
    pub name: String,
    pub enrollment_year: u16,
    pub created_at: OffsetDateTime,
    pub updated_at: OffsetDateTime,
}

After changing it to:

type Id = u64;
#[derive(Debug, Serialize, ToSchema, Clone, sqlx::FromRow)]
pub struct Class {
    pub id: Id,
    pub major_id: Id,
    pub name: String,
    pub enrollment_year: u16,
    pub created_at: OffsetDateTime,
    pub updated_at: OffsetDateTime,
}

the runtime error disappeared.

SQLx version

0.8.6

Enabled SQLx features

mysql, runtime-tokio, macros, time

Database server and version

10.6.23-MariaDB-0ubuntu0.22.04.1

Operating system

ArchLinux

Rust version

rustc 1.91.1 (ed61e7d7e 2025-11-07)