# Sargable UPPER

Starting from [MariaDB 11.3](/docs/release-notes/community-server/old-releases/11.3/what-is-mariadb-113.md), expressions in the form

```sql
UPPER(key_col) = expr
UPPER(key_col) IN (constant-list)
```

are sargable if `key_col` uses either the `utf8mb3_general_ci` or `utf8mb4_general_ci` collation.

`UCASE` is a synonym for [UPPER](/docs/server/reference/sql-functions/string-functions/upper.md) so is covered as well.

Sargable means that the optimizer is able to use such conditions to construct access methods, estimate their selectivity, or perform partition pruning.

## Example

```sql
CREATE TABLE t1 (
  key1 VARCHAR(32) COLLATE utf8mb4_general_ci,
  ...
  KEY(key1)
);
```

```sql
EXPLAIN SELECT * FROM t1 WHERE UPPER(key1)='ABC'
+------+-------------+-------+------+---------------+------+---------+-------+------+--------------------------+
| id   | select_type | table | type | possible_keys | key  | key_len | ref   | rows | Extra                    |
+------+-------------+-------+------+---------------+------+---------+-------+------+--------------------------+
|    1 | SIMPLE      | t1    | ref  | key1          | key1 | 131     | const | 1    | Using where; Using index |
+------+-------------+-------+------+---------------+------+---------+-------+------+--------------------------+
```

Note that `ref` access is used.

An example with join:

```sql
EXPLAIN SELECT * FROM t0,t1 WHERE upper(t1.key1)=t0.col;
+------+-------------+-------+------+---------------+------+---------+-------------+------+-------------+
| id   | select_type | table | type | possible_keys | key  | key_len | ref         | rows | Extra       |
+------+-------------+-------+------+---------------+------+---------+-------------+------+-------------+
|    1 | SIMPLE      | t0    | ALL  | NULL          | NULL | NULL    | NULL        | 10   | Using where |
|    1 | SIMPLE      | t1    | ref  | key1          | key1 | 131     | test.t0.col | 1    | Using index |
+------+-------------+-------+------+---------------+------+---------+-------------+------+-------------+
```

Here, the optimizer was able to construct `ref` access.

## Controlling the Optimization

The [optimizer\_switch](/docs/server/ha-and-performance/optimization-and-tuning/query-optimizations/optimizer-switch.md) variable has the flag `sargable_casefold` to turn the optimization on and off. The default is ON.

## Optimizer Trace

The optimization is implemented as a rewrite for a query's WHERE/ON conditions. It uses the `sargable_casefold_removal` object name in the trace:

```json
"join_optimization": {
        "select_id": 1,
        "steps": [
          {
            "sargable_casefold_removal": {
              "before": "ucase(t1.key1) = t0.col",
              "after": "t1.key1 = t0.col"
            }
          },
```

## References

* [MDEV-31496](https://jira.mariadb.org/browse/MDEV-31496): Make optimizer handle UCASE(varchar\_col)=...
* An analog for [LCASE](/docs/server/reference/sql-functions/string-functions/lcase.md) is not possible. See [MDEV-31955](https://jira.mariadb.org/browse/MDEV-31955): Make optimizer handle LCASE(varchar\_col)=... for details.

<sub>*This page is licensed: CC BY-SA / Gnu FDL*</sub>

{% @marketo/form formId="4316" %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://mariadb.com/docs/server/ha-and-performance/optimization-and-tuning/query-optimizations/sargable-upper.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.