SQL UPPER

What does the SQL UPPER function do?

UPPER converts a character expression to all uppercase letters.

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Compatible dialects for SQL UPPER: Supported in PostgreSQL, MySQL, MariaDB, SQL Server, Oracle, SQLite, Snowflake, Redshift, BigQuery, DB2, Teradata

SQL UPPER Full Explanation

UPPER is a scalar string function that returns the input text with every alphabetic character converted to its uppercase form. Non alphabetic characters remain unchanged. The function is deterministic and collation-aware, meaning the exact result can depend on the database's locale and character set. UPPER is frequently used for case-insensitive searches, comparisons, data normalization, and display formatting. Because it creates a new string value, indexes on the original column are not used unless a functional or generated column index exists. Watch for performance impacts when calling UPPER on large text columns inside predicates or joins.

SQL UPPER Syntax

UPPER(expression);

SQL UPPER Parameters

expression (string or character expression) - The value to transform to uppercase.

Example Queries Using SQL UPPER

-- Normalize email addresses for comparison
SELECT email, UPPER(email) AS email_upper
FROM users;

-- Case-insensitive filter
SELECT *
FROM customers
WHERE UPPER(country) = 'CANADA';

-- Create a computed column
ALTER TABLE products ADD name_upper AS (UPPER(product_name));

Expected Output Using SQL UPPER

Each query returns the same text but with all alphabetic characters capitalized
In the WHERE clause example, only rows whose country equals 'Canada', 'CANADA', or any other case variation match

Use Cases with SQL UPPER

Make comparisons case-insensitive without changing stored data
Standardize data before loading into a warehouse
Build searchable text keys or computed columns
Display headings or codes in uppercase for UI consistency

Common Mistakes with SQL UPPER

Forgetting that UPPER can prevent index use, slowing queries
Using UPPER on already indexed columns inside WHERE without a functional index
Assuming UPPER changes non-alphabetic characters—it does not
Expecting locale-specific rules (e.g., Turkish dotted I) to behave identically across databases

First Introduced In

SQL-92

Frequently Asked Questions

How does SQL UPPER handle NULL values?

Returns NULL. Any NULL input yields NULL output.

Can I create an index that supports UPPER?

Yes. Most databases allow functional or generated column indexes. For example, in PostgreSQL: `CREATE INDEX idx_users_email_upper ON users (UPPER(email));`

Is UPPER affected by collation?

Yes. Collation determines how characters map to uppercase. Edge cases like Turkish dotted I may produce different results under different locales.

When should I avoid using UPPER?

Avoid it in large table predicates without supporting indexes, as it forces a full scan and may degrade performance.