ClickHouse lower Function

The lower function in ClickHouse is used to convert all characters in a string to lowercase. This function is particularly useful when you need to perform case-insensitive comparisons or standardize the case of string data in your queries.

Syntax

lower(string)

Official ClickHouse Documentation on lower function

Example usage

SELECT lower('Hello, World!') AS lowercase_text;

Result:

┌─lowercase_text─┐
│ hello, world!  │
└────────────────┘

Common issues

• The lower function only affects ASCII characters. For proper handling of Unicode characters, consider using the lowerUTF8 function instead.

Best practices

1. Use lower for case-insensitive comparisons in WHERE clauses or JOINs.
2. When working with non-ASCII text, prefer lowerUTF8 for accurate Unicode lowercase conversion.
3. Consider creating case-insensitive indexes on columns frequently used in searches by applying lower in the index definition.

Frequently Asked Questions

Q: What's the difference between lower and lowerUTF8 in ClickHouse?
A: lower only converts ASCII characters to lowercase, while lowerUTF8 handles Unicode characters correctly. Use lowerUTF8 for non-ASCII text.

Q: Can lower be used in index definitions?
A: Yes, you can use lower in index definitions to create case-insensitive indexes for faster searches.

Q: Does lower affect performance in large datasets?
A: While lower is generally fast, applying it to large columns in queries can impact performance. Consider pre-processing data or using functional indexes where appropriate.

Q: How can I combine lower with other string functions in ClickHouse?
A: You can nest lower within other functions or vice versa. For example: trim(lower(column_name)) to lowercase and trim a string.

Q: Is there an uppercase equivalent to the lower function in ClickHouse?
A: Yes, ClickHouse provides the `upper` function to convert strings to uppercase, which works similarly to lower.