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 thelowerUTF8
function instead.
Best practices
- Use
lower
for case-insensitive comparisons in WHERE clauses or JOINs. - When working with non-ASCII text, prefer
lowerUTF8
for accurate Unicode lowercase conversion. - 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
.