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docs/en/sql-reference/functions/array-functions.md
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@ -102,6 +102,8 @@ The function also works for strings.
Can be optimized by enabling the [optimize_functions_to_subcolumns](../../operations/settings/settings.md#optimize-functions-to-subcolumns) setting. With `optimize_functions_to_subcolumns = 1` the function reads only [size0](../../sql-reference/data-types/array.md#array-size) subcolumn instead of reading and processing the whole array column. The query `SELECT length(arr) FROM table` transforms to `SELECT arr.size0 FROM TABLE`.
Alias: `OCTET_LENGTH`
## emptyArrayUInt8, emptyArrayUInt16, emptyArrayUInt32, emptyArrayUInt64
## emptyArrayInt8, emptyArrayInt16, emptyArrayInt32, emptyArrayInt64

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docs/en/sql-reference/functions/string-functions.md
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@ -90,6 +90,8 @@ Returns the length of a string in bytes (not: in characters or Unicode code poin
The function also works for arrays.
Alias: `OCTET_LENGTH`
## lengthUTF8
Returns the length of a string in Unicode code points (not: in bytes or characters). It assumes that the string contains valid UTF-8 encoded text. If this assumption is violated, no exception is thrown and the result is undefined.