Impala String Functions String Functions

String functions are classified as those primarily accepting or returning STRING, VARCHAR, or CHAR data types, for example to measure the length of a string or concatenate two strings together.

The string functions operate mainly on these data types: , , and .

Function reference:

Impala supports the following string functions:

ASCII(STRING str)
Purpose: Returns the numeric ASCII code of the first character of the argument.

Return type: INT

BASE64DECODE(STRING str)
Purpose:

Return type: STRING

For general information about Base64 encoding, see .

BASE64ENCODE(STRING str)
Purpose:

Return type: STRING

For general information about Base64 encoding, see .

BTRIM(STRING a), BTRIM(STRING a, STRING chars_to_trim)
Purpose: Removes all instances of one or more characters from the start and end of a STRING value. By default, removes only spaces. If a non-NULL optional second argument is specified, the function removes all occurrences of characters in that second argument from the beginning and end of the string.

Return type: STRING

The following examples show the default BTRIM() behavior, and what changes when you specify the optional second argument. All the examples bracket the output value with [ ] so that you can see any leading or trailing spaces in the BTRIM() result. By default, the function removes and number of both leading and trailing spaces. When the second argument is specified, any number of occurrences of any character in the second argument are removed from the start and end of the input string; in this case, spaces are not removed (unless they are part of the second argument) and any instances of the characters are not removed if they do not come right at the beginning or end of the string.

-- Remove multiple spaces before and one space after. select concat('[',btrim(' hello '),']'); +---------------------------------------+ | concat('[', btrim(' hello '), ']') | +---------------------------------------+ | [hello] | +---------------------------------------+ -- Remove any instances of x or y or z at beginning or end. Leave spaces alone. select concat('[',btrim('xy hello zyzzxx','xyz'),']'); +------------------------------------------------------+ | concat('[', btrim('xy hello zyzzxx', 'xyz'), ']') | +------------------------------------------------------+ | [ hello ] | +------------------------------------------------------+ -- Remove any instances of x or y or z at beginning or end. -- Leave x, y, z alone in the middle of the string. select concat('[',btrim('xyhelxyzlozyzzxx','xyz'),']'); +----------------------------------------------------+ | concat('[', btrim('xyhelxyzlozyzzxx', 'xyz'), ']') | +----------------------------------------------------+ | [helxyzlo] | +----------------------------------------------------+
CHAR_LENGTH(STRING a), CHARACTER_LENGTH(STRING a)
Purpose: Returns the length in characters of the argument string, including any trailing spaces that pad a CHAR value.

Return type: INT

When applied to a STRING value, it returns the same result as the length() function. When applied to a CHAR value, it might return a larger value than length() does, to account for trailing spaces in the CHAR.

CHR(INT character_code)
Purpose: Returns a character specified by a decimal code point value. The interpretation and display of the resulting character depends on your system locale. Because consistent processing of Impala string values is only guaranteed for values within the ASCII range, only use this function for values corresponding to ASCII characters. In particular, parameter values greater than 255 return an empty string.

Return type: STRING

Usage notes: Can be used as the inverse of the ascii() function, which converts a character to its numeric ASCII code.

SELECT chr(65); +---------+ | chr(65) | +---------+ | A | +---------+ SELECT chr(97); +---------+ | chr(97) | +---------+ | a | +---------+

CONCAT(STRING a, STRING b...)
Purpose: Returns a single string representing all the argument values joined together.

Return type: STRING

CONCAT_WS(STRING sep, STRING a, STRING b...)
Purpose: Returns a single string representing the second and following argument values joined together, delimited by a specified separator.

Return type: STRING

FIND_IN_SEt(STRING str, STRING strList)
Purpose: Returns the position (starting from 1) of the first occurrence of a specified string within a comma-separated string. Returns NULL if either argument is NULL, 0 if the search string is not found, or 0 if the search string contains a comma.

Return type: INT

GROUP_CONCAT(STRING s [, STRING sep])
Purpose: Returns a single string representing the argument value concatenated together for each row of the result set. If the optional separator string is specified, the separator is added between each pair of concatenated values.

Return type: STRING

By default, returns a single string covering the whole result set. To include other columns or values in the result set, or to produce multiple concatenated strings for subsets of rows, include a GROUP BY clause in the query.

Strictly speaking, GROUP_CONCAT() is an aggregate function, not a scalar function like the others in this list. For additional details and examples, see .

INITCAP(STRING str)
Purpose: Returns the input string with the first letter capitalized.

Return type: STRING

INSTR(STRING str, STRING substr [, BIGINT position [, BIGINT occurrence ] ])
Purpose: Returns the position (starting from 1) of the first occurrence of a substring within a longer string.

Return type: INT

If the substring is not present in the string, the function returns 0:

select instr('foo bar bletch', 'z'); +------------------------------+ | instr('foo bar bletch', 'z') | +------------------------------+ | 0 | +------------------------------+

The optional third and fourth arguments let you find instances of the substring other than the first instance starting from the left:

  • The third argument lets you specify a starting point within the string other than 1:

    -- Restricting the search to positions 7..end, -- the first occurrence of 'b' is at position 9. select instr('foo bar bletch', 'b', 7); +---------------------------------+ | instr('foo bar bletch', 'b', 7) | +---------------------------------+ | 9 | +---------------------------------+ -- If there are no more occurrences after the -- specified position, the result is 0. select instr('foo bar bletch', 'b', 10); +----------------------------------+ | instr('foo bar bletch', 'b', 10) | +----------------------------------+ | 0 | +----------------------------------+

    If the third argument is negative, the search works right-to-left starting that many characters from the right. The return value still represents the position starting from the left side of the string.

    -- Scanning right to left, the first occurrence of 'o' -- is at position 8. (8th character from the left.) select instr('hello world','o',-1); +-------------------------------+ | instr('hello world', 'o', -1) | +-------------------------------+ | 8 | +-------------------------------+ -- Scanning right to left, starting from the 6th character -- from the right, the first occurrence of 'o' is at -- position 5 (5th character from the left). select instr('hello world','o',-6); +-------------------------------+ | instr('hello world', 'o', -6) | +-------------------------------+ | 5 | +-------------------------------+ -- If there are no more occurrences after the -- specified position, the result is 0. select instr('hello world','o',-10); +--------------------------------+ | instr('hello world', 'o', -10) | +--------------------------------+ | 0 | +--------------------------------+

  • The fourth argument lets you specify an occurrence other than the first:

    -- 2nd occurrence of 'b' is at position 9. select instr('foo bar bletch', 'b', 1, 2); +------------------------------------+ | instr('foo bar bletch', 'b', 1, 2) | +------------------------------------+ | 9 | +------------------------------------+ -- Negative position argument means scan right-to-left. -- This example finds second instance of 'b' from the right. select instr('foo bar bletch', 'b', -1, 2); +-------------------------------------+ | instr('foo bar bletch', 'b', -1, 2) | +-------------------------------------+ | 5 | +-------------------------------------+

    If the fourth argument is greater than the number of matching occurrences, the function returns 0:

    -- There is no 3rd occurrence within the string. select instr('foo bar bletch', 'b', 1, 3); +------------------------------------+ | instr('foo bar bletch', 'b', 1, 3) | +------------------------------------+ | 0 | +------------------------------------+ -- There is not even 1 occurrence when scanning -- the string starting at position 10. select instr('foo bar bletch', 'b', 10, 1); +-------------------------------------+ | instr('foo bar bletch', 'b', 10, 1) | +-------------------------------------+ | 0 | +-------------------------------------+

    The fourth argument cannot be negative or zero. A non-positive value for this argument causes an error:

    select instr('foo bar bletch', 'b', 1, 0); ERROR: UDF ERROR: Invalid occurrence parameter to instr function: 0 select instr('aaaaaaaaa','aa', 1, -1); ERROR: UDF ERROR: Invalid occurrence parameter to instr function: -1

  • If either of the optional arguments is NULL, the function also returns NULL:

    select instr('foo bar bletch', 'b', null); +------------------------------------+ | instr('foo bar bletch', 'b', null) | +------------------------------------+ | NULL | +------------------------------------+ select instr('foo bar bletch', 'b', 1, null); +---------------------------------------+ | instr('foo bar bletch', 'b', 1, null) | +---------------------------------------+ | NULL | +---------------------------------------+
LEFT(STRING a, INT num_chars)
See the STRLEFT() function.
LENGTH(STRING a)
Purpose: Returns the length in characters of the argument string, ignoring any trailing spaces in CHAR values.

Return type: INT

When applied to a STRING value, it returns the same result as the CHAR_LENGTH() function. When applied to a CHAR value, it might return a smaller value than CHAR_LENGTH() does, because LENGTH() ignores any trailing spaces in the CHAR.

Because the behavior of LENGTH() with CHAR values containing trailing spaces is not standardized across the industry, when porting code from other database systems, evaluate the behavior of LENGTH() on the source system and switch to CHAR_LENGTH() for Impala if necessary.

LOCATE(STRING substr, STRING str[, INT pos])
Purpose: Returns the position (starting from 1) of the first occurrence of a substring within a longer string, optionally after a particular position.

Return type: INT

LOWER(STRING a), LCASE(STRING a)
Purpose: Returns the argument string converted to all-lowercase.

Return type: STRING

LPAD(STRING str, INT len, STRING pad)
Purpose: Returns a string of a specified length, based on the first argument string. If the specified string is too short, it is padded on the left with a repeating sequence of the characters from the pad string. If the specified string is too long, it is truncated on the right.

Return type: STRING

LTRIM(STRING a [, STRING chars_to_trim])
Purpose: Returns the argument string with all occurrences of characters specified by the second argument removed from the left side. Removes spaces if the second argument is not specified.

Return type: STRING

PARSE_URL(STRING urlString, STRING partToExtract [, STRING keyToExtract])
parse_url() function Purpose: Returns the portion of a URL corresponding to a specified part. The part argument can be 'PROTOCOL', 'HOST', 'PATH', 'REF', 'AUTHORITY', 'FILE', 'USERINFO', or 'QUERY'. Uppercase is required for these literal values. When requesting the QUERY portion of the URL, you can optionally specify a key to retrieve just the associated value from the key-value pairs in the query string.

Return type: STRING

Usage notes: This function is important for the traditional Hadoop use case of interpreting web logs. For example, if the web traffic data features raw URLs not divided into separate table columns, you can count visitors to a particular page by extracting the 'PATH' or 'FILE' field, or analyze search terms by extracting the corresponding key from the 'QUERY' field.

REGEXP_ESCAPE(STRING source)
Purpose: The REGEXP_ESCAPE() function returns a string escaped for the special character in RE2 library so that the special characters are interpreted literally rather than as special characters. The following special characters are escaped by the function: |:-]]>

Return type: STRING

This example shows escaping one of special characters in RE2.

+------------------------------------------------------+ | regexp_escape('Hello.world') | +------------------------------------------------------+ | Hello\.world | +------------------------------------------------------+

This example shows escaping all the special characters in RE2.

q|r:s-t') | +------------------------------------------------------------+ | a\.b\\c\+d\*e\?f\[g\]h\$i\(j\)k\{l\}m\=n\!o\q\|r\:s\-t | +------------------------------------------------------------+ ]]>
REGEXP_EXTRACT(STRING subject, STRING pattern, INT index)
Purpose: Returns the specified () group from a string based on a regular expression pattern. Group 0 refers to the entire extracted string, while group 1, 2, and so on refers to the first, second, and so on (...) portion.

Return type: STRING

This example shows how group 0 matches the full pattern string, including the portion outside any () group:

[localhost:21000] > select regexp_extract('abcdef123ghi456jkl','.*?(\\d+)',0); +------------------------------------------------------+ | regexp_extract('abcdef123ghi456jkl', '.*?(\\d+)', 0) | +------------------------------------------------------+ | abcdef123ghi456 | +------------------------------------------------------+ Returned 1 row(s) in 0.11s

This example shows how group 1 matches just the contents inside the first () group in the pattern string:

[localhost:21000] > select regexp_extract('abcdef123ghi456jkl','.*?(\\d+)',1); +------------------------------------------------------+ | regexp_extract('abcdef123ghi456jkl', '.*?(\\d+)', 1) | +------------------------------------------------------+ | 456 | +------------------------------------------------------+ Returned 1 row(s) in 0.11s

Unlike in earlier Impala releases, the regular expression library used in Impala 2.0 and later supports the .*? idiom for non-greedy matches. This example shows how a pattern string starting with .*? matches the shortest possible portion of the source string, returning the rightmost set of lowercase letters. A pattern string both starting and ending with .*? finds two potential matches of equal length, and returns the first one found (the leftmost set of lowercase letters).

[localhost:21000] > select regexp_extract('AbcdBCdefGHI','.*?([[:lower:]]+)',1); +--------------------------------------------------------+ | regexp_extract('abcdbcdefghi', '.*?([[:lower:]]+)', 1) | +--------------------------------------------------------+ | def | +--------------------------------------------------------+ [localhost:21000] > select regexp_extract('AbcdBCdefGHI','.*?([[:lower:]]+).*?',1); +-----------------------------------------------------------+ | regexp_extract('abcdbcdefghi', '.*?([[:lower:]]+).*?', 1) | +-----------------------------------------------------------+ | bcd | +-----------------------------------------------------------+
REGEXP_LIKE(STRING source, STRING pattern[, STRING options])
Purpose: Returns true or false to indicate whether the source string contains anywhere inside it the regular expression given by the pattern. The optional third argument consists of letter flags that change how the match is performed, such as i for case-insensitive matching.

The flags that you can include in the optional third argument are:

  • c: Case-sensitive matching (the default).
  • i: Case-insensitive matching. If multiple instances of c and i are included in the third argument, the last such option takes precedence.
  • m: Multi-line matching. The ^ and $ operators match the start or end of any line within the source string, not the start and end of the entire string.
  • n: Newline matching. The . operator can match the newline character. A repetition operator such as .* can match a portion of the source string that spans multiple lines.

Return type: BOOLEAN

This example shows how regexp_like() can test for the existence of various kinds of regular expression patterns within a source string:

REGEXP_REPLACE(STRING initial, STRING pattern, STRING replacement)
Purpose: Returns the initial argument with the regular expression pattern replaced by the final argument string.

Return type: STRING

These examples show how you can replace parts of a string matching a pattern with replacement text, which can include backreferences to any () groups in the pattern string. The backreference numbers start at 1, and any \ characters must be escaped as \\.

Replace a character pattern with new text:

[localhost:21000] > select regexp_replace('aaabbbaaa','b+','xyz'); +------------------------------------------+ | regexp_replace('aaabbbaaa', 'b+', 'xyz') | +------------------------------------------+ | aaaxyzaaa | +------------------------------------------+ Returned 1 row(s) in 0.11s

Replace a character pattern with substitution text that includes the original matching text:

[localhost:21000] > select regexp_replace('aaabbbaaa','(b+)','<\\1>'); +----------------------------------------------+ | regexp_replace('aaabbbaaa', '(b+)', '<\\1>') | +----------------------------------------------+ | aaa<bbb>aaa | +----------------------------------------------+ Returned 1 row(s) in 0.11s

Remove all characters that are not digits:

[localhost:21000] > select regexp_replace('123-456-789','[^[:digit:]]',''); +---------------------------------------------------+ | regexp_replace('123-456-789', '[^[:digit:]]', '') | +---------------------------------------------------+ | 123456789 | +---------------------------------------------------+ Returned 1 row(s) in 0.12s
REPEAT(STRING str, INT n)
Purpose: Returns the argument string repeated a specified number of times.

Return type: STRING

REPLACE(STRING initial, STRING target, STRING replacement)
Purpose: Returns the initial argument with all occurrences of the target string replaced by the replacement string.

Return type: STRING

Because this function does not use any regular expression patterns, it is typically faster than regexp_replace() for simple string substitutions.

If any argument is NULL, the return value is NULL.

Matching is case-sensitive.

If the replacement string contains another instance of the target string, the expansion is only performed once, instead of applying again to the newly constructed string.

-- Replace one string with another. select replace('hello world','world','earth'); +------------------------------------------+ | replace('hello world', 'world', 'earth') | +------------------------------------------+ | hello earth | +------------------------------------------+ -- All occurrences of the target string are replaced. select replace('hello world','o','0'); +----------------------------------+ | replace('hello world', 'o', '0') | +----------------------------------+ | hell0 w0rld | +----------------------------------+ -- If no match is found, the original string is returned unchanged. select replace('hello world','xyz','abc'); +--------------------------------------+ | replace('hello world', 'xyz', 'abc') | +--------------------------------------+ | hello world | +--------------------------------------+

REVERSE(STRING a)
Purpose: Returns the argument string with characters in reversed order.

Return type: STRING

RIGHT(STRING a, INT num_chars)
See the STRRIGHT() function.
RPAD(STRING str, INT len, STRING pad)
Purpose: Returns a string of a specified length, based on the first argument string. If the specified string is too short, it is padded on the right with a repeating sequence of the characters from the pad string. If the specified string is too long, it is truncated on the right.

Return type: STRING

RTRIM(STRING a [, STRING chars_to_trim])
Purpose: Returns the argument string with all occurrences of characters specified by the second argument removed from the right side. Removes spaces if the second argument is not specified.

Return type: STRING

SPACE(INT n)
Purpose: Returns a concatenated string of the specified number of spaces. Shorthand for REPEAT(' ',n).

Return type: STRING

SPLIT_PART(STRING source, STRING delimiter, BIGINT n)
Purpose: Returns the nth field within a delimited string. The fields are numbered starting from 1. The delimiter can consist of multiple characters, not just a single character. All matching of the delimiter is done exactly, not using any regular expression patterns.

Return type: STRING

These examples show how to retrieve the nth field from a delimited string:

These examples show what happens for out-of-range field positions. Specifying a value less than 1 produces an error. Specifying a value greater than the number of fields returns a zero-length string (which is not the same as NULL).

These examples show how the delimiter can be a multi-character value:

STRLEFT(STRING a, INT num_chars)
Purpose: Returns the leftmost characters of the string. Shorthand for a call to SUBSTR() with 2 arguments.

Return type: STRING

STRRIGHT(STRING a, INT num_chars)
Purpose: Returns the rightmost characters of the string. Shorthand for a call to SUBSTR() with 2 arguments.

Return type: STRING

SUBSTR(STRING a, INT start [, INT len]), SUBSTRING(STRING a, INT start [, INT len])
Purpose: Returns the portion of the string starting at a specified point, optionally with a specified maximum length. The characters in the string are indexed starting at 1.

Return type: STRING

TRANSLATE(STRING input, STRING from, STRING to)
Purpose: Returns the input string with each character in the from argument replaced with the corresponding character in the to argument. The characters are matched in the order they appear in from and to.

For example: translate ('hello world','world','earth') returns 'hetta earth'.

Return type: STRING

Usage notes:

If from contains more characters than to, the from characters that are beyond the length of to are removed in the result.

For example:

translate('abcdedg', 'bcd', '1') returns 'a1eg'.

translate('Unit Number#2', '# ', '_') returns 'UnitNumber_2'.

If from is NULL, the function returns NULL.

If to contains more characters than from, the extra characters in to are ignored.

If from contains duplicate characters, the duplicate character is replaced with the first matching character in to.

For example: translate ('hello','ll','67') returns 'he66o'.

TRIM(STRING a)
Purpose: Returns the input string with both leading and trailing spaces removed. The same as passing the string through both LTRIM() and RTRIM().

Usage notes: Often used during data cleansing operations during the ETL cycle, if input values might still have surrounding spaces. For a more general-purpose function that can remove other leading and trailing characters besides spaces, see BTRIM().

Return type: STRING

UPPER(STRING a), UCASE(STRING a)
Purpose: Returns the argument string converted to all-uppercase.

Return type: STRING