Text functions

This page describes the available functions to assist with performing text manipulation such as concatenation, case conversion, and string length calculation.

concat

concat(str, ...) - concatenates a string from one or more input values.

Example

SELECT firstName, lastName, concat(firstName, ' ', lastName) FROM names;

firstName	lastName	concat
Tim	Thompson	Tim Thompson
Anna	Thompson	Anna Thompson
Anna	Mason	Anna Mason
Tom	Johnson	Tom Johnson
Tim	Smith	Tim Smith

tip

concat() can be used to generate line protocol. See an example below.

Generating line protocol
SELECT
concat(
    'trades,instrument=', rnd_str(2,2,0),
    ',side=', rnd_str('B', 'S'),
    ' price=', abs(cast(rnd_double(0)*100000 AS INT)),
    ',quantity=', abs(cast(rnd_double(0)*10000 AS INT)),
    ' ',
    1571270400000 + (x-1) * 100
)
FROM long_sequence(5) x;

trades,instrument=CR,side=B price=70867,quantity=9192 1571270400000
trades,instrument=LN,side=S price=37950,quantity=1439 1571270400100
trades,instrument=ZJ,side=S price=82829,quantity=8871 1571270400200
trades,instrument=EW,side=S price=10427,quantity=1945 1571270400300
trades,instrument=MI,side=B price=99348,quantity=8450 1571270400400

length

length(string) - reads length of string value type (result is int)

length(symbol) - reads length of symbol value type (result is int)

length(blob) - reads length of binary value type (result is long)

a string
a symbol
a binary blob

Example

SELECT name a, length(name) b FROM names limit 4

a	b
AARON	5
AMELIE	6
TOM	3
null	-1

left

left(string, count) - extracts a substring of the given length from a string (starting from left).

Arguments:

string is a string to extract from.
count is an integer specifying the count of characters to be extracted into a substring.

Return value:

Returns a string with the extracted characters.

Examples:

Example

SELECT name, left('Thompson', 3) l FROM names LIMIT 3

name	l
AARON	AAR
AMELIE	AME
TOM	TOM

right

right(string, count) - extracts a substring of the given length from a string (starting from right).

Arguments:

string is a string to extract from.
count is an integer specifying the count of characters to be extracted into a substring.

Return value:

Returns a string with the extracted characters.

Examples:

Example

SELECT name, right('Thompson', 2) r FROM names LIMIT 3

name	l
AARON	ON
AMELIE	IE
TOM	OM

replace

replace replaces all occurrences of a substring within a string with another substring.

Arguments:

replace(string, from_string, to_string)
- string is the original string where replacements will be made.
- from_string is the substring that will be searched for in the original string.
- to_string is the substring that will replace occurrences of from_string.

Return value:

Returns a new string that is derived from the original string by replacing every occurrence of from_string with to_string.

Examples:

SELECT replace('Hello World', 'World', 'QuestDB');

replace
Hello QuestDB

lpad

Arguments:

lpad(string, length, fill)
- string is the input string that you want to pad.
- length is the length of the resulting string after padding. If this is less than the length of the original string, the original string is truncated to the specified length.
- fill is the string to use for padding. If this is not specified, spaces are used.

Return value:

Returns a string that is padded on the left with the specified fill string to the specified length.

Example:

Using lpad function

SELECT lpad('QuestDB', 10, '0') AS padded_string;

lpad
000QuestDB

ltrim

Arguments:

ltrim(string)
- string is the input string from which you want to remove leading whitespace.

Return value:

Returns a string with leading whitespace removed.

Example:

Using ltrim function

SELECT ltrim('   QuestDB   ') AS trimmed_string;

trim
QuestDB

rtrim

rtrim extracts white space from the right of a string value.

Arguments:

rtrim(string)

Return value:

Returns a new string derived from the original string, minus all trailing occurrences of white space.

Examples:

SELECT rtrim('Hello QuestDB   ');

rtrim
Hello QuestDB

trim

Arguments:

trim(string)
- string is the input string from which you want to remove leading and trailing whitespace.

Return value:

Returns a string with leading and trailing whitespace removed.

Example:

Using trim function

SELECT trim('   QuestDB   ') AS trimmed_string;

trim
QuestDB

split_part

Arguments:

split_part(string, delimiter, part)
- string is the original string that will be split.
- delimiter is the character or characters that will be used to split the string.
- part is an integer that specifies which part to return, starting from 1.

Return value:

Returns the part at the specified position from the string that has been split by the delimiter.

Examples:

SELECT split_part('Hello,QuestDB,SQL', ',', 2);

split_part
QuestDB

starts_with

Arguments:

starts_with(string, substring)
- string is the original string that will be checked.
- substring is the substring that will be checked if it's at the start of the original string.

Return value:

Returns true if the original string starts with the specified substring, false otherwise.

Examples:

SELECT starts_with('Hello QuestDB', 'Hello');

starts_with
true

string_agg

Arguments:

string_agg(expression, delimiter)
- expression is the string that will be aggregated.
- delimiter is the string that will be inserted between the values in the result string.

Return value:

Returns a string that is the result of concatenating all the string values in a group, separated by the specified delimiter.

Examples:

SELECT string_agg(make, ',') as makes
FROM sensors;

makes
Honeywell,Honeywell,United Automation,United Automation,...

It's common to append a LIMIT so that, such as in this case, the values repeat:

SELECT string_agg(make, ',') as makes
FROM (
  SELECT make
  FROM sensors
  LIMIT 10
) sub;

This will return 10 concatenated strings.

strpos / position

strpos(string, substring) or position(string, substring) - searches for the first substring occurrence in a string, and returns the index position of the starting character. If the substring is not found, this function returns 0. The performed search is case-sensitive.

Arguments:

string is a string to search in.
substring is a string to search for.

Return value:

Returns an integer for the substring position. Positions start from 1.

Examples:

Example
SELECT name, strpos(name, 'Thompson') idx
FROM full_names
LIMIT 4;

-- This is equal to:
SELECT name, position(name, 'Thompson') idx
FROM full_names
LIMIT 4;

name	idx
Tim Thompson	5
Anna Thompson	6
Anna Mason	0
Tom Johnson	0

Assuming we have a table example_table with a single string type column col:

col
apple,pear
cat,dog
...

As a more advanced example, we can use strpos() or position() to split the string values of col, in this case splitting at the comma character, , . By using left()/right() functions, we can choose the string values at the left and right of the comma:

Splitting string into two separate columns
SELECT col,
       left(col, strpos(col, ',') - 1) as col1,
       right(col, length(col) - strpos(col, ',')) as col2
FROM example_table;

-- This is equal to:

SELECT col,
       left(col, position(col, ',') - 1) as col1,
       right(col, length(col) - position(col, ',')) as col2
FROM example_table;

col	col1	col2
apple,pear	apple	pear
cat,dog	cat	dog

substring

substring(string, start, length) - extracts a substring from the given string.

Arguments:

string is a string to extract from.
start is an integer specifying the position of the first character to be extracted. Positions start from 1.
length is an integer specifying the count of characters to be extracted. Should be non-negative.

Return value:

Returns a string with the extracted characters. If any part the arguments is null, the function returns null.

Examples:

Example

SELECT id, substring(id, 1, 2) country FROM orders LIMIT 3

id	country
UK2022072619373	UK
UK2022072703162	UK
US2022072676246	US

If the start argument is negative, the output depends on the value of start+length:

If start+length is greater than 1, the substring stops at position start+length - 1.
If start+length is zero, the output is empty string.
If start+length is less than zero, the output is null.

Example

SELECT substring('Lorem ipsum dolor sit amet', -5, 9)

substring
Lor

to_lowercase / lower

to_lowercase(string) or lower(string) - converts all upper case string characters to lowercase

Arguments:

string is the input strong to be converted.

Return value:

Return value type is string.

Examples:

SELECT lower('questDB');
-- This is equal to:
SELECT to_lowercase('questDB');

to_lowercase
questdb

to_uppercase / upper

to_uppercase(string) or upper(string) - converts all lower case string characters to uppercase

Arguments:

string is the input strong to be converted.

Return value:

Return value type is string.

Examples:

SELECT upper('questDB');
-- This is equal to:
SELECT to_uppercase('questDB');

to_uppercase
QUESTDB

concat​

length​

left​

right​

replace​

lpad​

ltrim​

rtrim​

trim​

split_part​

starts_with​

string_agg​

strpos / position​

substring​

to_lowercase / lower​

to_uppercase / upper​

concat

length

left

right

replace

lpad

ltrim

rtrim

trim

split_part

starts_with

string_agg

strpos / position

substring

to_lowercase / lower

to_uppercase / upper