String Functions

**Table 1** String functions
SQL Function	Return Type	Description
string1 \|\| string2	STRING	Returns the concatenation of string1 and string2.
CHAR_LENGTH(string) CHARACTER_LENGTH(string)	INT	Returns the number of characters in the string.
UPPER(string)	STRING	Returns the string in uppercase.
LOWER(string)	STRING	Returns the string in lowercase.
POSITION(string1 IN string2)	INT	Returns the position (start from 1) of the first occurrence of string1 in string2; returns 0 if string1 cannot be found in string2.
TRIM([ BOTH \| LEADING \| TRAILING ] string1 FROM string2)	STRING	Returns a string that removes leading and/or trailing characters string2 from string1.
LTRIM(string)	STRING	Returns a string that removes the left whitespaces from the specified string. For example, LTRIM(' This is a test String.') returns "This is a test String.".
RTRIM(string)	STRING	Returns a string that removes the right whitespaces from the specified string. For example, RTRIM('This is a test String. ') returns "This is a test String.".
REPEAT(string, integer)	STRING	Returns a string that repeats the base string integer times. For example, REPEAT('This is a test String.', 2) returns "This is a test String.This is a test String.".
REGEXP_REPLACE(string1, string2, string3)	STRING	Returns a string from string1 with all the substrings that match a regular expression string2 consecutively being replaced with string3. For example, REGEXP_REPLACE('foobar', 'oo\|ar', '') returns "fb". REGEXP_REPLACE('ab\ab', '\\', 'e') returns "abeab".
OVERLAY(string1 PLACING string2 FROM integer1 [ FOR integer2 ])	STRING	Returns a string that replaces integer2 characters of STRING1 with STRING2 from position integer1. The default value of integer2 is the length of string2. For example, OVERLAY('This is an old string' PLACING ' new' FROM 10 FOR 5) returns "This is a new string".
SUBSTRING(string FROM integer1 [ FOR integer2 ])	STRING	Returns a substring of the specified string starting from position integer1 with length integer2 (to the end by default). If integer2 is not configured, the substring from integer1 to the end is returned by default.
REPLACE(string1, string2, string3)	STRING	Returns a new string which replaces all the occurrences of string2 with string3 (non-overlapping) from string1. For example, REPLACE('hello world', 'world', 'flink') returns "hello flink"; REPLACE('ababab', 'abab', 'z') returns "zab". REPLACE('ab\\ab', '\\', 'e') returns "abeab".
REGEXP_EXTRACT(string1, string2[, integer])	STRING	Returns a string from string1 which extracted with a specified regular expression string2 and a regex match group index integer. Returns NULL, if the parameter is NULL or the regular expression is invalid. For example, *REGEXP_EXTRACT('foothebar', 'foo(.?)(bar)', 2)" returns "bar"**.
INITCAP(string)	STRING	Returns a new form of STRING with the first character of each word converted to uppercase and the rest characters to lowercase.
CONCAT(string1, string2,...)	STRING	Returns a string that concatenates string1, string2, …. For example, CONCAT('AA', 'BB', 'CC') returns "AABBCC".
CONCAT_WS(string1, string2, string3,...)	STRING	Returns a string that concatenates string2, string3, … with a separator string1. The separator is added between the strings to be concatenated. Returns NULL if string1 is NULL. If other arguments are NULL, this function automatically skips NULL arguments. For example, CONCAT_WS('~', 'AA', NULL, 'BB', '', 'CC') returns "AA~BB~~CC".
LPAD(string1, integer, string2)	STRING	Returns a new string from string1 left-padded with string2 to a length of integer characters. If any argument is NULL, NULL is returned. If integer is negative, NULL is returned. If the length of string1 is shorter than integer, returns string1 shortened to integer characters. For example, LPAD(Symbol,4,Symbol) returns "Symbol hi". LPAD('hi',1,'??') returns "h".
RPAD(string1, integer, string2)	STRING	Returns a new string from string1 right-padded with string2 to a length of integer characters. If any argument is NULL, NULL is returned. If integer is negative, NULL is returned. If the length of string1 is shorter than integer, returns string1 shortened to integer characters. For example, RPAD('hi',4,'??') returns "hi??". RPAD('hi',1,'??') returns "h".
FROM_BASE64(string)	STRING	Returns the base64-decoded result from string. Returns NULL if string is NULL. For example, FROM_BASE64('aGVsbG8gd29ybGQ=') returns "hello world".
TO_BASE64(string)	STRING	Returns the base64-encoded result from string; f string is NULL. Returns NULL if string is NULL. For example, TO_BASE64(hello world) returns "aGVsbG8gd29ybGQ=".
ASCII(string)	INT	Returns the numeric value of the first character of string. Returns NULL if string is NULL. For example, ascii('abc') returns 97. ascii(CAST(NULL AS VARCHAR)) returns NULL.
CHR(integer)	STRING	Returns the ASCII character having the binary equivalent to integer. If integer is larger than 255, we will get the modulus of integer divided by 255 first, and returns CHR of the modulus. Returns NULL if integer is NULL. chr(97) returns a. chr(353) Return a.
DECODE(binary, string)	STRING	Decodes the first argument into a String using the provided character set (one of 'US-ASCII', 'ISO-8859-1', 'UTF-8', 'UTF-16BE', 'UTF-16LE', 'UTF-16'). If either argument is NULL, the result will also be NULL.
ENCODE(strinh1, string2)	STRING	Encodes the string1 into a BINARY using the provided string2 character set (one of 'US-ASCII', 'ISO-8859-1', 'UTF-8', 'UTF-16BE', 'UTF-16LE', 'UTF-16'). If either argument is NULL, the result will also be NULL.
INSTR(string1, string2)	INT	Returns the position of the first occurrence of string2 in string1. Returns NULL if any argument is NULL.
LEFT(string, integer)	STRING	Returns the leftmost integer characters from the string. Returns EMPTY String if integer is negative. Returns NULL if any argument is NULL.
RIGHT(string, integer)	STRING	Returns the rightmost integer characters from the string. Returns EMPTY String if integer is negative. Returns NULL if any argument is NULL.
LOCATE(string1, string2[, integer])	INT	Returns the position of the first occurrence of string1 in string2 after position integer. Returns 0 if not found. The value of integer defaults to 0. Returns NULL if any argument is NULL.
PARSE_URL(string1, string2[, string3])	STRING	Returns the specified part from the URL. Valid values for string2 include 'HOST', 'PATH', 'QUERY', 'REF', 'PROTOCOL', 'AUTHORITY', 'FILE', and 'USERINFO'. Returns NULL if any argument is NULL. If string2 is QUERY, the key in QUERY can be specified as string3. Example: The parse_url('http://facebook.com/path1/p.php?k1=v1&k2=v2#Ref1', 'HOST') returns 'facebook.com'. parse_url('http://facebook.com/path1/p.php?k1=v1&k2=v2#Ref1', 'QUERY', 'k1') returns 'v1'.
REGEXP(string1, string2)	BOOLEAN	Returns TRUE if any (possibly empty) substring of string1 matches the regular expression string2, otherwise FALSE. If the information is found, TRUE is returned. string1 indicates the specified string, and string2 indicates the regular expression. Returns NULL if any argument is NULL.
REVERSE(string)	STRING	Returns the reversed string. Returns NULL if string is NULL.
SPLIT_INDEX(string1, string2, integer1)	STRING	Splits string1 by the delimiter string2, returns the integer1-th (zero-based) string of the split strings. Returns NULL if integer is negative. Returns NULL if any argument is NULL.
STR_TO_MAP(string1[, string2, string3]])	MAP	Returns a map after splitting the string1 into key/value pairs using delimiters. The default value of string2 is ','. The default value of string3 is '='.
SUBSTR(string[, integer1[, integer2]])	STRING	Returns a substring of string starting from position integer1 with length integer2. If integer2 is not specified, the string is truncated to the end.
JSON_VAL(STRING json_string, STRING json_path)	STRING	Returns the value of the specified json_path from the json_string. For details about how to use the functions, see JSON_VAL Function. NOTE: The following rules are listed in descending order of priority. The two arguments json_string and json_path cannot be NULL. The value of json_string must be a valid JSON string. Otherwise, the function returns NULL. If json_string is an empty string, the function returns an empty string. If json_path is an empty string or the path does not exist, the function returns NULL.

JSON_VAL Function

Syntax

STRING JSON_VAL(STRING json_string, STRING json_path)

**Table 2** Parameter description
Parameter	Type	Description
json_string	STRING	JSON object to be parsed
json_path	STRING	Path expression for parsing the JSON string For the supported expressions, see Table 3.

**Table 3** Expressions supported
Expression	Description
$	Root node in the path
[]	Access array elements
*	Array wildcard
.	Access child elements

Example

Test input data.

Test the data source kafka. The message content is as follows:

"{name:James,age:24,gender:male,grade:{math:95,science:[80,85],english:100}}"
"{name:James,age:24,gender:male,grade:{math:95,science:[80,85],english:100}]"

Use JSON_VAL in SQL statements.

create table kafkaSource(
  message STRING
)
with (
  'connector.type' = 'kafka',
  'connector.version' = '0.11',
  'connector.topic' = 'topic-swq',
  'connector.properties.bootstrap.servers' = 'xxx.xxx.xxx.xxx:9092,yyy.yyy.yyy:9092,zzz.zzz.zzz.zzz:9092',
  'connector.startup-mode' = 'earliest-offset',
  'format.field-delimiter' = '|',
  'format.type' = 'csv'
);

create table kafkaSink(
  message1 STRING,
  message2 STRING,
  message3 STRING,
  message4 STRING,
  message5 STRING,
  message6 STRING
)
with (
  'connector.type' = 'kafka',
  'connector.version' = '0.11',
  'connector.topic' = 'topic-swq-out',
  'connector.properties.bootstrap.servers' = 'xxx.xxx.xxx.xxx:9092,yyy.yyy.yyy:9092,zzz.zzz.zzz.zzz:9092',
  'format.type' = 'json'
);

INSERT INTO kafkaSink
SELECT 
JSON_VAL(message,""),
JSON_VAL(message,"$.name"),
JSON_VAL(message,"$.grade.science"),
JSON_VAL(message,"$.grade.science[*]"),
JSON_VAL(message,"$.grade.science[1]"),
JSON_VAL(message,"$.grade.dddd")
FROM kafkaSource;

View output.

{"message1":null,"message2":"swq","message3":"[80,85]","message4":"[80,85]","message5":"85","message6":null}
{"message1":null,"message2":null,"message3":null,"message4":null,"message5":null,"message6":null}

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