String Functions - SQL Server to Aurora PostgreSQL Migration Playbook
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String Functions

Feature compatibility Amazon SCT / Amazon DMS automation level Amazon SCT action code index Key differences


                              Four star feature compatibility


                              Four star automation level

N/A

Syntax and option differences.

SQL Server Usage

String functions are typically scalar functions that perform an operation on string input and return a string or a numeric value.

Syntax and Examples

The following table includes the most commonly used string functions.

Function Purpose Example Result Comments

ASCII and UNICODE

Convert an ASCII or UNICODE character to its ASCII or UNICODE code.

SELECT ASCII ('A')

65

Returns a numeric integer value.

CHAR and NCHAR

Convert between ASCII or UNICODE code to a string character.

SELECT CHAR(65)

'A'

Numeric integer value as input.

CHARINDEX and PATINDEX

Find the starting position of one string expression or string pattern within another string expression.

SELECT CHARINDEX('ab','xabcdy')

2

Returns a numeric integer value.

CONCAT and CONCAT_WS

Combine multiple string input expressions into a single string with, or without, a separator character (WS).

SELECT CONCAT ('a','b'), CONCAT_WS(',','a','b')

'ab', 'a,b'

LEFT, RIGHT, and SUBSTRING

Return a partial string from another string expression based on position and length.

SELECT LEFT ('abs',2),SUBSTRING ('abcd',2,2)

'ab', 'bc'

LOWER and UPPER

Return a string with all characters in lower or upper case. Use for presentation or to handle case insensitive expressions.

SELECT LOWER('ABcd')

'abcd'

LTRIM, RTRIM, and TRIM

Remove leading and trailing spaces.

SELECT LTRIM ('abc d ')

'abc d '

STR

Convert a numeric value to a string.

SELECT STR(3.1415927,5,3)

3.142

Numeric expressions as input.

REVERSE

Return a string in reverse order.

SELECT REVERSE('abcd')

'dcba'

REPLICATE

Return a string that consists of zero or more concatenated copies of another string expression.

SELECT REPLICATE ('abc', 3)

'abcabcabc'

REPLACE

Replace all occurrences of a string expression with another.

SELECT REPLACE('abcd', 'bc', 'xy')

'axyd'

STRING_SPLIT

Parse a list of values with a separator and return a set of all individual elements.

SELECT * FROM STRING_SPLIT('1,2',',') AS X©

12

STRING_SPLIT is a table-valued function.

STRING_AGG

Return a string that consists of concatenated string values in row groups.

SELECT STRING_AGG(C, ',') FROM VALUES(1, 'a'), (1, 'b'), (2,'c') AS X (ID,C) GROUP BY I

1 'ab'

2 'c'

For more information, see String Functions (Transact-SQL) in the SQL Server documentation.

PostgreSQL Usage

Most of SQL Server string functions are supported in PostgreSQL, there are few which aren’t:

  • UNICODE returns the integer value of the first character as defined by the Unicode standard. If you will use UTF8 input, ASCII can be used to get the same results.

  • PATINDEX returns the starting position of the first occurrence of a pattern in a specified expression, or zeros if the pattern isn’t found, there is no equivalent function for that but you can create the same function with the same name so it will be fully compatible.

Some of the functions aren’t supported but they have an equivalent function in PostgreSQL that you can use to get the same functionality.

Some of the functions such as regular expressions don’t exist in SQL Server and may be useful for your application.

Syntax and Examples

The following table includes the most commonly used string functions.

PostgreSQL function Function definition

CONCAT

Concatenate the text representations of all the arguments: concat('a', 1) → a1. Also, can use the (||) operators: select 'a' ||' '|| 'b' → a b.

LOWER or UPPER

Returns char, with all letters lowercase or uppercase: lower ('MR. Smith') → mr. smith.

LPAD or RPAD

Returns expr1, left or right padded to length n characters with the sequence of characters in expr2: LPAD('Log-1',10,'@') → @@@@@Log-1.

REGEXP_REPLACE

Replace substrings matching a POSIX regular expression: regexp_replace('John', '[hn].', '1') → Jo1.

REGEXP_MATCHES or SUBSTRING

Return all captured substrings resulting from matching a POSIX regular expression against the string:

REGEXP_MATCHES ('http://www.aws.com/products', '(http://[[: alnum:]]+.*/)')

The result is {http://www.aws.com/}. You can use the following example

SUBSTRING ('http://www.aws.com/products', '(http://[[: alnum:]]+.*/)')

The result is http://www.aws.com/ .

REPLACE

Returns char with every occurrence of search string replaced with a replacement string: replace ('abcdef', 'abc', '123') → 123def.

LTRIM or RTRIM

Remove the longest string containing only characters from characters (a space by default) from the start of string: ltrim('zzzyaws', 'xyz') → aws.

SUBSTRING

Extract substring: substring ( 'John Smith', 6 ,1) → S.

TRIM

Remove the longest string containing only characters from characters (a space by default) from the start, end, or both ends: trim (both from 'yxJohnxx', 'xyz') → John.

ASCII

Returns the decimal representation in the database character set of the first character of char: ascii('a') → 97.

LENGTH

Return the length of char: length ('John S.') → 7.

To create the PATINDEX function, use the following code snippet. Note the 0 means that the expression doesn’t exist so the first position will be 1.

CREATE OR REPLACE FUNCTION "patindex"( "pattern" VARCHAR, "expression" VARCHAR )
RETURNS INT AS $BODY$
SELECT COALESCE(STRPOS($2,(
  SELECT(REGEXP_MATCHES($2,'(' ||
  REPLACE( REPLACE(TRIM( $1, '%' ), '%', '.*?' ), '_', '.' )
    || ')','i') )[ 1 ] LIMIT 1)),0);
$BODY$ LANGUAGE 'sql' IMMUTABLE;

SELECT patindex( 'Lo%', 'Long String' );

patindex
1

SELECT patindex( '%rin%', 'Long String' );
patindex
8

SELECT patindex( '%g_S%', 'Long String' );
patindex
4

Summary

SQL Server function Aurora PostgreSQL function

ASCII

ASCII

UNICODE

For UTF8 inputs, you can use only ASCII.

CHAR and NCHAR

CHR

CHARINDEX

POSITION

PATINDEX

See examples

CONCAT and CONCAT_WS

CONCAT and CONCAT_WS

LEFT, RIGHT, and SUBSTRING

LEFT, RIGHT, and SUBSTRING

LOWER and UPPER

LOWER and UPPER

LTRIM, RTRIM and TRIM

LTRIM, RTRIM and TRIM

STR

TO_CHAR

REVERSE

REVERSE

REPLICATE

LPAD

REPLACE

REPLACE

STRING_SPLIT

regexp_split_to_array or regexp_split_to_table

STRING_AGG

CONCAT_WS

For more information, see String Functions and Operators in the PostgreSQL documentation.