String Manipulation (SQL)
Description
InterSystems SQL provides support for several types of string manipulation:
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Strings can be manipulated by length, character position, or substring value.
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Strings can be manipulated by a designated delimiter character or delimiter string.
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Strings can tested by pattern matching and word-aware searches.
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Specially encoded strings, called lists, contain embedded substring identifiers without using a delimiter character. The various $LIST functions operate on these encoded character strings, which are incompatible with standard character strings. The only exceptions are the $LISTGET function and the one-argument and two-argument forms of $LIST, which take an encoded character string as input, but output a single element value as a standard character string.
InterSystems SQL supports string functions, string condition expressions, and string operators.
ObjectScript string manipulation is case-sensitive. Letters in strings can be converted to uppercase, to lowercase, or retained as mixed case. String collation can be case-sensitive, or not case-sensitive; by default, SQL string collation is SQLUPPER which is not case-sensitive. InterSystems SQL provides numerous letter case and collation functions and operators.
When a string is specified for a numeric argument, most InterSystems SQL functions perform the following string-to-number conversions: a nonnumeric string is converted to the number 0; a numeric string is converted to a canonical number; and a mixed-numeric string is truncated at the first nonnumeric character and then converted to a canonical number.
String Concatenation
The following functions concatenate substrings into a string:
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CONCAT: concatenates two substrings, returns a single string.
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STRING: concatenates two or more substrings, returns a single string.
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XMLAGG: concatenates all of the values of a column, returns a single string. For further details, see Aggregate Functions.
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LIST: concatenates all of the values of a column, including a comma delimiter, returns a single string. For further details, see Aggregate Functions.
The concatenate operator (||) can also be used to concatenate two strings.
String Length
The following functions can be used to determine the length of a string:
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CHARACTER_LENGTH and CHAR_LENGTH: return the number of characters in a string, including trailing blanks. NULL returns NULL.
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LENGTH: returns the number of characters in a string, excluding trailing blanks. NULL returns NULL.
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$LENGTH: returns the number of characters in a string, including trailing blanks. NULL is returned as 0.
Truncation and Trimming
The following functions can be used to truncate or trim a string. Truncation limits the length of the string, deleting all characters beyond the specified length. Trimming deletes leading and/or trailing blank spaces from a string.
Substring Search
The following functions search for a substring within a string and return a string position:
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POSITION: searches by substring value, finds first match, returns position of beginning of substring.
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CHARINDEX: searches by substring value, finds first match, returns position of beginning of substring. Starting point can be specified.
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$FIND: searches by substring value, finds first match, returns position of end of substring. Starting point can be specified.
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INSTR: searches by substring value, finds first match, returns position of beginning of substring. Both starting point and substring occurrence can be specified.
The following functions search for a substring by position or delimiter within a string and return the substring:
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$EXTRACT: searches by string position, returns substring specified by start position, or start and end positions. Searches from beginning of string.
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SUBSTRING: searches by string position, returns substring specified by start position, or start and length. Searches from beginning of string.
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SUBSTR: searches by string position, returns substring specified by start position, or start and length. Searches from beginning or end of string.
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$PIECE: searches by delimiter character, returns first delimited substring. Starting point can be specified or defaults to beginning of string.
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$LENGTH: searches by delimiter character, returns the number of delimited substrings. Searches from beginning of string.
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$LIST: searches by substring count on a specially encoded list string. It locates a substring by substring count and returns the substring value. Searches from beginning of string.
The contains operator ([) can also be used to determine if a substring appears in a string.
The %STARTSWITH comparison operator matches the specified character(s) against the beginning of a string.
Substring Search–and–Replace
The following functions search for a substring within a string and replace it with another substring.
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REPLACE: searches by string value, replaces substring with new substring. Searches from beginning of string.
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STUFF: searches by string position and length, replaces substring with new substring. Searches from beginning of string.
Character-Type and Word-Aware Comparisons
The %PATTERN comparison operator matches a string to a specified pattern of character types.
You can perform a word-aware search of a string for specified words or phrases, including wildcard searching. For further details refer to Using InterSystems SQL Search.
