String Operators

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String Operators

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This page summarizes string operators for streaming SQL, including concatenation and string pattern comparison. These let you combine and compare strings.

Operator

Unary/Binary

Description

Notes

||

B

Concatenation

Concatenation also applies to binary types.

LIKE

B

String pattern comparison

<string> LIKE <like pattern> [ESCAPE <escape character>]

SIMILAR TO

B

String pattern comparison

<string> SIMILAR TO <similar to pattern> [ESCAPE <escape character>]

Concatenation

This operator is used to concatenate one or more strings:

Operation

Result

'SQL'||'stream'

SQLstream

'SQL'||''||'stream'

SQLstream

'SQL'||'stream'||' Incorporated'

SQLstream Incorporated

<col1>||<col2>||<col3>||<col4>

<col1><col2><col3><col4>

LIKE patterns

LIKE compares a string to a string pattern. In the pattern, the characters _ (underscore) and % (percent) have special meaning:

Character in pattern

Effect

_

Matches any single character

%

Matches any substring, including the empty string

<any other character>

Matches only the exact same character

If either operand is NULL, the result of the LIKE operation is UNKNOWN.

To explicitly match a special character in the character string, you must specify an escape character using the ESCAPE clause. The escape character must then precede the special character in the pattern. See examples below.

Operation

Result

'a' LIKE 'a'

TRUE

'a' LIKE 'A'

FALSE

'a' LIKE 'b'

FALSE

'ab' LIKE 'a_'

TRUE

'ab' LIKE 'a%'

TRUE

'ab' LIKE 'a\_' ESCAPE '\'

FALSE

'ab' LIKE 'a\%' ESCAPE '\'

FALSE

'a_' LIKE 'a\_' ESCAPE '\'

TRUE

'a%' LIKE 'a\%' ESCAPE '\'

TRUE

'a' LIKE 'a_'

FALSE

'a' LIKE 'a%'

TRUE

'abcd' LIKE 'a_'

FALSE

'abcd' LIKE 'a%'

TRUE

'' LIKE ''

TRUE

'1a' LIKE '_a'

TRUE

'123aXYZ' LIKE '%a%'

TRUE

'123aXYZ' LIKE '_%_a%_'

TRUE

SIMILAR TO patterns

SIMILAR TO compares a string to a pattern. It is much like the LIKE operator, but more powerful, as the patterns are regular expressions.

seq in the SIMILAR TO table below means any sequence of characters  explicitly specified, such as '13aq'. Non-alphanumeric characters intended for matching must be preceded by an escape character explicitly declared in the SIMILAR TO statement, such as '13aq\!' SIMILAR TO '13aq\!24br\!% ESCAPE '\'  (This statement is TRUE).

When a range is indicated, as when a dash is used in a pattern, the curent collating sequence is used. Typical ranges are 0-9 and a-z. This link provides a typical discussion of pattern-matching, including ranges.

When a line requires multiple comparisons, the innermost pattern that can be matched will be matched first, then the "next-innermost," etc.

Expressions and matching operations that are enclosed within parentheses are evaluated before surrounding operations are applied, again by innermost-first precedence.

SIMILAR TO Table

Delimiter

Character in pattern

Effect

Rule

parentheses (  )

 ( seq  )

Groups the seq (used for defining precedence of pattern expressions)

1

brackets [  ]

[ seq  ]

Matches any single character in the seq

2

caret or circumflex

[^seq ]

Matches any single character not in the seq

3

 

 [ seq ^ seq ]

Matches any single character in seq and not in seq

4

dash

<character1>-<character2>

Specifies a range of characters between character1 and character2

(using some known sequence like 1-9 or a-z)

5

bar

 [ seq seq ]

Matches either seq or seq

6

asterisk

seq*

Matches zero or more repetitions of seq

7

plus

seq+

Matches one or more repetitions of seq

8

braces

seq{<number>}

Matches exactly number repetitions of seq

9

 

seq{<low number>,<high number>}

Matches low number or more repetitions of seq , to a maximum of high number

10

question-mark

seq?

Matches zero or one instances of seq

11

underscore

_

Matches any single character

12

percent

%

Matches any substring, including the empty string

13

character

<any other character>

Matches only the exact same character

14

 NULL

 NULL

 If either operand is NULL, the result of the SIMILAR TO operation is UNKNOWN.

15

 Non-alphanumeric

Special characters

To explicitly match a special character in the character string,

that special character must be preceded by an escape character defined using

an ESCAPE clause specified at the end of the pattern.

16

See examples below.

Operation

Result

Rule

'a' SIMILAR TO 'a'

TRUE

14

'a' SIMILAR TO 'A'

FALSE

14

'a' SIMILAR TO 'b'

FALSE

14

'ab' SIMILAR TO 'a_'

TRUE

12

'ab' SIMILAR TO 'a%'

TRUE

13

'a' SIMILAR TO 'a_'

FALSE

12 & 14

'a' SIMILAR TO 'a%'

TRUE

13

'abcd' SIMILAR TO 'a_'

FALSE

12

'abcd' SIMILAR TO 'a%'

TRUE

13

'' SIMILAR TO ''

TRUE

14

'1a' SIMILAR TO '_a'

TRUE

12

'123aXYZ' SIMILAR TO ''

TRUE

14

'123aXYZ' SIMILAR TO '_%_a%_'

TRUE

13 & 12

'xy' SIMILAR TO '(xy)'

TRUE

1

'abd' SIMILAR TO '[ab][bcde]d'

TRUE

2

'bdd' SIMILAR TO '[ab][bcde]d'

TRUE

2

'abd' SIMILAR TO '[ab]d'

FALSE

2

'cd' SIMILAR TO '[a-e]d'

TRUE

2

'cd' SIMILAR TO '[a-e^c]d'

FALSE

4

'cd' SIMILAR TO '[^(a-e)]d'

INVALID

'yd' SIMILAR TO '[^(a-e)]d'

INVALID

'amy' SIMILAR TO 'amyfred'

TRUE

6

'fred' SIMILAR TO 'amyfred'

TRUE

6

'mike' SIMILAR TO 'amyfred'

FALSE

6

'acd' SIMILAR TO 'ab*c+d'

TRUE

7 & 8

'accccd' SIMILAR TO 'ab*c+d'

TRUE

7 & 8

'abd' SIMILAR TO 'ab*c+d'

FALSE

7 & 8

'aabc' SIMILAR TO 'ab*c+d'

FALSE

 

'abb' SIMILAR TO 'a(b{3})'

FALSE

9

'abbb' SIMILAR TO 'a(b{3})'

TRUE

9

'abbbbb' SIMILAR TO 'a(b{3})'

FALSE

9

'abbbbb' SIMILAR TO 'ab{3,6}'

TRUE

10

'abbbbbbbb' SIMILAR TO 'ab{3,6}'

FALSE

10

'' SIMILAR TO 'ab?'

FALSE

11

'' SIMILAR TO '(ab)?'

TRUE

11

'a' SIMILAR TO 'ab?'

TRUE

11

'a' SIMILAR TO '(ab)?'

FALSE

11

'a' SIMILAR TO 'a(b?)'

TRUE

11

'ab' SIMILAR TO 'ab?'

TRUE

11

'ab' SIMILAR TO 'a(b?)'

TRUE

11

'abb' SIMILAR TO 'ab?'

FALSE

11

'ab' SIMILAR TO 'a\_' ESCAPE '\'

FALSE

16

'ab' SIMILAR TO 'a\%' ESCAPE '\'

FALSE

16

'a_' SIMILAR TO 'a\_' ESCAPE '\'

TRUE

16

'a%' SIMILAR TO 'a\%' ESCAPE '\'

TRUE

16

'a(b{3})' SIMILAR TO 'a(b{3})'

FALSE

16

'a(b{3})' SIMILAR TO 'a\(b\{3\}\)' ESCAPE '\'

TRUE

16