8.3String and Binary Functions

8.3.1ASCII_CHAR()

Character from ASCII code

Result typeCHAR(1) CHARACTER SET NONE

Syntax

  |ASCII_CHAR (code)

Table 8.30ASCII_CHAR Function Parameter
ParameterDescription

code

An integer within the range from 0 to 255

Returns the ASCII character corresponding to the number passed in the argument.

Important
  • If you are used to the behaviour of the ASCII_CHAR UDF, which returns an empty string if the argument is 0, please notice that the internal function returns a character with ASCII code 0 (character NUL) here.

See alsoSection 8.3.2, “ASCII_VAL(), Section 8.3.24, “UNICODE_CHAR()

8.3.2ASCII_VAL()

ASCII code from string

Result typeSMALLINT

Syntax

  |ASCII_VAL (ch)

Table 8.31ASCII_VAL Function Parameter
ParameterDescription

ch

A string of the [VAR]CHAR data type or a text BLOB with the maximum size of 32,767 bytes

Returns the ASCII code of the character passed in.

  • If the argument is a string with more than one character, the ASCII code of the first character is returned.

  • If the argument is an empty string, 0 is returned.

  • If the argument is NULL, NULL is returned.

  • If the first character of the argument string is multi-byte, an error is raised.

See alsoSection 8.3.1, “ASCII_CHAR(), Section 8.3.25, “UNICODE_VAL()

8.3.3BASE64_DECODE()

Decodes a base64 string to binary

Result typeVARBINARY or BLOB

Syntax

  |BASE64_DECODE (base64_data)

Table 8.32BASE64_DECODE Function Parameter
ParameterDescription

base64_data

Base64 encoded data, padded with = to multiples of 4

BASE64_DECODE decodes a string with base64-encoded data, and returns the decoded value as VARBINARY or BLOB as appropriate for the input. If the length of the type of base64_data is not a multiple of 4, an error is raised at prepare time. If the length of the value of base64_data is not a multiple of 4, an error is raised at execution time.

When the input is not BLOB, the length of the resulting type is calculated as type_length * 3 / 4, where type_length is the maximum length in characters of the input type.

8.3.3.1Example of BASE64_DECODE

  |select cast(base64_decode('VGVzdCBiYXNlNjQ=') as varchar(12))
  |from rdb$database;
  | 
  |CAST
  |============
  |Test base64

See alsoSection 8.3.4, “BASE64_ENCODE(), Section 8.3.10, “HEX_DECODE()

8.3.4BASE64_ENCODE()

Encodes a (binary) value to a base64 string

Result typeVARCHAR CHARACTER SET ASCII or BLOB SUB_TYPE TEXT CHARACTER SET ASCII

Syntax

  |BASE64_ENCODE (binary_data)

Table 8.33BASE64_ENCODE Function Parameter
ParameterDescription

binary_data

Binary data (or otherwise convertible to binary) to encode

BASE64_ENCODE encodes binary_data with base64, and returns the encoded value as a VARCHAR CHARACTER SET ASCII or BLOB SUB_TYPE TEXT CHARACTER SET ASCII as appropriate for the input. The returned value is padded with = so its length is a multiple of 4.

When the input is not BLOB, the length of the resulting type is calculated as type_length * 4 / 3 rounded up to a multiple of four, where type_length is the maximum length in bytes of the input type. If this length exceeds the maximum length of VARCHAR, the function returns a BLOB.

8.3.4.1Example of BASE64_ENCODE

  |select base64_encode('Test base64')
  |from rdb$database;
  | 
  |BASE64_ENCODE
  |================
  |VGVzdCBiYXNlNjQ=

See alsoSection 8.3.3, “BASE64_DECODE(), Section 8.3.11, “HEX_ENCODE()

8.3.5BIT_LENGTH()

String or binary length in bits

Result typeINTEGER, or BIGINT for BLOB

Syntax

  |BIT_LENGTH (string)

Table 8.34BIT_LENGTH Function Parameter
ParameterDescription

string

An expression of a string type

Gives the length in bits of the input string. For multibyte character sets, this may be less than the number of characters times 8 times the formal number of bytes per character as found in RDB$CHARACTER_SETS.

With arguments of type CHAR, this function takes the entire formal string length (i.e. the declared length of a field or variable) into account. If you want to obtain the logical bit length, not counting the trailing spaces, right-TRIM the argument before passing it to BIT_LENGTH.

8.3.5.1BIT_LENGTH Examples

   |select bit_length('Hello!') from rdb$database
   |-- returns 48
   | 
   |select bit_length(_iso8859_1 'Grüß di!') from rdb$database
   |-- returns 64: ü and ß take up one byte each in ISO8859_1
   | 
   |select bit_length
   |  (cast (_iso8859_1 'Grüß di!' as varchar(24) character set utf8))
   |from rdb$database
   |-- returns 80: ü and ß take up two bytes each in UTF8
   | 
   |select bit_length
   |  (cast (_iso8859_1 'Grüß di!' as char(24) character set utf8))
   |from rdb$database
   |-- returns 208: all 24 CHAR positions count, and two of them are 16-bit

See alsoSection 8.3.15, “OCTET_LENGTH(), Section 8.3.7, “CHAR_LENGTH(), CHARACTER_LENGTH()

8.3.6BLOB_APPEND()

Efficient concatenation of blobs

Result typeBLOB

Syntax

  |BLOB_APPEND(expr1, expr2 [, exprN ... ])

Table 8.35BLOB_APPEND Function Parameters
ParameterDescription

exprN

An expression of a type convertible to BLOB

The BLOB_APPEND function concatenates blobs without creating intermediate BLOBs, avoiding excessive memory consumption and growth of the database file. The BLOB_APPEND function takes two or more arguments and adds them to a BLOB which remains open for further modification by a subsequent BLOB_APPEND call.

The resulting BLOB is left open for writing instead of being closed when the function returns. In other words, the BLOB can be appended as many times as required. The engine marks the BLOB returned by BLOB_APPEND with an internal flag, BLB_close_on_read, and closes it automatically when needed.

The first argument determines the behaviour of the function:

  1. NULL: new, empty BLOB SUB_TYPE TEXT is created, using the connection character set as the character set

  2. permanent BLOB (from a table) or temporary BLOB which was already closed: new BLOB is created with the same subtype and, if subtype is TEXT the same character set, populated with the content of the original BLOB.

  3. temporary unclosed BLOB with the BLB_close_on_read flag (e.g. created by another call to BLOB_APPEND): used as-is, remaining arguments are appended to this BLOB

  4. other data types: a new BLOB SUB_TYPE TEXT is created, populated with the original argument converted to string. If the original value is a character type, its character set is used (for string literals, the connection character set), otherwise the connection character set.

Other arguments can be of any type. The following behavior is defined for them:

  1. NULLs are ignored (behaves as empty string)

  2. BLOBs, if necessary, are transliterated to the character set of the first argument and their contents are appended to the result

  3. other data types are converted to strings (as usual) and appended to the result

The BLOB_APPEND function returns a temporary unclosed BLOB with the BLB_close_on_read flag. If the first argument is such a temporary unclosed BLOB (e.g. created by a previous call to BLOB_APPEND), it will be used as-is, otherwise a new BLOB is created. Thus, a series of operations like blob = BLOB_APPEND (blob, …​) will result in the creation of at most one BLOB (unless you try to append a BLOB to itself). This blob will be automatically closed by the engine when the client reads it, assigns it to a table, or uses it in other expressions that require reading the content.

🛑
Important caveats for BLOB_APPEND
  1. The NULL behaviour of BLOB_APPEND is different from normal concatenation (using ||). Occurrence of NULL will behave as if an empty string was used. In other words, NULL is effectively ignored.

    In normal concatenation, concatenating with NULL results in NULL.

  2. Testing a blob for NULL using the IS [NOT] NULL operator does not read it and therefore a temporary blob with the BLB_close_on_read flag will not be closed after such a test.

Tip

Use LIST or BLOB_APPEND functions to concatenate blobs. This reduces memory consumption and disk I/O, and also prevents database growth due to the creation of many temporary blobs when using the concatenation operator.

8.3.6.1BLOB_APPEND Examples

   |execute block
   |returns (b blob sub_type text)
   |as
   |begin
   |  -- creates a new temporary not closed BLOB
   |  -- and writes the string from the 2nd argument into it
   |  b = blob_append(null, 'Hello ');
   | 
   |  -- adds two strings to the temporary BLOB without closing it
   |  b = blob_append(b, 'World', '!');
   | 
   |  -- comparing a BLOB with a string will close it, because the BLOB needs to be read
   |  if (b = 'Hello World!') then
   |  begin
   |  -- ...
   |  end
   | 
   |  -- creates a temporary closed BLOB by adding a string to it
   |  b = b || 'Close';
   | 
   |  suspend;
   |end

See alsoConcatenation Operator, LIST(), RDB$BLOB_UTIL

8.3.7CHAR_LENGTH(), CHARACTER_LENGTH()

String length in characters

Result typeINTEGER, or BIGINT for BLOB

Syntax

  |  CHAR_LENGTH (string)
  || CHARACTER_LENGTH (string)

Table 8.36CHAR[ACTER]_LENGTH Function Parameter
ParameterDescription

string

An expression of a string type

Gives the length in characters of the input string.

With arguments of type CHAR, this function returns the formal string length (i.e. the declared length of a field or variable). If you want to obtain the logical length, not counting the trailing spaces, right-TRIM the argument before passing it to CHAR[ACTER]_LENGTH.

This function fully supports text BLOBs of any length and character set.

8.3.7.1CHAR_LENGTH Examples

   |select char_length('Hello!') from rdb$database
   |-- returns 6
   | 
   |select char_length(_iso8859_1 'Grüß di!') from rdb$database
   |-- returns 8
   | 
   |select char_length
   |  (cast (_iso8859_1 'Grüß di!' as varchar(24) character set utf8))
   |from rdb$database
   |-- returns 8; the fact that ü and ß take up two bytes each is irrelevant
   | 
   |select char_length
   |  (cast (_iso8859_1 'Grüß di!' as char(24) character set utf8))
   |from rdb$database
   |-- returns 24: all 24 CHAR positions count

See alsoSection 8.3.5, “BIT_LENGTH(), Section 8.3.15, “OCTET_LENGTH()

8.3.8CRYPT_HASH()

Cryptographic hash

Result typeVARBINARY

Syntax

  |CRYPT_HASH (value USING <hash>)
  | 
  |<hash> ::= MD5 | SHA1 | SHA256 | SHA512

Table 8.37CRYPT_HASH Function Parameter
ParameterDescription

value

Expression of value of any type; non-string or non-binary types are converted to string

hash

Cryptographic hash algorithm to apply

CRYPT_HASH returns a cryptographic hash calculated from the input argument using the specified algorithm. If the input argument is not a string or binary type, it is converted to string before hashing.

This function returns a VARBINARY with the length depending on the specified algorithm.

Note
  • The MD5 and SHA1 algorithms are not recommended for security purposes due to known attacks to generate hash collisions. These two algorithms are provided for backward-compatibility only.

  • When hashing string or binary values, take into account the effects of trailing blanks (spaces or NULs). The value 'ab' in a CHAR(5) (3 trailing spaces) has a different hash than if it is stored in a VARCHAR(5) (no trailing spaces) or CHAR(6) (4 trailing spaces).

    To avoid this, make sure you always use a variable length data type, or the same fixed length data type, or normalize values before hashing, for example using TRIM(TRAILING FROM value).

8.3.8.1Examples of CRYPT_HASH

Hashing x with the SHA512 algorithm

  |select crypt_hash(x using sha512) from y;

See alsoSection 8.3.9, “HASH()

8.3.9HASH()

Non-cryptographic hash

Result typeINTEGER, BIGINT

Syntax

  |HASH (value [USING <hash>])
  | 
  |<hash> ::= CRC32

Table 8.38HASH Function Parameter
ParameterDescription

value

Expression of value of any type; non-string or non-binary types are converted to string

hash

Non-cryptographic hash algorithm to apply

HASH returns a hash value for the input argument. If the input argument is not a string or binary type, it is converted to string before hashing.

The optional USING clause specifies the non-cryptographic hash algorithm to apply. When the USING clause is absent, the legacy PJW algorithm is applied; this is identical to its behaviour in previous Firebird versions.

This function fully supports text BLOBs of any length and character set.

Supported algorithms
not specified

When no algorithm is specified, Firebird applies the 64-bit variant of the non-cryptographic PJW hash function (also known as ELF64). This is a fast algorithm for general purposes (hash tables, etc.), but its collision quality is suboptimal. Other hash functions — specified explicitly in the USING clause, or cryptographic hashes through Section 8.3.8, “CRYPT_HASH() — should be used for more reliable hashing.

The HASH function returns BIGINT for this algorithm

CRC32

With CRC32, Firebird applies the CRC32 algorithm using the polynomial 0x04C11DB7.

The HASH function returns INTEGER for this algorithm.

8.3.9.1Examples of HASH

  1. Hashing x with the CRC32 algorithm

      |select hash(x using crc32) from y;
    
  2. Hashing x with the legacy PJW algorithm

      |select hash(x) from y;
    

See alsoSection 8.3.8, “CRYPT_HASH()

8.3.10HEX_DECODE()

Decode a hexadecimal string to binary

Result typeVARBINARY or BLOB

Syntax

  |HEX_DECODE (hex_data)

Table 8.39HEX_DECODE Function Parameter
ParameterDescription

hex_data

Hex encoded data

HEX_DECODE decodes a string with hex-encoded data, and returns the decoded value as VARBINARY or BLOB as appropriate for the input. If the length of the type of hex_data is not a multiple of 2, an error is raised at prepare time. If the length of the value of hex_data is not a multiple of 2, an error is raised at execution time.

When the input is not BLOB, the length of the resulting type is calculated as type_length / 2, where type_length is the maximum length in characters of the input type.

8.3.10.1Example of HEX_DECODE

  |select cast(hex_decode('48657861646563696D616C') as varchar(12))
  |from rdb$database;
  | 
  |CAST
  |============
  |Hexadecimal

See alsoSection 8.3.11, “HEX_ENCODE(), Section 8.3.3, “BASE64_DECODE()

8.3.11HEX_ENCODE()

Encodes a (binary) value to a hexadecimal string

Result typeVARCHAR CHARACTER SET ASCII or BLOB SUB_TYPE TEXT CHARACTER SET ASCII

Syntax

  |HEX_ENCODE (binary_data)

Table 8.40HEX_ENCODE Function Parameter
ParameterDescription

binary_data

Binary data (or otherwise convertible to binary) to encode

HEX_ENCODE encodes binary_data with hex, and returns the encoded value as a VARCHAR CHARACTER SET ASCII or BLOB SUB_TYPE TEXT CHARACTER SET ASCII as appropriate for the input.

When the input is not BLOB, the length of the resulting type is calculated as type_length * 2, where type_length is the maximum length in bytes of the input type. If this length exceeds the maximum length of VARCHAR, the function returns a BLOB.

8.3.11.1Example of HEX_ENCODE

  |select hex_encode('Hexadecimal')
  |from rdb$database;
  | 
  |HEX_ENCODE
  |======================
  |48657861646563696D616C

See alsoSection 8.3.10, “HEX_DECODE(), Section 8.3.4, “BASE64_ENCODE()

8.3.12LEFT()

Extracts the leftmost part of a string

Result typeVARCHAR or BLOB

Syntax

  |LEFT (string, length)

Table 8.41LEFT Function Parameters
ParameterDescription

string

An expression of a string type

length

Integer expression. The number of characters to return

  • This function fully supports text BLOBs of any length, including those with a multi-byte character set.

  • If string is a BLOB, the result is a BLOB. Otherwise, the result is a VARCHAR(n) with n the length of the input string.

  • If the length argument exceeds the string length, the input string is returned unchanged.

  • If the length argument is not a whole number, bankers' rounding (round-to-even) is applied, i.e. 0.5 becomes 0, 1.5 becomes 2, 2.5 becomes 2, 3.5 becomes 4, etc.

See alsoSection 8.3.20, “RIGHT()

8.3.13LOWER()

Converts a string to lowercase

Result type(VAR)CHAR, (VAR)BINARY or BLOB

Syntax

  |LOWER (string)

Table 8.42LOWER Function ParameterS
ParameterDescription

string

An expression of a string type

Returns the lowercase equivalent of the input string. The exact result depends on the character set. With ASCII or NONE for instance, only ASCII characters are lowercased; with character set OCTETS/(VAR)BINARY, the entire string is returned unchanged.

8.3.13.1LOWER Examples

  |select Sheriff from Towns
  |  where lower(Name) = 'cooper''s valley'

See alsoSection 8.3.26, “UPPER()

8.3.14LPAD()

Left-pads a string

Result typeVARCHAR or BLOB

Syntax

  |LPAD (str, endlen [, padstr])

Table 8.43LPAD Function Parameters
ParameterDescription

str

An expression of a string type

endlen

Output string length

padstr

The character or string to be used to pad the source string up to the specified length. Default is space (' ')

Left-pads a string with spaces or with a user-supplied string until a given length is reached.

  • This function fully supports text BLOBs of any length and character set.

  • If str is a BLOB, the result is a BLOB. Otherwise, the result is a VARCHAR(endlen).

  • If padstr is given and equal to '' (empty string), no padding takes place.

  • If endlen is less than the current string length, the string is truncated to endlen, even if padstr is the empty string.

🛑
Warning

When used on a BLOB, this function may need to load the entire object into memory. Although it does try to limit memory consumption, this may affect performance if huge BLOBs are involved.

8.3.14.1LPAD Examples

  |lpad ('Hello', 12)               -- returns '       Hello'
  |lpad ('Hello', 12, '-')          -- returns '-------Hello'
  |lpad ('Hello', 12, '')           -- returns 'Hello'
  |lpad ('Hello', 12, 'abc')        -- returns 'abcabcaHello'
  |lpad ('Hello', 12, 'abcdefghij') -- returns 'abcdefgHello'
  |lpad ('Hello', 2)                -- returns 'He'
  |lpad ('Hello', 2, '-')           -- returns 'He'
  |lpad ('Hello', 2, '')            -- returns 'He'

See alsoSection 8.3.21, “RPAD()

8.3.15OCTET_LENGTH()

Length in bytes (octets) of a string or binary value

Result typeINTEGER, or BIGINT for BLOB

Syntax

  |OCTET_LENGTH (string)

Table 8.44OCTET_LENGTH Function Parameter
ParameterDescription

string

An expression of a string type

Gives the length in bytes (octets) of the input string. For multibyte character sets, this may be less than the number of characters times the formal number of bytes per character as found in RDB$CHARACTER_SETS.

With arguments of type CHAR or BINARY, this function takes the entire formal string length (i.e. the declared length of a field or variable) into account. If you want to obtain the logical byte length, not counting the trailing spaces, right-TRIM the argument before passing it to OCTET_LENGTH.

8.3.15.1OCTET_LENGTH Examples

   |select octet_length('Hello!') from rdb$database
   |-- returns 6
   | 
   |select octet_length(_iso8859_1 'Grüß di!') from rdb$database
   |-- returns 8: ü and ß take up one byte each in ISO8859_1
   | 
   |select octet_length
   |  (cast (_iso8859_1 'Grüß di!' as varchar(24) character set utf8))
   |from rdb$database
   |-- returns 10: ü and ß take up two bytes each in UTF8
   | 
   |select octet_length
   |  (cast (_iso8859_1 'Grüß di!' as char(24) character set utf8))
   |from rdb$database
   |-- returns 26: all 24 CHAR positions count, and two of them are 2-byte

See alsoSection 8.3.5, “BIT_LENGTH(), Section 8.3.7, “CHAR_LENGTH(), CHARACTER_LENGTH()

8.3.16OVERLAY()

Overwrites part of, or inserts into, a string

Result typeVARCHAR or BLOB

Syntax

  |OVERLAY (string PLACING replacement FROM pos [FOR length])

Table 8.45OVERLAY Function Parameters
ParameterDescription

string

The string into which the replacement takes place

replacement

Replacement string

pos

The position from which replacement takes place (starting position)

length

The number of characters that are to be overwritten

By default, the number of characters removed from (overwritten in) the host string equals the length of the replacement string. With the optional fourth argument, a different number of characters can be specified for removal.

  • This function supports BLOBs of any length.

  • If string or replacement is a BLOB, the result is a BLOB. Otherwise, the result is a VARCHAR(n) with n the sum of the lengths of string and replacement.

  • As usual in SQL string functions, pos is 1-based.

  • If pos is beyond the end of string, replacement is placed directly after string.

  • If the number of characters from pos to the end of string is smaller than the length of replacement (or than the length argument, if present), string is truncated at pos and replacement placed after it.

  • The effect of a FOR 0 clause is that replacement is inserted into string.

  • If any argument is NULL, the result is NULL.

  • If pos or length is not a whole number, bankers' rounding (round-to-even) is applied, i.e. 0.5 becomes 0, 1.5 becomes 2, 2.5 becomes 2, 3.5 becomes 4, etc.

🛑
Warning

When used on a BLOB, this function may need to load the entire object into memory. This may affect performance if huge BLOBs are involved.

8.3.16.1OVERLAY Examples

   |overlay ('Goodbye' placing 'Hello' from 2)   -- returns 'GHelloe'
   |overlay ('Goodbye' placing 'Hello' from 5)   -- returns 'GoodHello'
   |overlay ('Goodbye' placing 'Hello' from 8)   -- returns 'GoodbyeHello'
   |overlay ('Goodbye' placing 'Hello' from 20)  -- returns 'GoodbyeHello'
   | 
   |overlay ('Goodbye' placing 'Hello' from 2 for 0) -- r. 'GHellooodbye'
   |overlay ('Goodbye' placing 'Hello' from 2 for 3) -- r. 'GHellobye'
   |overlay ('Goodbye' placing 'Hello' from 2 for 6) -- r. 'GHello'
   |overlay ('Goodbye' placing 'Hello' from 2 for 9) -- r. 'GHello'
   | 
   |overlay ('Goodbye' placing '' from 4)        -- returns 'Goodbye'
   |overlay ('Goodbye' placing '' from 4 for 3)  -- returns 'Gooe'
   |overlay ('Goodbye' placing '' from 4 for 20) -- returns 'Goo'
   | 
   |overlay ('' placing 'Hello' from 4)          -- returns 'Hello'
   |overlay ('' placing 'Hello' from 4 for 0)    -- returns 'Hello'
   |overlay ('' placing 'Hello' from 4 for 20)   -- returns 'Hello'

See alsoSection 8.3.18, “REPLACE()

8.3.17POSITION()

Finds the position of the first or next occurrence of a substring in a string

Result typeINTEGER

Syntax

  |  POSITION (substr IN string)
  || POSITION (substr, string [, startpos])

Table 8.46POSITION Function Parameters
ParameterDescription

substr

The substring whose position is to be searched for

string

The string which is to be searched

startpos

The position in string where the search is to start

Returns the (1-based) position of the first occurrence of a substring in a host string. With the optional third argument, the search starts at a given offset, disregarding any matches that may occur earlier in the string. If no match is found, the result is 0.

Note
  • The optional third argument is only supported in the second syntax (comma syntax).

  • The empty string is considered a substring of every string. Therefore, if substr is '' (empty string) and string is not NULL, the result is:

    • 1 if startpos is not given;

    • startpos if startpos lies within string;

    • 0 if startpos lies beyond the end of string.

  • This function fully supports text BLOBs of any size and character set.

🛑
Warning

When used on a BLOB, this function may need to load the entire object into memory. This may affect performance if huge BLOBs are involved.

8.3.17.1POSITION Examples

  |position ('be' in 'To be or not to be')   -- returns 4
  |position ('be', 'To be or not to be')     -- returns 4
  |position ('be', 'To be or not to be', 4)  -- returns 4
  |position ('be', 'To be or not to be', 8)  -- returns 17
  |position ('be', 'To be or not to be', 18) -- returns 0
  |position ('be' in 'Alas, poor Yorick!')   -- returns 0

See alsoSection 8.3.22, “SUBSTRING()

8.3.18REPLACE()

Replaces all occurrences of a substring in a string

Result typeVARCHAR or BLOB

Syntax

  |REPLACE (str, find, repl)

Table 8.47REPLACE Function Parameters
ParameterDescription

str

The string in which the replacement is to take place

find

The string to search for

repl

The replacement string

  • This function fully supports text BLOBs of any length and character set.

  • If any argument is a BLOB, the result is a BLOB. Otherwise, the result is a VARCHAR(n) with n calculated from the lengths of str, find and repl in such a way that even the maximum possible number of replacements won’t overflow the field.

  • If find is the empty string, str is returned unchanged.

  • If repl is the empty string, all occurrences of find are deleted from str.

  • If any argument is NULL, the result is always NULL, even if nothing would have been replaced.

🛑
Warning

When used on a BLOB, this function may need to load the entire object into memory. This may affect performance if huge BLOBs are involved.

8.3.18.1REPLACE Examples

  |replace ('Billy Wilder',  'il', 'oog') -- returns 'Boogly Woogder'
  |replace ('Billy Wilder',  'il',    '') -- returns 'Bly Wder'
  |replace ('Billy Wilder',  null, 'oog') -- returns NULL
  |replace ('Billy Wilder',  'il',  null) -- returns NULL
  |replace ('Billy Wilder', 'xyz',  null) -- returns NULL (!)
  |replace ('Billy Wilder', 'xyz', 'abc') -- returns 'Billy Wilder'
  |replace ('Billy Wilder',    '', 'abc') -- returns 'Billy Wilder'

See alsoSection 8.3.16, “OVERLAY(), Section 8.3.22, “SUBSTRING(), Section 8.3.17, “POSITION(), Section 8.3.7, “CHAR_LENGTH(), CHARACTER_LENGTH()

8.3.19REVERSE()

Reverses a string

Result typeVARCHAR

Syntax

  |REVERSE (string)

Table 8.48REVERSE Function Parameter
ParameterDescription

string

An expression of a string type

8.3.19.1REVERSE Examples

  |reverse ('spoonful')            -- returns 'lufnoops'
  |reverse ('Was it a cat I saw?') -- returns '?was I tac a ti saW'
Tip

This function is useful if you want to group, search or order on string endings, e.g. when dealing with domain names or email addresses:

  |create index ix_people_email on people
  |  computed by (reverse(email));
  | 
  |select * from people
  |  where reverse(email) starting with reverse('.br');

8.3.20RIGHT()

Extracts the rightmost part of a string

Result typeVARCHAR or BLOB

Syntax

  |RIGHT (string, length)

Table 8.49RIGHT Function Parameters
ParameterDescription

string

An expression of a string type

length

Integer. The number of characters to return

  • This function supports text BLOBs of any length.

  • If string is a BLOB, the result is a BLOB. Otherwise, the result is a VARCHAR(n) with n the length of the input string.

  • If the length argument exceeds the string length, the input string is returned unchanged.

  • If the length argument is not a whole number, bankers' rounding (round-to-even) is applied, i.e. 0.5 becomes 0, 1.5 becomes 2, 2.5 becomes 2, 3.5 becomes 4, etc.

🛑
Warning

When used on a BLOB, this function may need to load the entire object into memory. This may affect performance if huge BLOBs are involved.

See alsoSection 8.3.12, “LEFT(), Section 8.3.22, “SUBSTRING()

8.3.21RPAD()

Right-pads a string

Result typeVARCHAR or BLOB

Syntax

  |RPAD (str, endlen [, padstr])

Table 8.50RPAD Function Parameters
ParameterDescription

str

An expression of a string type

endlen

Output string length

endlen

The character or string to be used to pad the source string up to the specified length. Default is space (' ')

Right-pads a string with spaces or with a user-supplied string until a given length is reached.

  • This function fully supports text BLOBs of any length and character set.

  • If str is a BLOB, the result is a BLOB. Otherwise, the result is a VARCHAR(endlen).

  • If padstr is given and equals '' (empty string), no padding takes place.

  • If endlen is less than the current string length, the string is truncated to endlen, even if padstr is the empty string.

🛑
Warning

When used on a BLOB, this function may need to load the entire object into memory. Although it does try to limit memory consumption, this may affect performance if huge BLOBs are involved.

8.3.21.1RPAD Examples

  |rpad ('Hello', 12)               -- returns 'Hello       '
  |rpad ('Hello', 12, '-')          -- returns 'Hello-------'
  |rpad ('Hello', 12, '')           -- returns 'Hello'
  |rpad ('Hello', 12, 'abc')        -- returns 'Helloabcabca'
  |rpad ('Hello', 12, 'abcdefghij') -- returns 'Helloabcdefg'
  |rpad ('Hello', 2)                -- returns 'He'
  |rpad ('Hello', 2, '-')           -- returns 'He'
  |rpad ('Hello', 2, '')            -- returns 'He'

See alsoSection 8.3.14, “LPAD()

8.3.22SUBSTRING()

Extracts a substring by position and length, or by SQL regular expression

Result typesVARCHAR or BLOB

Syntax

   |SUBSTRING ( <substring-args> )
   | 
   |<substring-args> ::=
   |    str FROM startpos [FOR length]
   |  | str SIMILAR <similar-pattern> ESCAPE <escape>
   | 
   |<similar-pattern> ::=
   |  <similar-pattern-R1>
   |  <escape> " <similar-pattern-R2> <escape> "
   |  <similar-pattern-R3>

Table 8.51SUBSTRING Function Parameters
ParameterDescription

str

An expression of a string type

startpos

Integer expression, the position from which to start retrieving the substring

length

The number of characters to retrieve after the startpos

similar-pattern

SQL regular expression pattern to search for the substring

escape

Escape character

Returns a string’s substring starting at the given position, either to the end of the string or with a given length, or extracts a substring using an SQL regular expression pattern.

If any argument is NULL, the result is also NULL.

🛑
Warning

When used on a BLOB, this function may need to load the entire object into memory. Although it does try to limit memory consumption, this may affect performance if huge BLOBs are involved.

8.3.22.1Positional SUBSTRING

In its simple, positional form (with FROM), this function returns the substring starting at character position startpos (the first character being 1). Without the FOR argument, it returns all the remaining characters in the string. With FOR, it returns length characters or the remainder of the string, whichever is shorter.

When startpos is smaller than 1, substring behaves as if the string has 1 - startpos extra positions before the actual first character at position 1. The length is considered from this imaginary start of the string, so the resulting string could be shorter than the specified length, or even empty.

The function fully supports binary and text BLOBs of any length, and with any character set. If str is a BLOB, the result is also a BLOB. For any other argument type, the result is a VARCHAR.

For non-BLOB arguments, the width of the result field is always equal to the length of str, regardless of startpos and length. So, substring('pinhead' from 4 for 2) will return a VARCHAR(7) containing the string 'he'.

Example

   |insert into AbbrNames(AbbrName)
   |  select substring(LongName from 1 for 3) from LongNames;
   | 
   |select substring('abcdef' from 1 for 2) from rdb$database;
   |-- result: 'ab'
   | 
   |select substring('abcdef' from 2) from rdb$database;
   |-- result: 'bcdef'
   | 
   |select substring('abcdef' from 0 for 2) from rdb$database;
   |-- result: 'a'
   |-- and NOT 'ab', because there is "nothing" at position 0
   | 
   |select substring('abcdef' from -5 for 2) from rdb$database;
   |-- result: ''
   |-- length ends before the actual start of the string

8.3.22.2Regular Expression SUBSTRING

In the regular expression form (with SIMILAR), the SUBSTRING function returns part of the string matching an SQL regular expression pattern. If no match is found, NULL is returned.

The SIMILAR pattern is formed from three SQL regular expression patterns, R1, R2 and R3. The entire pattern takes the form of R1 || '<escape>"' || R2 || '<escape>"' || R3, where <escape> is the escape character defined in the ESCAPE clause. R2 is the pattern that matches the substring to extract, and is enclosed between escaped double quotes (<escape>", e.g. #" with escape character #). R1 matches the prefix of the string, and R3 the suffix of the string. Both R1 and R3 are optional (they can be empty), but the pattern must match the entire string. In other words, it is not sufficient to specify a pattern that only finds the substring to extract.

The escaped double quotes around R2 can be compared to defining a single capture group in more common regular expression syntax like PCRE. That is, the full pattern is equivalent to R1(R2)R3, which must match the entire input string, and the capture group is the substring to be returned.

If any one of R1, R2, or R3 is not a zero-length string and does not have the format of an SQL regular expression, then an exception is raised.

The full SQL regular expression format is described in Syntax: SQL Regular Expressions

Examples

  |substring('abcabc' similar 'a#"bcab#"c' escape '#')  -- bcab
  |substring('abcabc' similar 'a#"%#"c' escape '#')     -- bcab
  |substring('abcabc' similar '_#"%#"_' escape '#')     -- bcab
  |substring('abcabc' similar '#"(abc)*#"' escape '#')  -- abcabc
  |substring('abcabc' similar '#"abc#"' escape '#')     -- <null>

See alsoSection 8.3.17, “POSITION(), Section 8.3.12, “LEFT(), Section 8.3.20, “RIGHT(), Section 8.3.7, “CHAR_LENGTH(), CHARACTER_LENGTH(), SIMILAR TO

8.3.23TRIM()

Trims leading and/or trailing spaces or other substrings from a string

Result typeVARCHAR or BLOB

Syntax

  |TRIM ([<adjust>] str)
  | 
  |<adjust> ::=  {[<where>] [what]} FROM
  | 
  |<where> ::=  BOTH | LEADING | TRAILING

Table 8.52TRIM Function Parameters
ParameterDescription

str

An expression of a string type

where

The position the substring is to be removed from — BOTH | LEADING | TRAILING. BOTH is the default

what

The substring that should be removed (multiple times if there are several matches) from the beginning, the end, or both sides of the input string str. By default, it is space (' ')

Removes leading and/or trailing spaces (or optionally other strings) from the input string.

If str is a BLOB, the result is a BLOB. Otherwise, it is a VARCHAR(n) with n the formal length of str.

🛑
Warning

When used on a BLOB, this function may need to load the entire object into memory. This may affect performance if huge BLOBs are involved.

8.3.23.1TRIM Examples

   |select trim ('  Waste no space   ') from rdb$database
   |-- returns 'Waste no space'
   | 
   |select trim (leading from '  Waste no space   ') from rdb$database
   |-- returns 'Waste no space   '
   | 
   |select trim (leading '.' from '  Waste no space   ') from rdb$database
   |-- returns '  Waste no space   '
   | 
   |select trim (trailing '!' from 'Help!!!!') from rdb$database
   |-- returns 'Help'
   | 
   |select trim ('la' from 'lalala I love you Ella') from rdb$database
   |-- returns ' I love you El'
   | 
   |select trim ('la' from 'Lalala I love you Ella') from rdb$database
   |-- returns 'Lalala I love you El'

8.3.24UNICODE_CHAR()

Character from Unicode code point

Result typeCHAR(1) CHARACTER SET UTF8

Syntax

  |UNICODE_CHAR (code)

Table 8.53UNICODE_CHAR Function Parameter
ParameterDescription

code

The Unicode code point (range 0…​0x10FFFF)

Returns the character corresponding to the Unicode code point passed in the argument.

See alsoSection 8.3.25, “UNICODE_VAL(), Section 8.3.1, “ASCII_CHAR()

8.3.25UNICODE_VAL()

Unicode code point from string

Result typeINTEGER

Syntax

  |UNICODE_VAL (ch)

Table 8.54UNICODE_VAL Function Parameter
ParameterDescription

ch

A string of the [VAR]CHAR data type or a text BLOB

Returns the Unicode code point (range 0…​0x10FFFF) of the character passed in.

  • If the argument is a string with more than one character, the Unicode code point of the first character is returned.

  • If the argument is an empty string, 0 is returned.

  • If the argument is NULL, NULL is returned.

See alsoSection 8.3.24, “UNICODE_CHAR(), Section 8.3.2, “ASCII_VAL()

8.3.26UPPER()

Converts a string to uppercase

Result type(VAR)CHAR, (VAR)BINARY or BLOB

Syntax

  |UPPER (str)

Table 8.55UPPER Function Parameter
ParameterDescription

str

An expression of a string type

Returns the uppercase equivalent of the input string. The exact result depends on the character set. With ASCII or NONE for instance, only ASCII characters are uppercased; with character set OCTETS/(VAR)BINARY, the entire string is returned unchanged.

8.3.26.1UPPER Examples

  |select upper(_iso8859_1 'Débâcle')
  |from rdb$database
  |-- returns 'DÉBÂCLE'
  | 
  |select upper(_iso8859_1 'Débâcle' collate fr_fr)
  |from rdb$database
  |-- returns 'DEBACLE', following French uppercasing rules

See alsoSection 8.3.13, “LOWER()