DB2 Version 9.7 for Linux, UNIX, and Windows

SUBSTR scalar function


>>-SUBSTR--(--string--,--start--+-----------+--)---------------><
                                '-,--length-'

The schema is SYSIBM.

The SUBSTR function returns a substring of a string.

string: An expression that specifies the string from which the result is derived.
The expression must return a value that is a built-in string, numeric, or datetime data type. If the value is not a string data type, it is implicitly cast to VARCHAR before evaluating the function. If string is either a character string or a binary string, a substring of string is zero or more contiguous bytes of string. If string is a graphic string, a substring of string is zero or more contiguous double-byte characters of string.
start: An expression that specifies the position of the first byte of the result for a character string or a binary string or the position of the first character of the result for a graphic string. The expression must return a value that is a built-in numeric, CHAR, VARCHAR, GRAPHIC, or VARGRAPHIC data type. If the value is not of type INTEGER, it is implicitly cast to INTEGER before evaluating the function. The integer value must be between 1 and the length or maximum length of string, depending on whether string is fixed-length or varying-length (SQLSTATE 22011, if out of range). It must be specified as number of bytes in the context of the database code page and not the application code page.
length: An expression that specifies the length of the result. If specified, the expression must return a value that is a built-in numeric, CHAR, VARCHAR, GRAPHIC, or VARGRAPHIC data type. If the value is not of type INTEGER, it is implicitly cast to INTEGER before evaluating the function. The value of the integer must be in the range of 0 to n, where n equals (the length attribute of string) - start + 1 (SQLSTATE 22011, if out of range).
If length is explicitly specified, string is effectively padded on the right with the necessary number of blank characters (single-byte for character strings; double-byte for graphic strings) or hexadecimal zero characters (for BLOB strings) so that the specified substring of string always exists. The default for length is the number of bytes from the byte specified by the start to the last byte of string in the case of character string or binary string or the number of double-byte characters from the character specified by the start to the last character of string in the case of a graphic string. However, if string is a varying-length string with a length less than start, the default is zero and the result is the empty string. It must be specified as number of bytes in the context of the database code page and not the application code page. (For example, the column NAME with a data type of VARCHAR(18) and a value of 'MCKNIGHT' will yield an empty string with SUBSTR(NAME,10)).

If string is a character string, the result of the function is a character string represented in the code page of its first argument. If it is a binary string, the result of the function is a binary string. If it is a graphic string, the result of the function is a graphic string represented in the code page of its first argument. If the first argument is a host variable that is not a binary string and not a FOR BIT DATA character string, the code page of the result is the database code page. If any argument of the SUBSTR function can be null, the result can be null; if any argument is null, the result is the null value.

Table 1 shows that the result type and length of the SUBSTR function depend on the type and attributes of its inputs.

Table 1. Data Type and Length of SUBSTR Result
String Argument Data Type	Length Argument	Result Data Type
CHAR(A)	constant (l<255)	CHAR(l)
CHAR(A)	not specified but start argument is a constant	CHAR(A-start+1)
CHAR(A)	not a constant	VARCHAR(A)
VARCHAR(A)	constant (l<255)	CHAR(l)
VARCHAR(A)	constant (254<l<32673)	VARCHAR(l)
VARCHAR(A)	not a constant or not specified	VARCHAR(A)
CLOB(A)	constant (l)	CLOB(l)
CLOB(A)	not a constant or not specified	CLOB(A)
GRAPHIC(A)	constant (l<128)	GRAPHIC(l)
GRAPHIC(A)	not specified but start argument is a constant	GRAPHIC(A-start+1)
GRAPHIC(A)	not a constant	VARGRAPHIC(A)
VARGRAPHIC(A)	constant (l<128)	GRAPHIC(l)
VARGRAPHIC(A)	constant (127<l<16337)	VARGRAPHIC(l)
VARGRAPHIC(A)	not a constant	VARGRAPHIC(A)
DBCLOB(A)	constant (l)	DBCLOB(l)
DBCLOB(A)	not a constant or not specified	DBCLOB(A)
BLOB(A)	constant (l)	BLOB(l)
BLOB(A)	not a constant or not specified	BLOB(A)

Note: The LONG VARCHAR and LONG VARGRAPHIC data types continue to be supported but are deprecated and not recommended.

If string is a fixed-length string, omission of length is an implicit specification of LENGTH(string) - start + 1. If string is a varying-length string, omission of length is an implicit specification of zero or LENGTH(string) - start + 1, whichever is greater.

Notes

In dynamic SQL, string, start, and length can be represented by a parameter marker. If a parameter marker is used for string, the data type of the operand will be VARCHAR, and the operand will be nullable.
Though not explicitly stated in the result definitions above, the semantics imply that if string is a mixed single- and multi-byte character string, the result might contain fragments of multi-byte characters, depending upon the values of start and length. For example, the result could possibly begin with the second byte of a multi-byte character, or end with the first byte of a multi-byte character. The SUBSTR function does not detect such fragments, nor provide any special processing should they occur.

Examples

Assume the host variable NAME (VARCHAR(50)) has a value of 'BLUE JAY' and the host variable SURNAME_POS (int) has a value of 6.
```
   SUBSTR(:NAME, :SURNAME_POS)
```
Returns the value 'JAY'
```
   SUBSTR(:NAME, :SURNAME_POS,1)
```
Returns the value 'J'.
Select all rows from the PROJECT table for which the project name (PROJNAME) starts with the word 'OPERATION'.
```
   SELECT * FROM PROJECT
     WHERE SUBSTR(PROJNAME,1,10) = 'OPERATION '
```
The space at the end of the constant is necessary to preclude initial words such as 'OPERATIONS'.