SUBSTRING

The SUBSTRING function returns a substring of a string.

expression

An expression that specifies the string from which the result is derived.

Expression must be any built-in numeric or string data type. A numeric argument is cast to a character string before evaluating the function. For more information about converting numeric to a character string, see VARCHAR. If expression is a character string, the result of the function is a character string. If it is a graphic string, the result of the function is a graphic string. If it is a binary string, the result of the function is a binary string.

A substring of expression is zero or more contiguous characters of expression. If expression is a graphic string, a character is a DBCS or Unicode graphic character. If expression is a character string, a character is a character that may consist of one or more bytes. If expression is a binary string, a character is a byte.

start

An expression that specifies the position within expression of the first character (or byte) of the result. The expression must return a value that is a built-in BIGINT, INTEGER, or SMALLINT data type. A value of 1 indicates that the first character of the result is the first character of expression. A negative or zero value indicates a position before the beginning of the string. It may also be greater than the length attribute of expression. (The length attribute of a varying-length string is its maximum length.)

length

An expression that specifies the maximum actual length of the resulting substring. If specified, length must be an expression that returns a value that is a built-in BIGINT, INTEGER, or SMALLINT data type. The value must be greater than or equal to 0.

If length is explicitly specified, padding is not performed.

If expression is a fixed-length string, omission of length is an implicit specification of LENGTH(expression) - start + 1, which is the number of characters (or bytes) from the start character (or byte) to the last character (or byte) of expression. If expression is a varying-length string, omission of length is an implicit specification of zero or LENGTH(expression) - start + 1, whichever is greater. If the resulting length is zero, the result is the empty string.

The data type of the result depends on the data type of expression:

Data type of expression	Data Type of the Result for SUBSTRING
CHAR or VARCHAR	VARCHAR
CLOB	CLOB
GRAPHIC or VARGRAPHIC	VARGRAPHIC
DBCLOB	DBCLOB
BINARY or VARBINARY	VARBINARY
BLOB	BLOB

The length attribute of the result is the same as the length attribute of expression. (Remember that if the actual length of expression is less than the value for start, the actual length of the substring is zero.)

If any argument can be null, the result can be null; if any argument is null, the result is the null value.

The CCSID of the result is the same as that of expression.

Examples

Select all rows from the PROJECT table for which the project name (PROJNAME) starts with the word 'OPERATION '.
```
  SELECT *
    FROM PROJECT
    WHERE SUBSTRING(PROJNAME,1,10) = 'OPERATION '
```
The space at the end of the constant is necessary to preclude initial words such as 'OPERATIONS'.
Assume that FIRSTNAME is a VARCHAR(12) column, encoded in Unicode UTF-8, in T1. One of its values is the 6-character string 'Jürgen'. When FIRSTNAME has this value:
```
  SELECT SUBSTRING(FIRSTNAME, 1,2), SUBSTR(FIRSTNAME, 1,2)
    FROM T1
```
Returns the values 'Jü' (x'4AC3BC') and 'Jô' (x'4AC3').