substr/substring

This function is used to return the substring of str, starting from start_position and with a length of length.

substr(string <str>, bigint <start_position>[, bigint <length>])

substring(string <str>, bigint <start_position>[, bigint <length>])

**Table 1** Parameters
Parameter	Mandatory	Type	Description
str	Yes	STRING	If the value is of the BIGINT, DECIMAL, DOUBLE, or DATETIME type, the value is implicitly converted to the STRING type for calculation.
start_position	Yes	BIGINT	Start position. The default value is 1. If the value is positive, the substring is returned from the left. If the value is negative, the substring is returned from the right.
length	No	BIGINT	Length of the substring. The value must be greater than 0.

The return value is of the STRING type.

If the value of str is not of the STRING, BIGINT, DECIMAL, DOUBLE, or DATETIME type, an error is reported.
If the value of length is not of the BIGINT type or is less than or equal to 0, an error is reported.
When the length parameter is omitted, a substring that ends with str is returned.
If the value of str, start_position, or length is NULL, NULL is returned.