This topic describes how to use the string function SUBSTRING in Realtime Compute.

## Syntax

``````VARCHAR SUBSTRING(VARCHAR a, INT start)
VARCHAR SUBSTRING(VARCHAR a, INT start, INT len)      ``````

## Input parameters

Parameter Data type Description
a VARCHAR The source string.
start INT The start position of the substring that you want to extract from the source string.
len INT The length of the substring that you want to extract.

## Description

Returns a substring of the specified length from the source string. The substring starts from the specified position. If the length is not specified, this function returns a substring starting from the specified position to the end of the string. In most cases, the value of the start parameter is an integer greater than or equal to 1. If the value is 0, it is regarded as 1. If the value is negative, this function counts backward from the end of the string to find the first character of the substring.

## Example

• Test data
str (VARCHAR) nullstr (VARCHAR)
k1=v1;k2=v2 null
• Test statements
``````SELECT SUBSTRING('', 222222222) as var1,
SUBSTRING(str, 2) as var2,
SUBSTRING(str, -2) as var3,
SUBSTRING(str, -2, 1) as var4,
SUBSTRING(str, 2, 1) as var5,
SUBSTRING(str, 22) as var6,
SUBSTRING(str, -22) as var7,
SUBSTRING(str, 1) as var8,
SUBSTRING(str, 0) as var9,
SUBSTRING(nullstr, 0) as var10
FROM T1;         ``````
• Test results
var1 (VARCHAR) var2 (VARCHAR) var3 (VARCHAR) var4 (VARCHAR) var5 (VARCHAR) var6 (VARCHAR) var7 (VARCHAR) var8 (VARCHAR) var9 (VARCHAR) var10 (VARCHAR)
null 1=v1;k2=v2 v2 v 1 null null k1=v1;k2=v2 k1=v1;k2=v2 null