SQLite Substr

The SQLite substr function returns a substring from a string starting at a specified position with a predefined length.

Syntax

substr( string, start, length )Code language: SQL (Structured Query Language) (sql)

The starting position of the substring is determined by the start argument and its length is determined by the length argument.

Arguments

The substr() function accepts three arguments.

string

The string to be used to extract the substring.

start

The start argument is an integer that specifies the starting position of the returned substring. The start argument can be a positive or negative integer

• If the start is a positive integer, the  substr() function returns a substring starting from the beginning of the string. The first character has an index of 1.
• If the start is a negative integer, the returned substring consists of the length number of character starting from the end of the string. The last character has an index of -1.

See the following picture of a sample string with the positive and negative start

length

The length argument determines the length of the substring. The length argument is optional. If it is omitted, it is assumed to be the maximum positive integer.

If any argument is NULL, the  substr() function will return NULL.

Return Type

TEXT

Examples

See the following string:

The following statement extracts and returns a substring from the SQLite substr string:

SELECT substr('SQLite substr', 1, 6);Code language: SQL (Structured Query Language) (sql)

substr('SQLite substr', 1, 6)
-----------------------------
SQLite

The following statement returns a substring from a string using a negative start argument.

SELECT substr('SQLite substr', - 6, 6);Code language: SQL (Structured Query Language) (sql)

substr('SQLite substr', -6, 6)
-----------------------------
substrCode language: SQL (Structured Query Language) (sql)

The following statement illustrates how to use the substr() function with a negative length argument.

SELECT substr('SQLite substr', 7, -6)Code language: SQL (Structured Query Language) (sql)

substr('SQLite substr', 7, -6)
-----------------------------
SQLiteCode language: SQL (Structured Query Language) (sql)

The following statement demonstrates how to use the substr function with only the first two arguments, the length argument is omitted.

SELECT substr('SQLite substr', 8);Code language: SQL (Structured Query Language) (sql)

substr('SQLite substr', 8)
-----------------------------
substrCode language: SQL (Structured Query Language) (sql)

The following statement returns all track names from the tracks table in the sample database. It sorts the track names by their lengths:

SELECT
	Name
FROM
	tracks
ORDER BY
	LENGTH(name) DESC;Code language: SQL (Structured Query Language) (sql)

Here is the partial output:

The following statement uses the substr() function to get only the first 20 characters of the track names if the lengths of the names are more than 20; otherwise, it returns the whole names:

SELECT 
	CASE 
		WHEN LENGTH(Name) > 20 THEN 
			substr(Name,1,20) || '...'
		ELSE
			Name 
		END ShortName
FROM 
	tracks
ORDER BY 
	LENGTH(name) DESC;Code language: SQL (Structured Query Language) (sql)

This picture illustrates the partial output:

Note that if lengths of track names are greater than 20, they are concatenated with the string "...".