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SUBSTRING

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Extracts a range of characters from a string.

Syntax

SUBSTRING(str, start, len)
SUBSTR(str, start, len)
SUBSTRING(str, start)
SUBSTR(str, start)
SUBSTRING(str FROM start FOR len)
SUBSTR(str FROM start FOR len)
SUBSTRING(str FROM start)
SUBSTR(str FROM start)

Arguments

  • str: any string or binary object

  • start: the one-indexed position to start at. If negative, counts from the end.

  • len: length is the number of characters to extract. Forms without len, extract characters until the end of the string.

Return Type

String

Remarks

  • In SUBSTR or SUBSTRING, the starting index point of a string is 1 (0 is an alias for 1).

Examples

In the following example, the starting index 3 represents the third character in the string, because the index starts from 1.

SELECT SUBSTRING('1234567890', 3, 3);
+-------------------------------+
| SUBSTRING('1234567890', 3, 3) |
+-------------------------------+
| 345                           |
+-------------------------------+

In the following example, the substring is returned from the end, because the starting index is a negative number.

SELECT SUBSTRING('1234567890', -3, 3);
+--------------------------------+
| SUBSTRING('1234567890', -3, 3) |
+--------------------------------+
| 890                            |
+--------------------------------+

The following examples demonstrate how substring works using different lengths and starting positions. The table and values for these examples are included.

CREATE TABLE sub_tab(a INT, b INT, c INT, d INT);


INSERT INTO sub_tab VALUES(1234,1234,1234,1234),(1,2,4, NULL);
SELECT substr(a,0,1) FROM sub_tab;
+---------------+
| substr(a,0,1) |
+---------------+
| 1             |
| 1             |
+---------------+
SELECT substr(a,1,1) FROM sub_tab;
+---------------+
| substr(a,1,1) |
+---------------+
| 1             |
| 1             |
+---------------+
SELECT substr(a,1,2) FROM sub_tab;
+---------------+
| substr(a,1,2) |
+---------------+
| 1             |
| 12            |
+---------------+
SELECT substr(a,0,2) FROM sub_tab;
+---------------+
| substr(a,0,2) |
+---------------+
| 12            |
| 1             |
+---------------+

Caution

Implicit Collation

When character_set_server is set to utf8, string literals with characters using 4-byte encoding are implicitly assigned binary collation and processed as a sequence of bytes rather than characters. This implicit conversion to binary collation causes string functions to return unexpected results. To avoid using implicit binary collation, either use explicit type casting or use database columns defined with the utf8mb4 character set.

For more information, refer to Implicit Collation in Special Cases.

Related Topics

Last modified: June 12, 2023

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