How Can I Sort String Columns with Embedded Numbers in SQL?

Sorting String Columns with Embedded Numbers in SQL

Sorting string columns containing numbers in SQL can present challenges. The natural sorting algorithm of many databases places numbers in the wrong order, such as placing "a 12" after "a 1". This behavior is acceptable for most applications, but it can be undesirable for specific needs.

Is it possible to sort string columns with embedded numbers using pure SQL?

SOLUTION

Assuming the column follows a specific pattern of "WORD space NUMBER," the following code snippet can be used to sort the column correctly:

SELECT *
FROM table
ORDER BY CAST(SUBSTRING(column,LOCATE(' ',column)+1) AS SIGNED)

Here's how it works:

• LOCATE(' ',column) finds the position of the space character in the string.
• SUBSTRING(column,LOCATE(' ',column) 1) extracts the number portion of the string after the space.
• CAST(... AS SIGNED) converts the extracted number to a signed integer for comparison.

PROOF OF CONCEPT

The following examples demonstrate the sorting behavior:

mysql> INSERT INTO t (st) VALUES ('a 1'),('a 12'),('a 6'),('a 11');
mysql> SELECT * FROM t ORDER BY st;
mysql> SELECT * FROM t ORDER BY CAST(SUBSTRING(st,LOCATE(' ',st)+1) AS SIGNED);

The second query sorts the results correctly, placing "a 1" before "a 12".

CONSIDERATIONS

If the column pattern differs from "WORD space NUMBER," a different workaround may be required.

ENHANCEMENTS

The following enhanced query adds a double sort to break letter prefixes with numeric values:

ORDER BY SUBSTRING_INDEX(st, " ", 1) ASC, CAST(SUBSTRING_INDEX(st, " ", -1) AS SIGNED)

This modified code snippet provides a more comprehensive sorting solution.

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