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The functions we've learned so far act on entire string values. We can also manipulate parts of strings, or even single letters. We'll start with the SUBSTRING() function. It looks like this:

SUBSTRING(text FROM start FOR length)

or the shorter form:

SUBSTRING(text, start, length)

Here's how you'd use it to select part of a string:

SELECT SUBSTRING(name, 5, 4) AS substring_name
FROM item;

The first parameter of SUBSTRING() is the given text (above, the name field). The second parameter tells the function where the substring should start. The indexing is 1-based (the first character in the string is available at index 1).

In the above example, we are asking the SUBSTRING() function to start the text fragment at the fifth character. The third parameter, length, indicates how many characters will be returned.

In this case, if the name is 'TripCare', the starting index is 5, and the length is 4, we'll get 'Care' as the result. The database will start at the fifth character, which is 'C', and return that character and the next three characters.