Beginning SQL

Chapter 5
The TRIM() Functions
Trimming involves removing unwanted characters from the beginning or end of a string. In most
database implementations, the only character that can be trimmed is the space. However, trimming
spaces is very useful with a character data type column. A variable character column stores only the
number of characters you ask it to store; however, a nonvarying character column pads out the string
with spaces if the string being stored is less than the maximum number of characters the column can
store.
For example, define a new table using the following SQL:
CREATE TABLE MyTable
(
first_column char(80)
);
The column first_column can hold up to 80 characters. Now, consider this INSERT statement:
INSERT INTO MyTable (first_column)
VALUES (‘ABC’);
ABC plus seven blank spaces is stored. If you want the results to return only the characters you inserted and
no spaces, you can trim off the spaces with one of the two trim functions: LTRIM() or RTRIM(). LTRIM()
removes any spaces on the left of the characters, while RTRIM() removes any spaces on the right of the
characters. So, if you want to remove the trailing spaces from the example table defined previously, you
would use RTRIM():
SELECT first_column, RTRIM(first_column)
FROM MyTable;
The results for this are as follows:
first_column RTRIM(first_column)
ABC ABC
Notice that first_column is a lot wider than RTRIM(first_column) due to the extra spaces. Note also
that some database systems don’t display the spaces even when they’re there. You no longer need
MyTable, so delete it by running the following code:
DROP TABLE MyTable;
Your next stop on the tour of string functions is the function to find how many characters there are in a
string — finally, a definitive answer to the question, “How long is a piece of string?”
The LENGTH() Function
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Sometimes it can be very useful to find out how many characters there are in a string. Oracle, IBM, and
MySQL use the LENGTH() function to find out how long a string is. MS Access and MS SQL Server use
the LEN() function, which does the same thing and works the same way.