Monday, January 23, 2023

Escaping Single Quotes in Db2 SQL Statements

Every now and then I write about some things that may seem to be basic to old-timers, but can be very confusing to developers the first time they encounter them. Today's post is an example.

How do you handle a text string with a single quote in it? For example, something like this:

    Today is Craig's birthday (not really)

Well, the first thing to corroborate is that text in Db2 SQL is delimited by single quotes. So the first attempt people tend to make is something like this:

    'Today is Craig's birthday (not really)'

But they also quickly discover that this does not work. There are three single quotes here: one at the beginning, one between the "g" and the "s", and one at the end. So Db2 will choke on it and you will get an error.

The trick is knowing the escape character. An "escape" character is used to tell Db2 that the next character is actually part of the text string, not a delimiter. For Db2, the escape is to double up the single quote (note that other DBMSes may use a different technique). So, if we want to use our sample text phrase in Db2 SQL, we'd code it with the escape character, as follows:

    'Today is Craig''s birthday (not really)'

The single quote denoting the possessive for Craig's is doubled. This tells Db2 to treat the single quote as part of the text. So we could write SQL like this:

    SELECT 'Today is Craig''s birthday (not really)'

This will return the text that we want:

    Today is Craig's birthday (not really)

This works even if there are multiple single quotes within the text. For example, consider if we want to use the following text in SQL:

    Today is not Craig's birthday but it is Beth's

We could write the SQL like this:

    SELECT 'Today is not Craig''s birthday but it is Beth''s'

And it also works even at the end of the text string, even though it starts to look somewhat confusing. For example, what is we want to use the following text in SQL?

    I like the book 'A Confederacy of Dunces'

In that case, we still double up the single quotes, like so:

    SELECT 'I like ths book ''A Confederacy of Dunces'''

And that will return our desired text.

I hope this short treatise on how to use the escape for single quotes in Db2 SQL has been helpful!