beginner SQL conditional INSERT INTO question

Here's a pseudo-table:

Table: people
    name : varchar
    is_married : varchar

I have a php variable $selected_individual whose is_married status I need to update. I'm stuck after

SELECT * from people
WHERE name = '$selected_individual'

How do I update his is_married status?

This maybe related to this question but nested queries and JOIN开发者_运维问答 are way to advanced for me to get my head around at this point (I'll look into them after some much needed sleep).

edit: for example in this query,

INSERT INTO x_table(instance, user, item) 
    SELECT 919191, 123, 456
        FROM dual
        WHERE NOT EXISTS (SELECT * FROM x_table
                             WHERE user = 123 
                               AND item = 456)

I can't seem to figure where can I plug in my 'yes' value myself for is_married column. (or where do I put VALUES ('yes') in there?)

update people set is_married = 'Y' where name = '$selected_individual';

While Paul Tomblin has provided a direct answer, I'd like to add the following recommendation and best practices:

• Read a General Introduction to SQL
• Use a primary key
• Prevent SQL Injection