How to write the simplest query result statement

I don't know how to write the simplest query result statement in PHP, but now I only have space in PHP. I want A function. it's very simple. There are two columns in the data table (A & nbsp; & amp; & nbsp; B) implementation: enter A value in the text box, query the value of column B corresponding to this value in column A in the database, and return it to the page. You can help you write the simplest query result statement.
I don't know PHP, but now I only have space for PHP,
To create a function, you can easily,

There are two columns in the data table (A & B)
Implementation: I enter A value in the text box to query the value of column B corresponding to this value in column A in the database and return it to the page.

Yes... can you help me write a relatively complete off-the-shelf statement? Share the following information about database connection statements: More