The dataflow text editor is pretty simple compared to other SQL enabled text editors out there. You get to type your query without much assistance like you might find elsewhere. On the plus side, however, there is some highlighting for reserved words (purple) and datatypes (green for numbers, red for strings):

Additionally, there is also a lesser-known autofill mechanism which can prove to save time and frustration.
Want to insert the table name instead of copy/pasting or typing it? Type the first letter and then hit CTRL+SPACE and see your input datasets that start with that letter:

Did you also notice FROM in the list? That's because this same shortcut key works for many reserved words as well, and I started with the letter F, so I'm seeing all of the tables and reserved words starting with F. But you don't have to type the first letter. Hit CTRL+SPACE without any hints and see all of the autofill options, which include all of the dataflow reserved words as well as all of your input datasets. The drop down list actively filters as you type:

And my favorite (though this is a bit buggier), load up your column names if you can't remember exactly what they are:

For this last one, you have to alias your tables and provide the alias and dot operator first, then hit CTRL+SPACE, before you see the column names. It does seem to be finicky and doesn't always work, but is pretty helpful when it does.
For you SQL dataflow people, try this out and comment below with any additional features you find.