This article assumes that you have read our article on Tables: The Essentials.
The first step in creating an app is adding a table to your app definition. A table is a description of the rows and columns in your spreadsheet. While all of the data is stored in your spreadsheet, this description becomes part of your app definition.
Columns and Rows in AppSheet
Columns: AppSheet reads each column header to define the Column Structure of the app. Every time you change the columns in the spreadsheet, you need to regenerate the column structure within the app, or AppSheet won't know how to locate the columns to read and write data and your app will stop functioning. Column headers are essential to your app: you need column headers for each column in which you want to store data.
AppSheet reads the first few rows of your spreadsheet to locate your column headers. Normally your column headers should be the first row of your spreadsheet, but AppSheet is capable of finding your headers if they're anywhere near the top of your spreadsheet.
Before you add a new table, it's a good idea to open your worksheet and make the header row bold, which helps AppSheet locate it.
Rows: Every time you add new data, a new row will be added to the spreadsheet.
Adding Multiple Tables
To add multiple tables after you have created your app, go to the Editor > Data > Tables and add a new table:
If you're already using a table source that has multiple worksheets or tabs, AppSheet will suggest some unused worksheets from which to create a new table.
If you don't see the worksheet you want, you can select an existing table source from the drop-down menu. From there, you can choose an unused worksheet and create a new table.
If you want to add an entirely new table source--a new spreadsheet, for example--just select "Browse for new source" from the table source drop-down menu.
AppSheet will ask you to select a new file; if you have multiple data sources, it will prompt you to select a new data source. You may select the same spreadsheet, or a different one from a different data source.
When you add a new table--or when you're editing an existing table--you can choose how data is accessed in the app. You can allow people to Add, Update, and Delete rows, or any combination of the three.
Tips for Tables
AppSheet uniquely identifies a row by the value in one of its columns. That's where the concept of keys becomes essential in an AppSheet app.
Using keys as a way to locate rows in the spreadsheet also allows for multiple users adding data at the same time. AppSheet will "serialize" the data going back to the spreadsheet from the app, letting the last person to write in a cell "win".