Storing FTSE stock data I want to store stock data from the FTSE 100 every 10 seconds but am confused how I should set up my tables.

I need to save the price, increase and % increase as well as some way of identifying which stock is which. 

Should I have one massive table with 300+ columns. (3 for each stock)?

Separate tables per stock or something else? 

I will be querying the data using PHP and displaying it on a website.
What I would do is to create a table with the stock_id (that can be the alphanumeric code or a integer), the timestamp of the measurement and the current value. That is your entry data, 3 columns. 

From that point you can add columns for calculations (the difference absolute or percent) with the previous value. Having all in the same table will simplify the model and ease your queries. Try to create a date (not timestamp) column and create a partition by it. It may lighten a bit the access to the table as long as you set it in your queries.