Question

I have a db with many tables. Some tables have unit price column, no tax, gst and such columns. What should i do now? Should i create GST table, HST table and PST table separately. In other words, what is the standard schema of designing the tax table?

Answer 1

You only need one table for tax percentages:

CDN_TAXES

• tax_id (primary key)
• tax_name (GST, HST, PST)
• tax_percentage

Because HST covers both PST and GST, I’d model this as three columns in the PRODUCT/etc table and use a CHECK constraint to enforce that either the HST column be associated, or at least one of PST/GST is associated to the product.

The amount of tax per sale, should be stored in a SALES table. Tax tables in Canada are updated twice a year, and the percentage can change. Which means if you want to reprint a receipt that is accurate, you have to capture the tax amounts at the time of sale.