Rails PostgreSQL wrong decimal to numeric convertion after migration

rubyonrails-talk
1

After running a migration I noticed that rails is changing the specified decimal data type in PostgreSQL. Is there a reason for that?

According to this post:

I found that there is a slight difference between decimal type and numeric type:

NUMERIC must be exactly as precise as it is defined — so if you define 4 decimal places, the DB must always store 4 decimal places.

DECIMAL must be at least as precise as it is defined. This means that the database can actually store more digits then specified (due to the behind-the-scenes storage having space for extra digits). This means the database might store 1.00005 instead of 1.0000, affecting future calculations.

class CreateBooks < ActiveRecord::Migration   def change     create_table :books, id: :uuid do |t|       t.decimal :price       t.string :title       t.timestamps     end   end end

After running this migration, the column price is of numeric type instead of decimal.

Any feedback is appreciated

Rod

2

Via: PostgreSQL: Documentation: 9.4: Numeric Types

"The types decimal and numeric are equivalent. Both types are part of the SQL standard."

HTH,

3

OK, but if they are the same there would be no need for 2 different types under PostgreSQL database. According to the post link provided, decimal is more flexible allowing to store less decimal as opposed to numeric which requires all decimal places to be filled in. This means that using decimal I could stored the numbers 12345.12345 as well as 12345.12. In the other hand, numeric would only accept 12345.12345 or 12345.12000 if I understood it right.

4

So you prefer to believe a 5-year-old SO post rather than actual product documentation?

Up to you. Regardless, while I read it as numeric and decimal being the same thing, you can test that theory yourself. Here's one way:

testdb=# create table things ( name varchar(255), price decimal ); testdb=# \dS things             Table "public.things" Column | Type | Modifiers

5

Thank. Don´t need to say anything else. Indeed it is not rails fault.

PostgreSQL 9.3.5 on x86_64-unknown-linux-gnu, compiled by gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3, 64-bit

Hassan Schroeder wrote in post #1167348: