Query speed based on order of columns

Question

Does the order of the column types in your database have any affect on the query time?

For example, would a table with mixed ordering (INT, TEXT, VARCHAR, INT, TEXT) be

Answer 1

In PostgreSQL, you will get an advantage if you put fixed-width columns first because that access path is specially optimized. So (INT, INT, VARCHAR, TEXT, TEXT) will be fastest (the relative order of VARCHAR and TEXT doesn't matter).

Additionally, you can save space, which can translate to more throughput and performance, if you manage the alignment requirements of the types correctly. For example, (INT, BOOL, INT, BOOL) will require 13 bytes of space because the third column has to be aligned at a 4-byte boundary, and so there will be 3 bytes of space wasted between the second and the third column. Better here would be (INT, INT, BOOL, BOOL). (Whatever comes after this row will probably also require alignment of at least 4 bytes, so you will waste 2 bytes at the end.)