Which is faster/best? SELECT * or SELECT column1, colum2, column3, etc

Question

I\'ve heard that SELECT * is generally bad practice to use when writing SQL commands because it is more efficient to SELECT columns you specificall

Answer 1

SELECT * is a bad practice even if the query is not sent over a network.

1. Selecting more data than you need makes the query less efficient - the server has to read and transfer extra data, so it takes time and creates unnecessary load on the system (not only the network, as others mentioned, but also disk, CPU etc.). Additionally, the server is unable to optimize the query as well as it might (for example, use covering index for the query).
2. After some time your table structure might change, so SELECT * will return a different set of columns. So, your application might get a dataset of unexpected structure and break somewhere downstream. Explicitly stating the columns guarantees that you either get a dataset of known structure, or get a clear error on the database level (like 'column not found').

Of course, all this doesn't matter much for a small and simple system.