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Which is faster/best? SELECT * or SELECT column1, colum2, column3, etc.
Is it bad practice to use Select * ?
I was going through some old code and saw some 'SELECT *' statements. My previous coworker had told me Select * was bad practice, but I couldn't really see the reason why (unless of course I only needed to return a few fields). But for full 'detail retrieves' (Get by Id type queries) Select * seems right.
Yes, it is deemed bad practice.
It is better to specify an explicit column list, especially if the table contains many columns and you only really need some of them.
Even if you need to select all columns it is still better to specify them rather then use 'select *'
If any schema changes occur (extra columns are added), these will be caught by your application. This might be undesirable, say, if you bind a grid dynamically to a DataTable. Also it incurs more overhead on network communications.
Even if you are selecting all columns as of today, define the columns by name - its readable and explicit. Any additional columns will then not cause any problems with your code.
It's bad practice.
If your schema changes down the road, the calling application may get more fields than it knows what to do with.
Also, you are getting more info than you need, which affects performance.
Also also, it implies you don't know what the columns are.
Using SELECT * is bad practice for two reasons:
Yes, Select * is a bad practice. For one, it is not clear to other developers which columns you really are using. Are you actually using all of them? What happens when you add columns are you using those too? That makes it much more difficult to refactor column names should that need arise. Second, there are some instances where some database systems will remember which columns existed at the time you created an object. For example, if you create a stored procedure with Select *, it will bake in the columns that exist in the table at the time it is compiled. If the table changes, it make not reflect those changes in the stored procedure. There really isn't any reason to use Select * beyond laziness.
When you use SELECT *, you choose to trade immediate productivity (writing a query faster) for potential maintenance productivity (should your underlying query change and thus break dependent code/queries). The "bad-ness" of the practice is a risk management activity.
Select * retorna todos los campos de una tabla, por lo que en ambientes empresariales no es buena idea, ya que se requiere procesos rapidos y eficientes, esto ayuda a los servidores liberandolos de trabajo innecesario