If I have mySQL table with 10 fields and I only need the to retrieve values of the some fields, is it advisable to use
SELECT field1, field2, field3 FROM...
rather than
SELECT * FROM...
I mean does it help retrieval / script execution faster if Im using [SELECT field1, field2, field3....]
Yes, if you only want a small selection of fields in a table, it is better to select them rather than pull all the fields back. The difference is not huge but aiming for every optimisation, it may help.
If you have a table with 20 or so fields and want 18 of them, that is where it might be easier/neater to just do a * to get them all.
EDIT
Further information can be found on this question.
yes, you should query only those fields that you need, as not needed fields will have take up network resourse(transporting from db server to backend server) and memory.
Yes, you should always use the SELECT field1, field2, field3... form according to some.
The * is ambiguous and I see the point that just automatically selecting every column from a table is lazy although I'm guilty of using it regularly.
From an optimisation point-of-view you should select only the fields you are planning to use also. It may make debugging clearer if you know explicitly what data is being retrieved.
If You Query a table with 6800 records having 23 Columns
With * it took Average 0.0009 Sec in returning records
And same Query with 5 Columns took average 0.0005 Sec
Tested on Dual Core Machine 2GB RAM , Windows 7 and Phpmyadmin
Conclusion
It's always recommended to use required fields despite of * where speed is on priority
