Try using the sqlite shell program and the explain feature. You will see that each column fetched requires an additional opcode to do the fetching and an additional register to hold the result, all of this on top of requiring SQLite to decode all of these fields without you ever intending to use the results of all this CPU labor.
-----Ursprüngliche Nachricht----- Von: sqlite-users [mailto:sqlite-users-boun...@mailinglists.sqlite.org] Im Auftrag von Jens Alfke Gesendet: Samstag, 15. Oktober 2016 20:01 An: SQLite mailing list <sqlite-users@mailinglists.sqlite.org> Betreff: [sqlite] Any performance penalty for SELECTing more columns? (C API) In a simple SELECT query of a single table, using the C API, is there any difference in performance for requesting more or fewer columns of the table in the result? Or is the performance penalty only incurred when actually reading the column values? For example, lets say a table has 26 columns, some of which can be large strings/blobs. I prepare two statements: SELECT a FROM mytable WHERE … SELECT a,b,c,d,…,z FROM mytable WHERE … If I run both of those queries, but in my loop I only read the value of ‘a’, by calling sqlite3_column_text(stmt, 0), is there any difference in speed? I am guessing that there isn’t a difference. (I could run tests, but I don’t want to be dependent on a detail that might change.) If so, this will make it easier to create my queries, since I won’t have to fine-tune their column sets based on what columns I need in each different use case. —Jens _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users ___________________________________________ Gunter Hick Software Engineer Scientific Games International GmbH FN 157284 a, HG Wien Klitschgasse 2-4, A-1130 Vienna, Austria Tel: +43 1 80100 0 E-Mail: h...@scigames.at This communication (including any attachments) is intended for the use of the intended recipient(s) only and may contain information that is confidential, privileged or legally protected. Any unauthorized use or dissemination of this communication is strictly prohibited. If you have received this communication in error, please immediately notify the sender by return e-mail message and delete all copies of the original communication. Thank you for your cooperation. _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
