Count(<name>) needs to extract the <name> field from the record, tallying only those that are NOT NULL.
Count(*) returns the total number of records in the table, with no need to extract a specific field. When looking into efficiency, try using the .explain/explain feature. asql> explain select count(a) from t; addr opcode p1 p2 p3 p4 p5 comment ---- ------------- ---- ---- ---- ------------- -- ------------- ... 4 OpenRead 0 2 1 1 00 t 5 Rewind 0 9 0 00 NULL 6 Column 0 0 3 00 t.a 7 AggStep 0 3 1 count(1) 01 NULL 8 Next 0 6 0 01 NULL 9 Close 0 0 0 00 NULL 10 AggFinal 1 1 0 count(1) 00 NULL 11 Copy 1 4 0 00 NULL 12 ResultRow 4 1 0 00 NULL ... asql> explain select count(*) from t; addr opcode p1 p2 p3 p4 p5 comment ---- ------------- ---- ---- ---- ------------- -- ------------- ... 2 OpenRead 1 2 1 00 NULL 3 Count 1 1 0 00 NULL 4 Close 1 0 0 00 NULL 5 Copy 1 2 0 00 NULL 6 ResultRow 2 1 0 00 NULL ... -----Ursprüngliche Nachricht----- Von: sqlite-users [mailto:sqlite-users-boun...@mailinglists.sqlite.org] Im Auftrag von Cecil Westerhof Gesendet: Dienstag, 05. September 2017 22:22 An: SQLite mailing list <sqlite-users@mailinglists.sqlite.org> Betreff: [EXTERNAL] [sqlite] Is there a performance difference between COUNT(*) and COUNT(name) I want to know the number of teas I have in stock. For this I use: SELECT COUNT(Tea) FROM teaInStock Tea cannot be NULL, so this is the same as: SELECT COUNT(*) FROM teaInStock But I find the first more clear. I almost always see the second variant. Is this because it is more efficient, or are people just ‘lazy’? -- Cecil Westerhof _______________________________________________ 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
