Upload
thai-son
View
59
Download
7
Embed Size (px)
Citation preview
24/10/2012 Cc quy tc ti u ha cu lnh truy v n trong SQL
1/1asp.net.v n/Modules/ASPNETVN.PORTAL.Modules.CMS/Pages/Print.aspx?itemid=244
Cc quy tc ti u ha cu lnh truy vn trong SQL
y l ch c bn rt lu v rt nhiu ri nhng vn phi nhc li bi n vn cc k quan trng hin
nay.
Di y l cc quy tc:
- Bng (table) phi c kha chnh (Primary Key).
- Bng (table) phi c t nht 01 clustered index.- Bng (table) phi c s lng non-clustered index ph hp.
- Non-clustered index phi c to trn cc ct (column) ca bng (table) da vo nhu cu truy vn.
- Da theo s sp xp th t nh sau khi c bt k index c to: a) WHERE clause, b) JOIN clause, c)
ORDER BY clause, d) SELECT clause
- Khng nn dng Views thay cho bng (table) gc.
- Triggers khng nn s dng nu khng cn thit, nn nhp nhng x l t trigger vo trong th tc (stored
procedure).
- G b nhng cu lnh query trc tip v thay bng th tc (stored procedure).- Phi c t nht 30% khng gian a cng trn phn vng cha database.
- Nu c th hy chuyn UDF (user defined function) sang SP (stored procedure) .
- Ch SELECT nhng ct cn thit, khng nn SELECT *.
- G b cc joins t cc bng (table) khng cn thit.
- Hn ch s dng con tr (cursor)- m bo phn cng p ng nhu cu ca h thng.
In trang