24/10/2012 Cc quy tc ti u ha cu lnh truy v n trong SQL
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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
