Muaj ob hom kev koom nrog hauv DBMS 1) Sab Hauv Koom 2) Kev Koom Tes sab nraud. Ib qho kev koom nrog sab hauv yog qhov kev siv dav siv los koom ua ke thiab tuaj yeem suav tias yog hom kev sib koom ua ke. Inner Join tau muab faib ua 3 subtypes: 1) Theta koom 2) Natural koom 3) EQUI koom.
Dab tsi koom nrog hauv Rdbms?
Nyob rau hauv DBMS, ib daim ntawv koom ua ke yog feem ntau yog siv los ua ke ob lub rooj raws li ib qho kev qhia tshwj xeeb ntawm lawv. Yog hais tias peb tham nyob rau hauv cov nqe lus ntawm Relational algebra, nws yog cov khoom cartesian ntawm ob lub rooj ua raws li kev xaiv ua haujlwm.
Muaj pes tsawg hom kev koom nrog hauv Rdbms?
Ib qho kev koom nrog hauv SQL - sib raug rau kev koom tes hauv kev sib raug zoo algebra - sib txuas cov kab los ntawm ib lossis ntau lub rooj rau hauv lub rooj tshiab. ANSI-tus qauv SQL qhia meej tsib homntawm Kev Koom Tes: Sab Hauv, Sab Nraud Sab Nraud, Sab Nraud Sab Nraud, FULL OUTER thiab CROSS.
hom kev koom nrog yog dab tsi?
Type of joins
- Cross koom. Ib qho kev sib koom ua ke rov qab txhua qhov ua tau ua ke ntawm kab ntawm ob lub rooj (tseem hu ua Cartesian khoom).
- Koom/sib koom nrog. Ib qho kev koom nrog sab hauv, tseem hu ua kev koom ua ke yooj yim, rov qab kab los ntawm cov rooj sib txuas uas muaj cov kab sib txuam. …
- Sab laug sab koom / sab laug koom.
- Txoj kev sib koom / sab xis koom.
- tag nrho sab nraud koom.
Dab tsi yog Koom nrog thiab nws hom hauv DBMS?
Kev Koom Tes yog tseem ceeb yog siv los ua ke muaj feem cuam tshuam los ntawm ob lossis ntau qhov kev sib raug zoo rau hauv ib hom. … Hauv cov lus yooj yooj yim, nws yog siv los muab cov ntaub ntawv los yog kab los ntawm ob lossis ntau lub rooj raws li paub cov yam ntxwv uas muaj txiaj ntsig zoo sib xws.
