KUKHALA SQL: kufotokozera, mawu ofanana, zitsanzo

SQL ndi chilankhulidwe chokha chogwiritsira ntchito ndi mafotokozedwe achibale. Ali ndi zida zake zamphamvu zogwiritsira ntchito deta yosungidwa m'mawonekedwe a matebulo.

Mosakayika, kuthekera kwa deta deta pamene tingaphunzire ndi chinthu china ndi chida chimodzi chotere. Mawu a SQL HAVING , pamodzi ndi WHERE clause, amakulolani kufotokozera zitsanzo za zitsanzo za deta zomwe zakhala zikugawidwa kale.

KUKHALA NDI SQL parameter: kufotokoza

Choyamba, tiyenera kukumbukira kuti izi ndizosankha ndipo zimagwiritsidwa ntchito palimodzi ndi GROUP BY parameter. Monga mukukumbukira, GROUP BY imagwiritsidwa ntchito pamene SELECT imagwiritsira ntchito ntchito zonse, ndipo zotsatira za mawerengero awo ziyenera kupezedwa kwa magulu ena. Ngati WHERE ikulolani kuti mupange zosankhidwa musanagwiritse ntchito deta, ndiye kukhala ndi zikhalidwe zokhudzana ndi deta kale m'magulu okha. Kuti timvetse bwino, tiyeni tiwone chitsanzocho ndi chithunzi chomwe chikuwonetsedwa pa chithunzichi pansipa.

Ichi ndi chitsanzo chabwino, ndikupereka ndemanga ya HAVING SQL. Tebulo laperekedwa ndi mndandanda wa mayina ogulitsa, makampani omwe amawabweretsa, ndi zina. Mu funsoli pa ngodya yapamwamba, tikuyesera kupeza zambiri za mayina a malonda omwe kampani iliyonse imabala, pamene tikufuna kutulutsa makampani okha omwe amapanga zoposa 2 maudindo. GROUP BY parameter anapanga magulu atatu ofanana ndi mayina a makampani, chifukwa chiwerengero cha zinthu (mizera) chinkawerengedwa. Koma parameter YAM'MBUYO YOTSATIRA TUMIZANI LINKI SINDIKIZANI ILI MU KOPERANI MAPODIKASITI MITU YA NKHANI Zotsatira zake, timapeza magulu awiri ofanana ndi makampani omwe ali ndi chiwerengero cha mankhwala 5 ndi 3.

Funso likhoza kuchitika chifukwa chogwiritsira ntchito HAVING ngati kuli PAKUTI mu SQL. Ngati tinkakonda WHERE, tiyang'ana pa nambala ya mizere yomwe ili patebulo, osati m'magulu, ndipo chikhalidwe sichingakhale chopanda nzeru panopa. Komabe, nthawi zambiri amakhala pamodzi mu pempho limodzi.

Mu chitsanzo chapamwamba, titha kuona momwe detayi idayikidwira poyamba ndi mayina ogwira ntchito omwe atchulidwa pa WHERE parameter, ndiyeno zotsatira zake zigawidwa mu GROUP BY zimapereka chitsimikizo choonjezera pa kuchuluka kwa malipiro a wogwira ntchito aliyense.

SQL KUCHITA parameter: zitsanzo, mawu ofanana

Tiyeni tione zina mwachinsinsi za HAVING SQL syntax. Kulongosola kwa parameter iyi ndi kophweka. Choyamba, monga taonera kale, chikugwiritsidwa ntchito pokhapokha ndi GROUP BY parameter ndipo imatchulidwa mwamsanga pambuyo pake ndi pamaso pa ORDER BY, ngati pali imodzi mu funso. Zimamveka, popeza HAVING imatanthauzira zikhalidwe za deta yomwe kale igawidwa. Chachiwiri, panthawiyi, mungagwiritse ntchito ntchito zonse ndi masamba omwe atchulidwa mu GROUP BY parameter. Zonsezi mu parameter iyi zanenedwa ndendende mofanana ndi momwe zilili PAKATI.

Kutsiliza

Monga momwe mukuonera, palibe chovuta pakati apa. Zisemphana zimagwiritsidwa ntchito mofanana ndi WHERE. Ndikofunika kumvetsetsa kuti WHERE imagwiritsidwa ntchito potsata deta yonse yosankhidwa, ndipo HAVING imangogwirizana ndi magulu otchulidwa mu GROUP BY parameter. Tinapereka ndondomeko yambiri ya Kukhala ndi SQL, yomwe ndi yokwanira kuti tigwire bwino ntchitoyi.