Thaum ua haujlwm hauv Oracle, koj yuav pom tias qee qhov ntawm koj cov ntaub ntawv muaj qhov theej tawm. Koj tuaj yeem tshem tawm cov kab sib tshooj no los ntawm kev txheeb xyuas lawv thiab siv nws RowID, lossis kab lus chaw nyob. Ua ntej koj pib, koj yuav tsum tsim lub rooj thaub qab yog tias koj xav tau siv lawv tom qab koj tau tshem cov ntaub ntawv.
Cov kauj ruam
Txoj Kev 1 ntawm 4: Txheeb xyuas koj li theej tawm
Kauj Ruam 1. Txheeb xyuas qhov theej tawm
Hauv qhov no, txheeb xyuas qhov piv txwv sib piv, "Alan." Nco ntsoov tias cov ntaub ntawv koj tab tom sim muab rho tawm yog qhov sib thooj los ntawm kev nkag mus rau SQL hauv qab no.
Kauj Ruam 2. Txheeb los ntawm kab ntawv npe "Npe
"Hauv qhov piv txwv ntawm kab ntawv npe" Npe, "koj yuav hloov" column_name "nrog Cov Npe.
Kauj Ruam 3. Txheeb cais los ntawm lwm kab
Yog tias koj tau sim txheeb xyuas qhov sib thooj los ntawm kab sib txawv, piv txwv li hnub nyoog ntawm Alan ntau dua li nws lub npe, koj yuav nkag mus "Hnub Nyoog" nyob rau qhov chaw ntawm "column_name" thiab ntxiv rau.
xaiv column_name, suav (column_name) los ntawm pawg pawg los ntawm column_name muaj suav (column_name)> 1;
Txoj Kev 2 ntawm 4: Rho Tawm Ib Leeg
Kauj Ruam 1. Xaiv "npe los ntawm cov npe
"Tom qab" SQL, "uas sawv cev rau Standard Query Language, sau" xaiv lub npe los ntawm cov npe."
Kauj Ruam 2. Rho tawm txhua kab uas muaj lub npe theej tawm
Tom qab "SQL," sau "rho tawm ntawm cov npe qhov twg lub npe = 'Alan';" Nco ntsoov tias kev nqis peev tseem ceeb ntawm no, yog li qhov no yuav tshem tawm txhua kab uas muaj npe "Alan." Tom qab "SQL," nkag mus "cog lus."
Kauj Ruam 3. Xauj kab uas tsis muaj qhov theej tawm
Tam sim no koj tau tshem tag nrho kab nrog piv txwv lub npe "Alan," koj tuaj yeem ntxig ib qho rov qab los ntawm kev nkag mus "ntxig rau hauv lub npe qhov tseem ceeb ('Alan');" Tom qab "SQL," sau "cog lus" los tsim koj kab tshiab.
Kauj Ruam 4. Saib koj daim ntawv teev npe tshiab
Thaum koj tau ua tiav cov theem saum toj no, koj tuaj yeem tshawb xyuas kom paub tseeb tias koj tsis muaj cov ntaub ntawv theej tawm lawm los ntawm kev nkag mus "xaiv * los ntawm cov npe."
SQL> xaiv lub npe los ntawm cov npe; NPE ------------------------------ Alan Carrie Tom Alan kab xaiv. SQL> rho tawm ntawm cov npe nyob qhov twg lub npe = 'Alan'; kab raug tshem tawm SQL> cog lus; Ua tiav. SQL> ntxig rau lub npe qhov tseem ceeb ('Alan'); kab tsim. SQL> cog lus; Ua tiav. SQL> xaiv * los ntawm cov npe; Npe ------------------------------ Alan Carrie Tom kab xaiv.
Txoj Kev 3 ntawm 4: Rho Tawm Ntau Yam Luam
Kauj Ruam 1. Xaiv RowID koj xav rho tawm
Tom qab "SQL," sau "xaiv rowid, npe los ntawm cov npe;"
Kauj ruam 2. Rho tawm qhov theej tawm
Tom qab "SQL," sau "rho tawm ntawm cov npe nyob qhov twg rowid> (xaiv min (rowid) los ntawm cov npe b qhov twg b.name = a.name); kom rho tawm cov ntaub ntawv theej tawm.
Kauj Ruam 3. Txheeb xyuas qhov sib thooj
Tom qab koj tau ua tiav cov lus saum toj no, cov lus txib txheeb xyuas seb koj puas tseem muaj cov ntaub ntawv theej tawm los ntawm kev nkag mus "xaiv kab, npe los ntawm cov npe;" thiab tom qab ntawd "cog lus."
SQL> xaiv rowid, npe los ntawm cov npe; ROWID NPE ------------------------------- AABJnsAAGAAAdfOAAA Alan AABJnsAAGAAAdfOAAB Alan AABJnsAAGAAAdfOAAC Carrie AABJnsAAGAAAdfOAAD Tom AABJnsAAGAAAdfOAAF Alan kab xaiv. SQL> rho tawm ntawm cov npe nyob qhov twg rowid> (xaiv min (rowid) los ntawm cov npe b qhov twg b.name = a.name); kab raug tshem tawm SQL> xaiv rowid, npe los ntawm cov npe; ROWID NPE ------------------------------- AABJnsAAGAAAdfOAAA Alan AABJnsAAGAAAdfOAAC Carrie AABJnsAAGAAAdfOAAD Tom kab xaiv. SQL> cog lus; Ua tiav.
Txoj Kev 4 ntawm 4: Tshem Rows nrog Kab
Kauj Ruam 1. Xaiv koj kab
Tom qab "SQL," sau "xaiv * los ntawm cov npe;" kom pom koj kab.
Kauj Ruam 2. Rho tawm kab sib tshooj los ntawm kev txheeb xyuas lawv kab ntawv
Tom qab "SQL '" sau "rho tawm ntawm cov npe nyob qhov twg rowid> (xaiv min (rowid) los ntawm cov npe b qhov twg b.name = a.name thiab b.age = a.age);" kom rho tawm cov ntaub ntawv theej tawm.
Kauj Ruam 3. Txheeb xyuas qhov sib thooj
Thaum koj tau ua tiav cov theem saum toj no, sau "xaiv * los ntawm cov npe;" thiab tom qab ntawd "ua txhaum" txhawm rau txheeb xyuas tias koj tau tshem cov ntaub ntawv theej tawm ua tiav.
SQL> xaiv * los ntawm cov npe; Lub Npe Hnub Nyoog ------------------------------ ---------------------- Alan 50 Carrie 51 Tom 52 Alan 50 kab xaiv. SQL> rho tawm ntawm cov npe nyob qhov twg rowid> (xaiv min (rowid) los ntawm cov npe b qhov twg b.name = a.name thiab b.age = a.age); kab deleted. SQL> xaiv * los ntawm cov npe; NPE AGE ------------------------------ ---------------------- Alan 50 Carrie 51 Tom 52 kab ntawv xaiv. SQL> cog lus; Ua tiav.
Lus ceeb toom
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Tsim lub rooj thaub qab hauv koj tus kheej kev kos npe nkag uas koj tuaj yeem siv los qhia dab tsi nyob ntawd ua ntej muaj kev tshem tawm tshwm sim (yog tias muaj lus nug).
SQL> tsim cov lus alan.names_backup raws li xaiv * los ntawm cov npe; Rooj tsim.
