SQL DISTINCT clause yog siv los tshem tawm cov kab sib npaug ntawm qhov tshwm sim. Cov lus tseem ceeb sib txawv yog siv nrog xaiv lo lus tseem ceeb hauv kev sib txuas. Nws yog qhov pab tau thaum peb tsis txhob muab cov nqi sib npaug tam sim no nyob rau hauv cov kab / rooj. … DISTINCT tshem tawm cov ntaub ntawv sib npaug ntawm lub rooj.
Lub hom phiaj ntawm cov lus sib txawv yog dab tsi?
The SQL DISTINCT clause yog siv kom tshem tawm cov duplicates los ntawm cov txiaj ntsig ntawm SELECT nqe lus.
Vim li cas peb yuav tsum tsis txhob siv qhov txawv hauv SQL?
Qhov no yog vim li cas kuv ntshai siv "qhov txawv" - lub rooj spraddr yuav suav nrog cov kab ntxiv uas koj yuav tsum siv lim tawm cov ntaub ntawv, thiab " txawv" yuav yog zais qhov ntawd. Tsis tas li ntawd, koj tuaj yeem tsim cov txiaj ntsig loj heev uas yuav tsum tau lim los ntawm "qhov txawv", uas tuaj yeem ua rau muaj teeb meem kev ua haujlwm.
Vim li cas cov lus txib sib txawv siv hauv MySQL?
The MySQL DISTINCT clause yog siv los tshem tawm cov duplicates ntawm qhov tshwm sim. DISTINCT clause tsuas yog siv tau nrog SELECT nqe lus xwb.
Dab tsi tuaj yeem siv hloov qhov sib txawv hauv SQL?
Hauv qab no yog lwm txoj kev daws teeb meem:
- Tshem tawm Duplicates Siv Row_Number. NROG CTE (Col1, Col2, Col3, DuplicateCount) AS (SELECT Col1, Col2, Col3, ROW_NUMBER OVER(PARTITION BY Col1, Col2, Col3 ORDER BY Col1) AS DuplicateCount FROM MyTable) SELECTlos ntawm CTE Qhov twg DuplicateCount=1.
- Tshem tawmDuplicates siv pab pawg By.
