Video: Vim li cas SQL Server xav tau CTE?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Common Table Expressions los yog CTE cov luv luv yog siv nyob rau hauv SQL Server kom yooj yim rau kev sib koom ua ke thiab cov lus nug, thiab muab ib txoj hauv kev los nug cov ntaub ntawv hierarchical xws li daim ntawv qhia txog kev ua haujlwm.
Yog li ntawd, vim li cas peb thiaj xav tau CTE hauv SQL Server?
Vim li cas thiaj siv a CTE Hauv SQL ntawv , peb yuav siv sub-queries koom nrog cov ntaub ntawv los yog lim cov ntaub ntawv los ntawm ib tug sub-query. Thaum twg peb xa tib cov ntaub ntawv lossis koom nrog tib cov ntaub ntawv siv cov lus nug, cov cai tswj xyuas yuav nyuaj. A CTE ua kom zoo nyeem ntawv thiab kev saib xyuas yooj yim dua.
Tom qab, lo lus nug yog, CTE yog dab tsi hauv SQL Server thiab nws siv? SQL Server CTE Cov hauv paus. Taw qhia hauv SQL Server 2005, cov lus qhia dav dav ( CTE ) yog lub npe teev npe ib ntus uas koj tuaj yeem siv hauv SELECT, INSERT, UPDATE, lossis DELETE nqe lus. Koj tuaj yeem ua tau siv a CTE hauv daim ntawv CREATE VIEW, uas yog ib feem ntawm tus saib SELECT nug.
Ib sab saum toj no, dab tsi yog qhov zoo ntawm kev siv CTE hauv SQL Server?
CTE siv los hloov qhov saib uas khaws cov metadata. CTEs pab txhim kho kev nyeem ntawv ntawm cov cai yam tsis muaj kev cuam tshuam kev ua haujlwm. Lawv pab txhim kho kev ruaj ntseg ntawm cov cai yam tsis muaj kev cuam tshuam kev ua haujlwm. Lawv sau cov code recursive hauv T- SQL ntawv yooj yim dua li yav dhau los SQL Server cov qauv.
Kuv tuaj yeem txhim kho kuv qhov kev ua tau zoo CTE li cas?
Koj muaj ob txoj kev xaiv: lo qhov tshwm sim ntawm koj thawj zaug CTE rau hauv #temp table. Ntxiv cov lej suav rau koj lub rooj hauv paus.
3 Teb
- Koj koom nrog hauv kev lag luam CTE.
- Koj rau kev lag luam hauv searchResults.
- Tag nrho cov COUNT subqueries hauv koj qhov kev xaiv zaum kawg los ntawm kev tshawb nrhiav.
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