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select.md

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Jahongir Temirov

Select

Jadvaldagi ma'lumotlarni so'rash uchun siz SELECT bayonotdan foydalanasiz. Quyidagilar SELECT bayonotning eng asosiy shaklini ko'rsatadi:

SELECT select_list FROM schema_name.table_name;

Ushbu sintaksisda:

  • Birinchidan, banddagi ma'lumotlarni so'ramoqchi bo'lgan vergul bilan ajratilgan ustunlar ro'yxatini belgilang.
  • Ikkinchidan, manba jadvalini va uning sxema nomini FROM bandda belgilang.

Bayonotni qayta ishlashda SELECT, SQL Server SELECT so'rovda birinchi bo'lib paydo bo'lishiga qaramay, avval FROM, keyin esa SELECT qayta ishlaydi.

SELECT id,name FROM Students;

SELECT ishlashi

SELECT da "*" yordamida barcha column belgilash mumkin. Lekin bu har doim ham yaxshimas. Ba'zi xollarda dasturni sekinlashtiradi, keraksiz ma'lumotlarni oladi.

SELECT tartibi

  • FROM
  • ON
  • JOIN
  • WHERE
  • GROUP BY
  • WITH CUBE or WITH ROLLUP
  • HAVING
  • SELECT
  • DISTINCT
  • ORDER BY
  • TOP

Misollar:

SELECT *  FROM DimEmployee  ORDER BY LastName;
SELECT e.*  FROM DimEmployee AS e ;
SELECT FirstName, LastName, StartDate AS FirstDay  FROM DimEmployee;
SELECT FirstName, LastName, BaseRate, BaseRate * 40 AS GrossPay  FROM DimEmployee ;
SELECT DISTINCT Title  FROM DimEmployee  ORDER BY Title;

DISTINCT turli nomlarni qaytaradi. ORDER BY tartiblaydi.