DISTINCT yana cire jeri masu ƙididdige daga sakamakon, yana mayar da kawai ƙimomi masu zaman kansu. Ana amfani da shi don samun ɓatattun ƙimomi na ginshiƙi (ko haɗin ginshiƙi) — galibi don neman zazzage masu zaman kansu ko gina jerin baje.
country users;
country, city users;
DISTINCT yana aiki akan dukkan ginshiƙin da aka zaɓa tare — DISTINCT country, city yana mayar da masu zaman kansu haɗe-haɗe, ba ƙasua kasuwa da birni masu zaman kansu daban.
-- count how many UNIQUE countries there are
SELECT COUNT(DISTINCT country) FROM users;
-- vs COUNT(*) which counts all rows (with duplicates)
SELECT COUNT(*) FROM users;
COUNT(DISTINCT column) yana ƙididdige ƙimomi masu zaman kansu — nauyi don "nawa daban-daban X?".
-- find values that appear MORE THAN ONCE (duplicates)
SELECT email, COUNT(*) AS count
FROM users
GROUP BY email
HAVING COUNT(*) > 1; -- groups with more than one row = duplicates
Don nema ɗin kayi (ba kawai cire su), yi amfani da GROUP BY + HAVING COUNT(*) > 1 — wannan yana gano wane ƙimomi ne suke ɗin kayi da sau nawa.
-- these are often equivalent for getting unique values:
SELECT DISTINCT country FROM users;
SELECT country FROM users GROUP BY country;
-- GROUP BY is more flexible (can add aggregates); DISTINCT is simpler for pure deduplication
DISTINCT requires the database to compare/sort rows to find uniques → can be costly
on large datasets. Often a sign you might restructure the query (e.g. a JOIN producing
duplicates that DISTINCT then removes — consider whether the JOIN is the issue).
DISTINCT kuɗi mai amfani ne, siɗi mahimmacin abin SQL don jima da ɗin kayi — samun ƙimomi masu zaman kansu shine buɗe matakin a gida (ƙasua masu zaman kansu don ja-waje, zazzage masu zaman kansu, ƙididdige abubuwa masu zaman kansu), sabili da haka fahimtar sa shine ilimin aiki na yau da kullun.
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