JOINs suna haɗa layuka daga tebloli da yawa bisa ga ginshiƙi mai alaƙa — mahimman aikin don buƙatar bayyanar bayanan da ke yaɗa tebloli. Nau'in haɗe nau'i ya ƙayyade waɗanne layuka za a ajiye idan babu daidai.
users.name, orders.total
users
orders users.id orders.user_id;
Șecewa ON ta ƙayyade yadda tebloli ke alaƙa (daidaitawa na maɓalli na gida da maɓalli na mafi girma). Nau'in haɗe yana ƙula da abin da ya faruwa ga layuka da ba su daidai ba.
INNER JOIN → only rows that MATCH in BOTH tables (the intersection)
users WITH orders only — users with no orders are excluded
LEFT JOIN → ALL rows from the LEFT table + matches from the right (NULL if no match)
ALL users, with their orders (or NULL for users with no orders)
RIGHT JOIN → ALL rows from the RIGHT table + matches from the left (NULL if no match)
ALL orders, with their user (mirror of LEFT)
FULL JOIN → ALL rows from BOTH tables (matched where possible, NULL where not)
-- INNER — only users who have orders
SELECT u.name, o.total FROM users u INNER JOIN orders o ON u.id = o.user_id;
-- LEFT — ALL users, even those with no orders (o.total is NULL for them)
SELECT u.name, o.total FROM users u LEFT JOIN orders o ON u.id = o.user_id;
-- LEFT JOIN + IS NULL → users who have NEVER ordered
SELECT u.name
FROM users u
LEFT JOIN orders o ON u.id = o.user_id
WHERE o.id IS NULL; -- no matching order → o.id is NULL
LEFT JOIN + IS NULL alƙali yana neman layuka a cikin tebol gida tare da babu layukar da ta daidai a cikin wata — hanya mai ƙiga da amfani sosai.
INNER → A ∩ B (matches only)
LEFT → all A + matching B
RIGHT → all B + matching A
FULL → all A + all B
JOINs sun kasance ainihi ga bayanan tebloli da alaƙa — bayanan an fili ɓarewa a tebloli masu alaƙa (masu amfani, oda, kayan arziki), kuma JOINs shine yadda za a haɗa waɗannan bayanan da alaƙa a buƙatun, don haka fahimta su ya zama mahimmi sabili da ko wane aiki mara sauƙi na bayanan.
Fahimta nau'iyoyin haɗe hudu da abin da suke yi da layuka marasa daidai shine ƙwararren ƙwararren: INNER JOIN (layuka marasa daidai kawai — mafi gida), LEFT JOIN (duk layuka daga tebol dabam, tare da NULLs don marasa daidai — mahimmi idan kana buƙatar duk bayanan ko dai akwai daidai), RIGHT JOIN (madubensa), da FULL JOIN (duk layuka daga tebloli biyu). /* Zabar nau'in haɗe daidai ya ƙayyade sakamakon ka — amfani da INNER lokacin da keka niyya LEFT a hankali ɗaga layuka (bugi gama gari), don haka fahimta bambanci mahimmi ne sabili ga daidai.
LEFT JOIN + IS NULL alƙali (neman layuka tare da babu daidai a wata tebol — kamar masu amfani waɗanda ba su budatawa ba) muhimmin alƙali ne, alƙali gari dai sani.
Domin bayanan tebloli tare da alaƙa an fili a tebloli da JOINs shine hanyar mafi girma don buƙatar, kuma nau'in haɗe ya sa tasiri mai mahimmanci akan waɗanne layuka suka bayyana a sakamakon, sarrafa JOINs — nau'iyoyin hudu, halayensu tare da marasa daidai, da alƙali kamar anti-joins — ainihi, sanina da aka amfani gari sabili da SQL kuma ɗaya daga cikin ainihi mahimman da aka tabaita bayanan hanyoyin.