Joins & Relationships
LEFT & RIGHT JOIN
Including Non-Matching Rows
💡 LEFT JOIN, EK, "PRIORITY, LIST" jaisa, hai — LEFT, table, ki, SAARI, rows, RESULT, mein, HONGI, CHAHE, RIGHT, table, mein, MATCH, mile, ya, NA, mile (NULL, se, fill, ho, jaata, hai, agar, match, nahi, milta).
LEFT JOIN, LEFT, table, ki, SAARI, rows, RETURN, karta hai, PLUS, matching, right, table, rows (agar, match, nahi, hai, right, side, ke, columns, NULL, hote, hain). RIGHT JOIN, ULTA, karta hai.
LEFT JOIN, KAAFI, COMMON, hai — jaise, SAARE, users, ko, DIKHANA, CHAHE, unhone, koi, order, place, kiya, ho, YA, na, kiya, ho.
-- Saare users, chahe order ho ya na ho:
SELECT users.name, orders.amount
FROM users
LEFT JOIN orders ON users.id = orders.user_id;
-- Users jinka, order, nahi hai, unke, liye, orders.amount = NULL🌉
LEFT JOIN, EK, "PRIORITY, LIST" jaisa, hai — LEFT, table, ki, SAARI, rows, RESULT, mein, HONGI, CHAHE, RIGHT, table, mein, MATCH, mile, ya, NA, mile (NULL, se, fill, ho, jaata, hai, agar, match, nahi, milta).
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⚡ झट से Recap
- LEFT JOIN = left table ki, saari rows, plus, matching right rows
- Non-matching, rows, ke, liye, right, side, ke, columns, NULL, hote, hain
- Common, pattern, — orphaned, records, dhoondhne, ke, liye
इस page में (2 subtopics)
MySQL, natively, FULL OUTER JOIN, support, NAHI, karta, (unlike, PostgreSQL) — LEFT JOIN, aur, RIGHT JOIN, ko, UNION, se, COMBINE, karके, EK, similar, effect, achieve, kiya, ja, sakta hai.
SELECT * FROM a LEFT JOIN b ON a.id = b.a_id
UNION
SELECT * FROM a RIGHT JOIN b ON a.id = b.a_id;LEFT JOIN + WHERE right.id IS NULL, EK, COMMON, pattern, hai, WOH, rows, dhoondhne, ke, liye, jinka, KOI, MATCH, dusri, table, mein, NAHI, hai — jaise, "products, jo, KABHI, order, nahi, hue".
Tip: Ye, pattern, "anti-join" kehlata, hai — SQL, mein, KOI, DIRECT, "NOT JOIN" syntax, nahi, hai, isliye, ye, workaround, common, hai.