{"id":36639,"date":"2025-12-21T00:30:29","date_gmt":"2025-12-20T21:30:29","guid":{"rendered":"https:\/\/fatihsoysal.com\/blog\/sqlde-joinler-alt-sorgular-ve-gelismis-sorgulama-teknikleri-derinlemesine-bir-bakis\/"},"modified":"2025-12-21T00:30:29","modified_gmt":"2025-12-20T21:30:29","slug":"sqlde-joinler-alt-sorgular-ve-gelismis-sorgulama-teknikleri-derinlemesine-bir-bakis","status":"publish","type":"post","link":"https:\/\/fatihsoysal.com\/blog\/sqlde-joinler-alt-sorgular-ve-gelismis-sorgulama-teknikleri-derinlemesine-bir-bakis\/","title":{"rendered":"SQL’de JOIN’ler, Alt Sorgular ve Geli\u015fmi\u015f Sorgulama Teknikleri: Derinlemesine Bir Bak\u0131\u015f"},"content":{"rendered":"

SQL’de JOIN’ler, Alt Sorgular ve Geli\u015fmi\u015f Sorgulama Teknikleri: Derinlemesine Bir Bak\u0131\u015f<\/h2>\n

Veritabanlar\u0131, modern uygulamalar\u0131n ve i\u015f s\u00fcre\u00e7lerinin temelini olu\u015fturur. Bu veritabanlar\u0131ndan anlaml\u0131 bilgi \u00e7\u0131karman\u0131n en g\u00fc\u00e7l\u00fc yolu ise SQL (Yap\u0131sal Sorgu Dili) kullanmakt\u0131r. \u00d6zellikle b\u00fcy\u00fck ve karma\u015f\u0131k veri k\u00fcmeleriyle \u00e7al\u0131\u015f\u0131rken, basit SELECT<\/code> ifadelerinin \u00f6tesine ge\u00e7mek ve verileri birle\u015ftirmek, filtrelemek ve d\u00f6n\u00fc\u015ft\u00fcrmek i\u00e7in geli\u015fmi\u015f tekniklere ihtiya\u00e7 duyar\u0131z. Bu makalede, SQL’in temel ta\u015flar\u0131ndan olan JOIN operasyonlar\u0131n\u0131, alt sorgular\u0131n g\u00fcc\u00fcn\u00fc ve verimlili\u011fi art\u0131ran ileri seviye sorgulama tekniklerini detayl\u0131 bir \u015fekilde inceleyece\u011fiz. Amac\u0131m\u0131z, veritaban\u0131 uzmanlar\u0131n\u0131n ve geli\u015ftiricilerin, daha karma\u015f\u0131k ve performansl\u0131 sorgular yazma becerilerini geli\u015ftirmelerine yard\u0131mc\u0131 olmakt\u0131r.<\/p>\n

JOIN Operasyonlar\u0131n\u0131 Anlamak: Verileri Birle\u015ftirmenin Temelleri<\/h2>\n

Veritabanlar\u0131 genellikle birden fazla tabloya ayr\u0131lm\u0131\u015f verileri saklar. Bu tablolar aras\u0131ndaki ili\u015fkileri kullanarak anlaml\u0131 sonu\u00e7lar elde etmek i\u00e7in JOIN operasyonlar\u0131 vazge\u00e7ilmezdir. JOIN’ler, bir veya daha fazla tablodaki sat\u0131rlar\u0131, aralar\u0131ndaki ortak s\u00fctunlara (ili\u015fkilere) g\u00f6re birle\u015ftirir.<\/p>\n

INNER JOIN: Ortak Kay\u0131tlar\u0131 Birle\u015ftirme<\/h3>\n

INNER JOIN<\/code>, iki tablonun e\u015fle\u015fen kay\u0131tlar\u0131n\u0131 d\u00f6nd\u00fcr\u00fcr. E\u011fer iki tabloda da e\u015fle\u015fen bir kay\u0131t yoksa, o kay\u0131t sonu\u00e7 k\u00fcmesinde yer almaz. Bu, en s\u0131k kullan\u0131lan JOIN t\u00fcr\u00fcd\u00fcr ve tablolar aras\u0131ndaki birebir veya bire\u00e7ok ili\u015fkileri sorgulamak i\u00e7in idealdir.<\/p>\n

SELECT\n    Musteriler.MusteriAd,\n    Siparisler.SiparisTarihi,\n    Siparisler.ToplamTutar\nFROM\n    Musteriler\nINNER JOIN\n    Siparisler ON Musteriler.MusteriID = Siparisler.MusteriID;\n<\/pre>\n
<\/code><\/p>\n
OUTER JOIN'ler: T\u00fcm Kay\u0131tlar\u0131 Kapsama<\/h3>\n
OUTER JOIN<\/code>'ler, e\u015fle\u015fen kay\u0131tlar\u0131n yan\u0131 s\u0131ra, bir veya her iki tablodaki e\u015fle\u015fmeyen kay\u0131tlar\u0131 da d\u00f6nd\u00fcr\u00fcr. E\u015fle\u015fmeyen tarafta, ilgili s\u00fctunlar NULL<\/code> olarak g\u00f6r\u00fcn\u00fcr.<\/p>\n
LEFT JOIN (LEFT OUTER JOIN): Sol Tablodaki T\u00fcm Kay\u0131tlar<\/h4>\n
LEFT JOIN<\/code>, sol tablodaki t\u00fcm kay\u0131tlar\u0131 ve sa\u011f tabloda e\u015fle\u015fen kay\u0131tlar\u0131 d\u00f6nd\u00fcr\u00fcr. Sa\u011f tabloda e\u015fle\u015fme yoksa, sa\u011f tablonun s\u00fctunlar\u0131 i\u00e7in NULL<\/code> de\u011ferler g\u00f6sterilir.<\/p>\n
SELECT\n    Musteriler.MusteriAd,\n    Siparisler.SiparisTarihi\nFROM\n    Musteriler\nLEFT JOIN\n    Siparisler ON Musteriler.MusteriID = Siparisler.MusteriID;\n<\/pre>\n
<\/code><\/p>\n
RIGHT JOIN (RIGHT OUTER JOIN): Sa\u011f Tablodaki T\u00fcm Kay\u0131tlar<\/h4>\n
RIGHT JOIN<\/code>, sol tablonun tam tersidir. Sa\u011f tablodaki t\u00fcm kay\u0131tlar\u0131 ve sol tabloda e\u015fle\u015fen kay\u0131tlar\u0131 d\u00f6nd\u00fcr\u00fcr. Sol tabloda e\u015fle\u015fme yoksa, sol tablonun s\u00fctunlar\u0131 i\u00e7in NULL<\/code> de\u011ferler g\u00f6sterilir.<\/p>\n
SELECT\n    Musteriler.MusteriAd,\n    Siparisler.SiparisTarihi\nFROM\n    Musteriler\nRIGHT JOIN\n    Siparisler ON Musteriler.MusteriID = Siparisler.MusteriID;\n<\/pre>\n
<\/code><\/p>\n
FULL OUTER JOIN: Her \u0130ki Tablodaki T\u00fcm Kay\u0131tlar<\/h4>\n
FULL OUTER JOIN<\/code>, her iki tablodaki t\u00fcm kay\u0131tlar\u0131 d\u00f6nd\u00fcr\u00fcr. E\u015fle\u015fme olmayan yerlerde NULL<\/code> de\u011ferler g\u00f6sterilir. Bu JOIN t\u00fcr\u00fc, her iki taraftaki t\u00fcm veriyi g\u00f6rmek istedi\u011finizde kullan\u0131\u015fl\u0131d\u0131r.<\/p>\n
SELECT\n    Musteriler.MusteriAd,\n    Siparisler.SiparisTarihi\nFROM\n    Musteriler\nFULL OUTER JOIN\n    Siparisler ON Musteriler.MusteriID = Siparisler.MusteriID;\n<\/pre>\n
<\/code><\/p>\n
Di\u011fer JOIN T\u00fcrleri: CROSS JOIN ve SELF JOIN<\/h3>\n
CROSS JOIN: Kartezyen \u00c7arp\u0131m<\/h4>\n
CROSS JOIN<\/code>, iki tablodaki t\u00fcm olas\u0131 sat\u0131r kombinasyonlar\u0131n\u0131 d\u00f6nd\u00fcr\u00fcr. Bu, bir tablonun her sat\u0131r\u0131n\u0131 di\u011fer tablonun her sat\u0131r\u0131yla birle\u015ftirir. Genellikle test senaryolar\u0131nda veya belirli istatistiksel analizlerde kullan\u0131l\u0131r.<\/p>\n
SELECT\n    Urunler.UrunAd,\n    Renkler.RenkAdi\nFROM\n    Urunler\nCROSS JOIN\n    Renkler;\n<\/pre>\n
<\/code><\/p>\n
SELF JOIN: Ayn\u0131 Tabloyu Kendisiyle Birle\u015ftirme<\/h4>\n
SELF JOIN<\/code>, bir tabloyu kendi kendisiyle birle\u015ftirmektir. Bu, ayn\u0131 tablodaki sat\u0131rlar\u0131 birbiriyle kar\u015f\u0131la\u015ft\u0131rmak veya hiyerar\u015fik verileri sorgulamak i\u00e7in kullan\u0131l\u0131r. \u00d6rne\u011fin, bir \u00e7al\u0131\u015fan\u0131n y\u00f6neticisini bulmak gibi.<\/p>\n
SELECT\n    E.CalisanAd AS Calisan,\n    Y.CalisanAd AS Yonetici\nFROM\n    Calisanlar E\nINNER JOIN\n    Calisanlar Y ON E.YoneticiID = Y.CalisanID;\n<\/pre>\n
<\/code><\/p>\n
Alt Sorgular\u0131n (Subqueries) G\u00fcc\u00fc: Karma\u015f\u0131k Sorgular\u0131 Basitle\u015ftirme<\/h2>\n
Alt sorgular (subqueries), ba\u015fka bir SQL sorgusu i\u00e7inde yer alan sorgulard\u0131r. Bu teknik, karma\u015f\u0131k problemleri daha k\u00fc\u00e7\u00fck, y\u00f6netilebilir par\u00e7alara ay\u0131rarak \u00e7\u00f6zmenize olanak tan\u0131r. Alt sorgular, SELECT<\/code>, FROM<\/code>, WHERE<\/code> veya HAVING<\/code> yan t\u00fcmcelerinde kullan\u0131labilir.<\/p>\n
SELECT \u0130\u00e7inde Alt Sorgular (Scalar Subqueries)<\/h3>\n
SELECT<\/code> yan t\u00fcmcesinde kullan\u0131lan alt sorgular, tek bir de\u011fer d\u00f6nd\u00fcrmelidir (skaler de\u011fer). Genellikle ana sorgunun her sat\u0131r\u0131 i\u00e7in \u00e7al\u0131\u015ft\u0131r\u0131l\u0131r ve o sat\u0131rla ilgili ek bir bilgi sa\u011flar.<\/p>\n
SELECT\n    UrunAd,\n    Fiyat,\n    (SELECT AVG(Fiyat) FROM Urunler) AS OrtalamaFiyat\nFROM\n    Urunler;\n<\/pre>\n
<\/code><\/p>\n
FROM \u0130\u00e7inde Alt Sorgular (Derived Tables)<\/h3>\n
FROM<\/code> yan t\u00fcmcesinde kullan\u0131lan alt sorgular, ge\u00e7ici bir tablo (t\u00fcretilmi\u015f tablo) olu\u015fturur. Bu, ana sorgunun daha sonra bu ge\u00e7ici tablo \u00fczerinde i\u015flem yapmas\u0131na olanak tan\u0131r. \u00d6zellikle ara sonu\u00e7lar\u0131 grupland\u0131rmak veya filtrelemek istedi\u011finizde kullan\u0131\u015fl\u0131d\u0131r.<\/p>\n
SELECT\n    OrtalamaSiparis.MusteriID,\n    OrtalamaSiparis.OrtalamaTutar\nFROM\n    (SELECT MusteriID, AVG(ToplamTutar) AS OrtalamaTutar FROM Siparisler GROUP BY MusteriID) AS OrtalamaSiparis\nWHERE\n    OrtalamaSiparis.OrtalamaTutar > 100;\n<\/pre>\n
<\/code><\/p>\n
WHERE \u0130\u00e7inde Alt Sorgular: Filtreleme G\u00fcc\u00fc<\/h3>\n
WHERE<\/code> yan t\u00fcmcesinde kullan\u0131lan alt sorgular, ana sorgunun sonu\u00e7lar\u0131n\u0131 filtrelemek i\u00e7in kullan\u0131l\u0131r. Bu alt sorgular genellikle IN<\/code>, NOT IN<\/code>, EXISTS<\/code>, NOT EXISTS<\/code>, ALL<\/code>, ANY<\/code> gibi operat\u00f6rlerle birlikte kullan\u0131l\u0131r.<\/p>\n
IN ve EXISTS ile Alt Sorgular<\/h4>\n
IN<\/code> operat\u00f6r\u00fc, bir de\u011ferin alt sorgu taraf\u0131ndan d\u00f6nd\u00fcr\u00fclen bir listede olup olmad\u0131\u011f\u0131n\u0131 kontrol eder. EXISTS<\/code> ise alt sorgunun herhangi bir sat\u0131r d\u00f6nd\u00fcr\u00fcp d\u00f6nd\u00fcrmedi\u011fini kontrol eder ve genellikle IN<\/code>'den daha performansl\u0131 olabilir, \u00f6zellikle b\u00fcy\u00fck veri k\u00fcmelerinde.<\/p>\n
-- IN ile:\nSELECT MusteriAd FROM Musteriler WHERE MusteriID IN (SELECT MusteriID FROM Siparisler WHERE SiparisTarihi > '2023-01-01');\n\n-- EXISTS ile:\nSELECT MusteriAd FROM Musteriler M WHERE EXISTS (SELECT 1 FROM Siparisler S WHERE S.MusteriID = M.MusteriID AND S.SiparisTarihi > '2023-01-01');\n<\/pre>\n
<\/code><\/p>\n
Korelasyonlu Alt Sorgular (Correlated Subqueries)<\/h3>\n
Korelasyonlu alt sorgular, ana sorgudan gelen de\u011ferlere ba\u011fl\u0131d\u0131r ve ana sorgunun her sat\u0131r\u0131 i\u00e7in bir kez \u00e7al\u0131\u015ft\u0131r\u0131l\u0131r. Bu, onlar\u0131 skaler alt sorgulara benzer k\u0131lar, ancak genellikle WHERE<\/code> yan t\u00fcmcesinde daha karma\u015f\u0131k ko\u015fullar i\u00e7in kullan\u0131l\u0131rlar.<\/p>\n
SELECT\n    UrunAd,\n    Fiyat\nFROM\n    Urunler U1\nWHERE\n    Fiyat > (SELECT AVG(Fiyat) FROM Urunler U2 WHERE U2.KategoriID = U1.KategoriID);\n<\/pre>\n
<\/code><\/p>\n
Geli\u015fmi\u015f Sorgulama Teknikleri: Verimlilik ve Esneklik<\/h2>\n
SQL, sadece JOIN'ler ve alt sorgularla s\u0131n\u0131rl\u0131 de\u011fildir. Daha karma\u015f\u0131k veri manip\u00fclasyonlar\u0131 ve analizleri i\u00e7in bir dizi geli\u015fmi\u015f teknik sunar.<\/p>\n
CTE'ler (Common Table Expressions): Okunabilirli\u011fi Art\u0131rma<\/h3>\n
CTE'ler, tek bir sorgu i\u00e7inde referans al\u0131nabilen ge\u00e7ici, adland\u0131r\u0131lm\u0131\u015f sonu\u00e7 k\u00fcmeleridir. Karma\u015f\u0131k sorgular\u0131 daha k\u00fc\u00e7\u00fck, okunabilir ve y\u00f6netilebilir par\u00e7alara ay\u0131rmak i\u00e7in kullan\u0131l\u0131rlar. Ayr\u0131ca, \u00f6zyinelemeli sorgular yazmak i\u00e7in de temel olu\u015ftururlar.<\/p>\n
WITH YuksekFiyatliUrunler AS (\n    SELECT UrunAd, Fiyat FROM Urunler WHERE Fiyat > 50\n)\nSELECT UrunAd FROM YuksekFiyatliUrunler WHERE UrunAd LIKE 'A%';\n<\/pre>\n
<\/code><\/p>\n
Window Fonksiyonlar\u0131: Analitik G\u00fc\u00e7<\/h3>\n
Window fonksiyonlar\u0131, bir sorgunun sonu\u00e7 k\u00fcmesi i\u00e7indeki bir \"pencere\" (ili\u015fkili sat\u0131r k\u00fcmesi) \u00fczerinde hesaplamalar yapman\u0131za olanak tan\u0131r. Bunlar, s\u0131ralama, numaraland\u0131rma, toplama ve ortalama alma gibi analitik g\u00f6revler i\u00e7in son derece g\u00fc\u00e7l\u00fcd\u00fcr.<\/p>\n
ROW_NUMBER(), RANK(), DENSE_RANK()<\/h4>\n
Bu fonksiyonlar, bir b\u00f6l\u00fcm i\u00e7indeki sat\u0131rlara s\u0131ral\u0131 numaralar atar. ROW_NUMBER()<\/code> benzersiz s\u0131ralama sa\u011flarken, RANK()<\/code> ve DENSE_RANK()<\/code> ayn\u0131 de\u011fere sahip sat\u0131rlar i\u00e7in ayn\u0131 s\u0131ray\u0131 verir (RANK()<\/code> bo\u015fluk b\u0131rak\u0131rken, DENSE_RANK()<\/code> b\u0131rakmaz).<\/p>\n
SELECT\n    UrunAd,\n    KategoriID,\n    Fiyat,\n    ROW_NUMBER() OVER (PARTITION BY KategoriID ORDER BY Fiyat DESC) AS SiraNumarasi\nFROM\n    Urunler;\n<\/pre>\n
<\/code><\/p>\n
LAG() ve LEAD(): \u00d6nceki ve Sonraki De\u011ferler<\/h4>\n
LAG()<\/code> ve LEAD()<\/code> fonksiyonlar\u0131, mevcut sat\u0131rdan belirli bir ofset kadar \u00f6nceki veya sonraki sat\u0131rdaki bir s\u00fctunun de\u011ferini alman\u0131z\u0131 sa\u011flar. Bu, zaman serisi analizi veya ard\u0131\u015f\u0131k olaylar\u0131 kar\u015f\u0131la\u015ft\u0131rmak i\u00e7in kullan\u0131\u015fl\u0131d\u0131r.<\/p>\n
SELECT\n    SiparisID,\n    SiparisTarihi,\n    ToplamTutar,\n    LAG(ToplamTutar, 1, 0) OVER (ORDER BY SiparisTarihi) AS OncekiSiparisTutari\nFROM\n    Siparisler;\n<\/pre>\n
<\/code><\/p>\n
UNION ve UNION ALL: Sonu\u00e7 K\u00fcmelerini Birle\u015ftirme<\/h3>\n
UNION<\/code> ve UNION ALL<\/code> operat\u00f6rleri, iki veya daha fazla SELECT<\/code> ifadesinin sonu\u00e7 k\u00fcmelerini dikey olarak birle\u015ftirir. UNION<\/code>, yinelenen sat\u0131rlar\u0131 kald\u0131r\u0131rken, UNION ALL<\/code> t\u00fcm sat\u0131rlar\u0131 (yinelenenler dahil) d\u00f6nd\u00fcr\u00fcr ve genellikle daha performansl\u0131d\u0131r.<\/p>\n
SELECT MusteriAd FROM Musteriler WHERE Sehir = 'Ankara'\nUNION\nSELECT MusteriAd FROM Musteriler WHERE Sehir = '\u0130stanbul';\n<\/pre>\n
<\/code><\/p>\n
Performans Optimizasyonu ve En \u0130yi Uygulamalar<\/h2>\n
Karma\u015f\u0131k sorgular yazmak kadar, bu sorgular\u0131n performansl\u0131 \u00e7al\u0131\u015fmas\u0131n\u0131 sa\u011flamak da \u00f6nemlidir. Yanl\u0131\u015f kullan\u0131lan JOIN'ler veya alt sorgular, veritaban\u0131 performans\u0131n\u0131 ciddi \u015fekilde etkileyebilir.<\/p>\n
JOIN ve Alt Sorgu Se\u00e7imi<\/h3>\n
Her zaman do\u011fru JOIN t\u00fcr\u00fcn\u00fc se\u00e7mek ve alt sorgular\u0131 dikkatli kullanmak kritik \u00f6neme sahiptir. B\u00fcy\u00fck veri k\u00fcmelerinde EXISTS<\/code> genellikle IN<\/code>'den daha iyi performans g\u00f6sterir. CTE'ler, sorgu planlay\u0131c\u0131n\u0131n sorguyu daha iyi optimize etmesine yard\u0131mc\u0131 olabilir.<\/p>\n
\u0130ndeks Kullan\u0131m\u0131<\/h3>\n
JOIN ko\u015fullar\u0131nda ve WHERE<\/code> yan t\u00fcmcelerinde kullan\u0131lan s\u00fctunlara uygun indeksler eklemek, sorgu performans\u0131n\u0131 dramatik bir \u015fekilde art\u0131rabilir. \u0130ndeksler, veritaban\u0131n\u0131n arad\u0131\u011f\u0131 veriye daha h\u0131zl\u0131 ula\u015fmas\u0131n\u0131 sa\u011flar.<\/p>\n
Sorgu Planlar\u0131n\u0131 Anlamak<\/h3>\n
Veritaban\u0131 sistemleri, bir sorguyu nas\u0131l y\u00fcr\u00fcteceklerini belirlemek i\u00e7in bir \"sorgu plan\u0131\" olu\u015fturur. Bu planlar\u0131 incelemek (EXPLAIN<\/code> veya SHOW PLAN<\/code> gibi komutlarla), performans darbo\u011fazlar\u0131n\u0131 tespit etmenin en etkili yollar\u0131ndan biridir.<\/p>\n
Veri Boyutunu K\u00fc\u00e7\u00fcltme<\/h3>\n
Sorgular\u0131n\u0131zda sadece ihtiyac\u0131n\u0131z olan s\u00fctunlar\u0131 se\u00e7in (SELECT *<\/code> kullanmaktan ka\u00e7\u0131n\u0131n). Ayr\u0131ca, WHERE<\/code> yan t\u00fcmcesiyle m\u00fcmk\u00fcn oldu\u011funca erken filtreleme yaparak i\u015flenecek veri miktar\u0131n\u0131 azalt\u0131n. Bu, \u00f6zellikle b\u00fcy\u00fck tablolarda performans\u0131 \u00f6nemli \u00f6l\u00e7\u00fcde art\u0131r\u0131r.<\/p>\n
Sonu\u00e7<\/h2>\n
SQL'de JOIN'ler, alt sorgular ve geli\u015fmi\u015f sorgulama teknikleri, veritabanlar\u0131ndan en iyi \u015fekilde yararlanmak i\u00e7in vazge\u00e7ilmez ara\u00e7lard\u0131r. INNER<\/code>, LEFT<\/code>, RIGHT<\/code> ve FULL OUTER JOIN<\/code> gibi farkl\u0131 JOIN t\u00fcrlerini anlamak, tablolar aras\u0131ndaki ili\u015fkileri etkili bir \u015fekilde y\u00f6netmenizi sa\u011flar. Alt sorgular, karma\u015f\u0131k problemleri daha k\u00fc\u00e7\u00fck par\u00e7alara b\u00f6lerek \u00e7\u00f6zme esnekli\u011fi sunarken, CTE'ler ve Window fonksiyonlar\u0131 gibi geli\u015fmi\u015f teknikler, veri analizi ve raporlama yeteneklerinizi bir \u00fcst seviyeye ta\u015f\u0131r. Ancak bu teknikleri kullan\u0131rken, performans optimizasyonunu g\u00f6z ard\u0131 etmemek gerekir. Do\u011fru indeksleme, sorgu plan\u0131 analizi ve verimli sorgu yazma pratikleri, veritaban\u0131 uygulamalar\u0131n\u0131z\u0131n h\u0131zl\u0131 ve \u00f6l\u00e7eklenebilir kalmas\u0131n\u0131 sa\u011flayacakt\u0131r. Bu bilgileri ustaca kullanarak, verilerinizden en de\u011ferli i\u00e7g\u00f6r\u00fcleri elde edebilir ve daha bilin\u00e7li kararlar alabilirsiniz.<\/p>\n
SSS (S\u0131k Sorulan Sorular)<\/h2>\n
1. INNER JOIN ile LEFT JOIN aras\u0131ndaki temel fark nedir?<\/h3>\n
INNER JOIN<\/code> sadece her iki tabloda da e\u015fle\u015fen kay\u0131tlar\u0131 d\u00f6nd\u00fcr\u00fcr. E\u011fer bir tabloda e\u015fle\u015fen kay\u0131t yoksa, o kay\u0131t sonu\u00e7 k\u00fcmesinde yer almaz. LEFT JOIN<\/code> ise sol tablodaki t\u00fcm kay\u0131tlar\u0131 ve sa\u011f tabloda e\u015fle\u015fen kay\u0131tlar\u0131 d\u00f6nd\u00fcr\u00fcr. Sa\u011f tabloda e\u015fle\u015fme yoksa, ilgili s\u00fctunlar NULL<\/code> olarak g\u00f6sterilir.<\/p>\n
2. Alt sorgular her zaman JOIN'lerden daha m\u0131 yava\u015ft\u0131r?<\/h3>\n
Her zaman de\u011fil. Baz\u0131 durumlarda alt sorgular daha okunabilir ve hatta baz\u0131 veritaban\u0131 sistemleri taraf\u0131ndan JOIN'lere benzer \u015fekilde optimize edilebilir. Ancak genellikle, \u00f6zellikle b\u00fcy\u00fck veri k\u00fcmelerinde ve korelasyonlu alt sorgularda, iyi optimize edilmi\u015f bir JOIN ifadesi daha performansl\u0131 olabilir. EXISTS<\/code> kullan\u0131lan alt sorgular, IN<\/code> kullan\u0131lan alt sorgulardan daha performansl\u0131 olma e\u011filimindedir.<\/p>\n
3. CTE'ler (Common Table Expressions) ne zaman kullan\u0131lmal\u0131d\u0131r?<\/h3>\n
CTE'ler, \u00f6zellikle karma\u015f\u0131k sorgular\u0131 daha okunabilir ve y\u00f6netilebilir par\u00e7alara b\u00f6lmek istedi\u011finizde kullan\u0131lmal\u0131d\u0131r. Ayr\u0131ca, ayn\u0131 ara sonu\u00e7 k\u00fcmesini birden fazla kez kullanman\u0131z gerekti\u011finde veya \u00f6zyinelemeli sorgular yazarken (\u00f6rne\u011fin hiyerar\u015fik verileri sorgulamak i\u00e7in) \u00e7ok faydal\u0131d\u0131rlar.<\/p>\n
4. Window fonksiyonlar\u0131 ile GROUP BY aras\u0131ndaki fark nedir?<\/h3>\n
GROUP BY<\/code>, sat\u0131rlar\u0131 gruplar ve her grup i\u00e7in tek bir \u00f6zet sat\u0131r\u0131 d\u00f6nd\u00fcr\u00fcr (\u00f6rne\u011fin, her kategori i\u00e7in toplam sat\u0131\u015f). Bu, orijinal sat\u0131r detaylar\u0131n\u0131 kaybeder. Window fonksiyonlar\u0131 ise sat\u0131rlar\u0131 gruplamaz; bunun yerine, her orijinal sat\u0131r i\u00e7in bir \"pencere\" (ili\u015fkili sat\u0131r k\u00fcmesi) tan\u0131mlar ve bu pencere \u00fczerinde bir hesaplama yapar. Orijinal sat\u0131r detaylar\u0131 korunur ve hesaplama sonucu her sat\u0131r\u0131n yan\u0131nda g\u00f6sterilir.<\/p>\n
5. Sorgu performans\u0131n\u0131 art\u0131rmak i\u00e7in en \u00f6nemli ipucu nedir?<\/h3>\n
En \u00f6nemli ipucu, sorgular\u0131n\u0131zda sadece ihtiyac\u0131n\u0131z olan verileri \u00e7ekmek ve m\u00fcmk\u00fcn oldu\u011funca erken filtreleme yapmakt\u0131r. SELECT *<\/code> yerine belirli s\u00fctunlar\u0131 se\u00e7in ve WHERE<\/code> yan t\u00fcmcesini kullanarak gereksiz sat\u0131rlar\u0131 eleyin. Ayr\u0131ca, JOIN ko\u015fullar\u0131nda ve filtreleme s\u00fctunlar\u0131nda uygun indeksler kullanmak da kritik \u00f6neme sahiptir.<\/p>\n","protected":false},"excerpt":{"rendered":"Veritabanlar\u0131, modern uygulamalar\u0131n ve i\u015f s\u00fcre\u00e7lerinin temelini olu\u015fturur. 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