PostgreSQL UNION
UNION
UNION operatori ikki yoki undan ortiq so‘rovlarning natijalar to‘plamini birlashtirish uchun ishlatiladi.
Uyushmadagi so‘rovlar quyidagi qoidalarga muvofiq bo‘lishi kerak:
- Ular bir xil sonli ustunlarga ega bo‘lishi kerak
- Ustunlar bir xil ma’lumotlar turlariga ega bo‘lishi kerak
- Ustunlar bir xil tartibda bo‘lishi kerak
Misol
UNION operatori yordamida mahsulotlar va sinov mahsulotlarini birlashtiring:
SELECT
product_id, product_name
FROM products
UNION
SELECT
testproduct_id, product_name
FROM testproducts
ORDER BY product_id;
Misolni ishga tushirish »
UNION vs UNION ALL
UNION operatori bilan, agar ikkita so‘rovdagi ba’zi qatorlar aynan bir xil natijani qaytarsa, faqat bitta qator ro‘yxatga olinadi, chunki UNION faqat alohida qiymatlarni tanlaydi.
Takroriy qiymatlarni ham qaytarish uchun UNION ALL dan foydalaning.
Natijada takroriy qiymatlarga ega bo‘lishimiz uchun so‘rovlarga ba’zi o‘zgarishlar kiritamiz:
Misol - UNION
SELECT
product_id
FROM products
UNION
SELECT
testproduct_id
FROM testproducts
ORDER BY product_id;
Misolni ishga tushirish »
Misol - UNION ALL
SELECT
product_id
FROM products
UNION ALL
SELECT
testproduct_id
FROM testproducts
ORDER BY product_id;
Misolni ishga tushirish »
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