Dampak urutan operasi pada struktur kueri

World Bank memiliki data untuk banyak negara, tetapi mereka kekurangan nilai untuk beberapa tahun. Anda memutuskan mencari negara yang memiliki setidaknya satu tahun data populasi yang hilang. Anda menulis kueri berikut, tetapi kueri tersebut TIDAK berjalan.

SELECT olympic_cc, COUNT(*)
FROM demographics
WHERE population IS NULL
AND COUNT(*) > 1

Anda merujuk catatan Anda tentang urutan operasi SQL untuk memahami alasannya.

Manakah dari berikut ini yang menjelaskan kesalahan logisnya?

Latihan ini adalah bagian dari kursus

Meningkatkan Performa Kueri di PostgreSQL

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Mulai berolahraga

Latihan ini adalah bagian dari kursus

Meningkatkan Performa Kueri di PostgreSQL

SkillTag.level.intermediateSkillTag.label

4.8+

Mulai Kursus Gratis

Bundle up as you dive into the Winter Olympics! You will learn how to join, subquery, and create temporary tables while finding which Olympic athletes brave sub-freezing temperatures to train. You will also learn about the query planner and how its functionality can guide your SQL structure to faster queries.

Exercise 1: All about joins Exercise 2: Where are all the athletes from Exercise 3: Using different joins to explore athletes' regions Exercise 4: What about the weather Exercise 5: Subqueries and common table expressions (cte)Exercise 6: Filtering to freezing with a subquery Exercise 7: Where winter is white Exercise 8: Countries with subqueries or CTEs Exercise 9: Working with temporary tables Exercise 10: Canadians temp table Exercise 11: Analyze that temp table

Dig up those past algebra memories while learning the SQL order of operations. Find which countries "should" have the most athletes by looking at population and gross domestic product (GDP) while learning the best way to filter. You will also learn when your query aggregates (sums, counts, etc.) and how you can structure your query to optimize this process.

Exercise 1: Apa yang Anda tulis bukanlah yang dilihat SQL Exercise 2: Dampak urutan operasi pada struktur kueri

Latihan Saat Ini

Exercise 3: Group by dan agregasi Exercise 4: COUNT dan COUNT DISTINCT Exercise 5: Menyaring dengan klausa WHERE Exercise 6: OR versus IN dengan atlet Exercise 7: Filter tipe data Exercise 8: EXPLAIN langkah rencana kueri untuk filter Exercise 9: Menyaring saat melakukan join Exercise 10: Di mana meletakkan filter wilayah Exercise 11: Memfilter di join, where, dan select Exercise 12: Mengagregasi dengan granularitas data yang berbeda Exercise 13: Agregasikan sebelum menggabungkan tabel Exercise 14: Tren Afrika Selatan

Zero in on the properties that improve database performance. Discover when your table is not a table but a view. Learn how your database's storage structure (row or column oriented) impacts your query structure. You will explore volcanic smog while using partitions and indexes to speed your queries.

Exercise 1: Queries and tables and views, oh my Exercise 2: Data loading and storage Exercise 3: Finding the table type Exercise 4: Row-oriented storage and partitions Exercise 5: Row-oriented storage properties Exercise 6: Previewing a row-oriented table Exercise 7: Partitioning on location Exercise 8: Using and creating indexes Exercise 9: Finding the database indexes Exercise 10: Creating and using an index Exercise 11: Compare runtimes Exercise 12: Using column-oriented storage Exercise 13: Column-oriented storage properties Exercise 14: Using the information schema

Learn the lingo of the Query Lifecycle and dive into the query planner. Explore how the query planner creates and optimizes the query plan. Find your next vacation locale by looking for countries with recent population growth while also seeing how a join impacts the query steps. Fine tune your optimization techniques by seeing how different filters speed your query times.

Exercise 1: Query lifecycle and the planner Exercise 2: Exploring pg_tables Exercise 3: Basic EXPLAIN Exercise 4: Index scans Exercise 5: EXPLAIN the WHERE Exercise 6: A deeper dive into EXPLAIN Exercise 7: EXPLAIN parameters Exercise 8: Aggregating and sorting populations Exercise 9: Joining in the query plan Exercise 10: Query structure and query execution Exercise 11: Subqueries vs. CTEs Exercise 12: Why the difference?Exercise 13: Filtering impacts Exercise 14: Congratulations