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Category: SQL
Data cleaning in SQL is a crucial step in data preprocessing, especially when working with real-world messy datasets. Below is a structured breakdown of SQL data cleaning steps, methods, functions, and complex use cases you can apply in real projects or interviews. ✅ Common SQL Data Cleaning Steps & Methods Step Method / Function Example…
Understanding how an SQL query executes in a database is essential for performance tuning and system design. Here’s a step-by-step breakdown of what happens under the hood when you run an SQL query like: 🧭 0. Query Input (Your SQL) You submit the SQL query via: ⚙️ Step-by-Step SQL Query Execution 🧩 Step 1: Parsing…
Here’s a comprehensive guide to important and tricky conceptual issues in SQL, including NULL behavior, joins, filters, grouping, ordering, and subqueries. ✅ 1. NULLs: The #1 source of confusion a. NULL ≠ NULL b. NOT IN with NULL c. Arithmetic with NULL ✅ 2. JOIN Issues a. INNER JOIN drops unmatched rows. b. LEFT JOIN…
Here’s a comprehensive, logically structured, and interactive guide to SQL Indexing, consolidating and enhancing all the content you’ve shared, complete with real examples, platform-specific insights, and advanced use cases: 🧠 Mastering Indexing in SQL: A Complete Guide 🔍 What is Indexing in SQL? Indexing is a performance optimization technique that allows fast retrieval of rows…
3. SQL Command Categories Overview SQL commands are classified into five main categories based on their functionality: Category Acronym Description DDL Data Definition Language Define/alter schema structure (tables, views, indexes) DML Data Manipulation Language Modify data (insert, update, delete) DCL Data Control Language Manage user access (privileges) TCL Transaction Control Language Control transaction flow (commit,…
PIVOT Clause in Spark sql or Mysql or Oracle Pl sql or Hive QL The PIVOT clause is a powerful tool in SQL that allows you to rotate rows into columns, making it easier to analyze and report data. Here’s how to use the PIVOT clause in Spark SQL, MySQL, Oracle PL/SQL, and Hive QL:…