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Essential SQL commands for database queries and management

8 min read
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Official Docs

Basic Queries

Fundamental SQL commands

SELECT Statements

Query data from tables

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💡 Use WHERE to filter results
✅ Always specify ORDER BY for consistent results
⚡ LIMIT improves performance on large tables

Data Modification

Insert, update, and delete data

INSERT, UPDATE, DELETE

Modify table data

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⚠️ Always use WHERE with UPDATE/DELETE
💡 Use transactions for related operations
✅ Test with SELECT before DELETE

Joins

Combine data from multiple tables

JOIN Operations

Combine tables

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💡 INNER JOIN only returns matching rows
✅ LEFT JOIN includes all left table rows
⚡ Index foreign keys for better JOIN performance

Aggregation

Group and aggregate data

GROUP BY & Aggregates

Summarize data

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💡 GROUP BY required for non-aggregate columns
✅ HAVING filters after grouping
⚡ Window functions don't reduce rows

Table Management

Create and modify database structure

DDL Commands

Data Definition Language

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💡 Use appropriate data types and sizes
✅ Always define primary keys
⚡ Add indexes on frequently queried columns

Advanced Queries

Complex query patterns

Subqueries & CTEs

Advanced query techniques

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💡 CTEs improve readability
✅ EXISTS often faster than IN
⚡ Use indexes for subquery joins

Indexes & Performance

Index Management

Create and manage indexes to optimize query performance

📄 Codesql
💡 Indexes speed up SELECT but slow down INSERT/UPDATE
⚠️ Too many indexes can hurt performance
📌 Use EXPLAIN to verify index usage
✅ Create indexes on columns used in WHERE, JOIN, ORDER BY

Transactions

Transaction Control

Manage database transactions for data consistency and isolation

📄 Codesql
💡 Transactions ensure ACID properties
⚠️ Long transactions can cause lock contention
📌 Use appropriate isolation level for your needs
✅ Always handle transaction errors properly

Window Functions

Window Function Syntax

Perform calculations across rows while keeping individual row details

📄 Codesql
💡 Window functions don't reduce rows like GROUP BY
⚡ More efficient than self-joins for many calculations
📌 Use PARTITION BY to group calculations
✅ Frame clauses control which rows are included

Constraints & Keys

Table Constraints

Define rules and relationships to maintain data integrity

📄 Codesql
💡 Constraints enforce data integrity at database level
⚠️ Foreign keys can impact performance on large tables
📌 Name your constraints for easier management
✅ Use NOT NULL for required fields

Views

View Management

Create virtual tables based on SELECT queries for data abstraction

📄 Codesql
💡 Views simplify complex queries and provide abstraction
⚡ Materialized views cache results for better performance
📌 Use views for security by hiding sensitive columns
✅ Views are updated automatically when base tables change