PostgreSQL Tutorial - 15. Data Query Language (DQL)

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15.1 Introduction to Data Query Language (DQL)

Overview of DQL and its role in database management

Importance of DQL for retrieving and manipulating data

Comparison between DQL and other SQL languages (DDL, DML, DCL)

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15.2 SELECT Statement

Retrieving data from one or more tables using SELECT

Specifying columns in the SELECT clause

Filtering data using the WHERE clause

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15.3 JOIN Operations

Performing inner joins between tables

Using aliases for table names

Performing outer joins (LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN)

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15.4 Subqueries

Writing subqueries within SELECT, FROM, WHERE, and HAVING clauses

Correlated vs. non-correlated subqueries

Using subqueries for filtering and aggregation

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15.5 Set Operations

Combining query results with UNION, INTERSECT, and EXCEPT

Understanding set operations and their usage

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15.6 Aggregate Functions

Calculating aggregate values (e.g., SUM, AVG, COUNT, MAX, MIN)

Using aggregate functions with GROUP BY clause

Filtering grouped data with HAVING clause

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15.7 Window Functions

Introduction to window functions for advanced analytics

Performing calculations across rows with window functions

Ranking, partitioning, and aggregating data using window functions

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15.8 String and Date Functions

Common string functions (e.g., CONCAT, SUBSTRING, UPPER, LOWER, REPLACE)

Date and time functions for manipulating date/time data

Formatting date/time values

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15.9 Pivoting and Unpivoting Data

Transforming rows into columns with PIVOT operation

Unpivoting columns into rows with UNPIVOT operation

Using pivot and unpivot for data analysis and reporting

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15.10 Dynamic SQL

Introduction to dynamic SQL and its usage

Building SQL statements dynamically at runtime

Executing dynamic SQL using EXECUTE statement

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15.11 Common Table Expressions (CTEs)

Understanding common table expressions (CTEs)

Using CTEs for temporary result sets and recursive queries

Advantages and usage scenarios of CTEs

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15.12 Query Optimization

Techniques for optimizing DQL queries for performance

Understanding query execution plans and optimization strategies

Improving query performance with indexing and statistics

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