SQL Query Types and Components

Queries

• Types of SQL Queries:
  • DML (Data Manipulation Language): INSERT, UPDATE, DELETE
  • DDL (Data Definition Language): CREATE, DROP, ALTER
  • DQL (Data Query Language): SELECT
  • TCL (Transaction Control Language): COMMIT, ROLLBACK
• Query Components:
  • SELECT: specifies columns to retrieve
  • FROM: specifies tables to retrieve from
  • WHERE: specifies conditions for which rows to retrieve
  • GROUP BY: groups rows based on one or more columns
  • HAVING: specifies conditions for which groups to retrieve
  • ORDER BY: specifies order of retrieved rows
  • LIMIT: limits number of retrieved rows
• Query Optimization:
  • Use indexes to speed up queries
  • Avoid using SELECT * and instead specify only necessary columns
  • Use efficient join types (e.g. INNER JOIN instead of CROSS JOIN)

Normalization

• Goals of Normalization:
  • Eliminate data redundancy and inconsistencies
  • Improve data integrity and scalability
  • Reduce data storage requirements
• Normalization Rules:
  • First Normal Form (1NF): each table cell must contain a single value
  • Second Normal Form (2NF): each non-key attribute must depend on the entire primary key
  • Third Normal Form (3NF): if a table is in 2NF, and a non-key attribute depends on another non-key attribute, then it should be moved to a separate table
• Denormalization:
  • intentional denormalization for performance or simplicity reasons
  • should be done carefully to avoid data inconsistencies

Database Design

• Database Design Principles:
  • Separation of Concerns: each table should have a single, well-defined purpose
  • Data Independence: data should be independent of application logic
  • Data Consistency: data should be consistent across the database
• Entity-Relationship Diagrams (ERDs):
  • visual representation of database design
  • entities (tables) and relationships (foreign keys) are modeled
• Database Schema:
  • defines the structure of the database
  • includes table definitions, relationships, and constraints

Joins

• Types of Joins:
  • INNER JOIN: returns only matching rows from both tables
  • LEFT JOIN: returns all rows from the left table and matching rows from the right table
  • RIGHT JOIN: returns all rows from the right table and matching rows from the left table
  • FULL OUTER JOIN: returns all rows from both tables
  • CROSS JOIN: returns the Cartesian product of both tables
• Join Conditions:
  • Equi-Join: join based on equal values
  • Natural Join: join based on common columns
  • Self-Join: join a table with itself

Indexing

• Types of Indexes:
  • Clustered Index: physical ordering of table rows based on index
  • Non-Clustered Index: separate data structure that contains index keys and pointers to table rows
  • Composite Index: index based on multiple columns
  • Unique Index: ensures uniqueness of indexed column(s)
• Indexing Benefits:
  • improved query performance
  • reduced I/O operations
  • faster data retrieval
• Indexing Considerations:
  • index maintenance overhead
  • additional storage requirements
  • potential negative impact on write performance

SQL Queries

• DML (Data Manipulation Language) queries: INSERT, UPDATE, DELETE
• DDL (Data Definition Language) queries: CREATE, DROP, ALTER
• DQL (Data Query Language) queries: SELECT
• TCL (Transaction Control Language) queries: COMMIT, ROLLBACK
• SELECT specifies columns to retrieve
• FROM specifies tables to retrieve from
• WHERE specifies conditions for which rows to retrieve
• GROUP BY groups rows based on one or more columns
• HAVING specifies conditions for which groups to retrieve
• ORDER BY specifies order of retrieved rows
• LIMIT limits number of retrieved rows

Query Optimization

• Use indexes to speed up queries
• Avoid using SELECT * and specify only necessary columns instead
• Use efficient join types (e.g. INNER JOIN instead of CROSS JOIN)

Normalization

• Goals: eliminate data redundancy and inconsistencies, improve data integrity and scalability, reduce data storage requirements
• First Normal Form (1NF): each table cell must contain a single value
• Second Normal Form (2NF): each non-key attribute must depend on the entire primary key
• Third Normal Form (3NF): if a table is in 2NF, and a non-key attribute depends on another non-key attribute, then it should be moved to a separate table
• Denormalization: intentional denormalization for performance or simplicity reasons, should be done carefully to avoid data inconsistencies

Database Design

• Database Design Principles: Separation of Concerns, Data Independence, Data Consistency
• Separation of Concerns: each table should have a single, well-defined purpose
• Data Independence: data should be independent of application logic
• Data Consistency: data should be consistent across the database
• Entity-Relationship Diagrams (ERDs): visual representation of database design, entities (tables) and relationships (foreign keys) are modeled
• Database Schema: defines the structure of the database, includes table definitions, relationships, and constraints

Joins

• Types of Joins: INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN, CROSS JOIN
• INNER JOIN: returns only matching rows from both tables
• LEFT JOIN: returns all rows from the left table and matching rows from the right table
• RIGHT JOIN: returns all rows from the right table and matching rows from the left table
• FULL OUTER JOIN: returns all rows from both tables
• CROSS JOIN: returns the Cartesian product of both tables
• Join Conditions: Equi-Join, Natural Join, Self-Join
• Equi-Join: join based on equal values
• Natural Join: join based on common columns
• Self-Join: join a table with itself

Indexing

• Types of Indexes: Clustered Index, Non-Clustered Index, Composite Index, Unique Index
• Clustered Index: physical ordering of table rows based on index
• Non-Clustered Index: separate data structure that contains index keys and pointers to table rows
• Composite Index: index based on multiple columns
• Unique Index: ensures uniqueness of indexed column(s)
• Indexing Benefits: improved query performance, reduced I/O operations, faster data retrieval
• Indexing Considerations: index maintenance overhead, additional storage requirements, potential negative impact on write performance

Learn about the different types of SQL queries, including DML, DDL, DQL, and TCL, and their components such as SELECT, FROM, and WHERE clauses.