SQL必知必会（第5版） (福达)（Z-Library）

【One-Line Pitch】 A practical, lesson-based introduction to SQL that takes you from your first SELECT statement to advanced topics like joins, subqueries, and stored procedures—ideal for absolute beginners and developers who need a quick, hands-on reference. 【Book Arc】 - **Opening (~0%–5%)**: Introduces core database concepts (database, table, primary key) and the philosophy of SQL as a simple, purpose-built language. Sets up the sample database used throughout the book. - **Early (~5%–26%)**: Covers basic data retrieval with SELECT, sorting with ORDER BY, and filtering with WHERE, including advanced filtering with AND, OR, NOT, and NULL handling. - **Early–Middle (~26%–37%)**: Explores wildcard filtering with LIKE, calculated fields, concatenation, aliases, and the use of functions—highlighting portability issues across DBMSs. - **Middle (~37%–53%)**: Introduces aggregate functions (COUNT, SUM, AVG, etc.), data grouping with GROUP BY, filtering groups with HAVING, and subqueries for filtering and calculated fields. - **Late (~53%–end)**: Dives into joins (inner, self, natural, outer), table aliases, and combined queries with UNION, then moves to more advanced topics like views, stored procedures, and triggers. 【Key Takeaways】 - **SQL is a small, focused language** (Early): Unlike general-purpose programming languages, SQL has few keywords and is designed solely for reading and writing data. This simplicity is its strength—master the core statements and you can work with any major DBMS. - **Always define a primary key** (Early): A primary key uniquely identifies each row and is essential for reliable updates and deletions. Without it, you risk modifying or removing unintended data. - **Filtering should happen in the database, not in your app** (Early): Using WHERE to filter data at the database level is far more efficient than retrieving everything and filtering in client code. It reduces network traffic and improves scalability. - **Wildcards are powerful but costly** (Early–Middle): LIKE with % and _ enables flexible text matching, but wildcard searches are slower than other filters. Use them judiciously and avoid leading wildcards when possible. - **SQL functions are not portable** (Middle): While functions like RTRIM() and SOUNDEX() are useful, each DBMS has its own syntax and support. Check your DBMS documentation—code that works in one system may fail in another. - **GROUP BY and HAVING work together for grouped analysis** (Middle): GROUP BY organizes data into logical groups for aggregate calculations, while HAVING filters those groups. Remember: WHERE filters rows before grouping; HAVING filters groups after. - **Joins require explicit conditions** (Late): Without a proper join condition, you get a Cartesian product—every row from one table paired with every row from another. Always specify join conditions and be mindful of performance when joining multiple tables. 【Reading Tips】 - **Skim the first lesson if you know basic database terms**: The opening covers database, table, and key concepts. If you're comfortable with these, jump straight to Lesson 2 for SELECT. - **Deep-read Lessons 4–6 on filtering**: WHERE, AND/OR/NOT, and wildcards are the foundation of almost every real-world query. Practice the examples until they feel natural. - **Pay attention to DBMS-specific notes**: The book frequently flags syntax differences (e.g., LIMIT vs. TOP, concatenation with + vs. ||). Highlight these if you're working with a specific database like MySQL or PostgreSQL. - **Do the challenge problems at the end of each lesson**: They reinforce what you've learned and often combine multiple concepts—this is where the real learning happens. - **Use the sample database**: Download or create the example tables described in Appendix A. Running the queries yourself is far more effective than just reading the code. 【Coverage Limits】 This guide covers the core content visible in the excerpts—from basic retrieval through joins and subqueries. The excerpts do not cover the later chapters on views, stored procedures, triggers, and transaction management in detail, though these are mentioned in the table of contents.