SQL Practice Problems 57 beginning, intermediate, and advanced challenges for you to solve using a learn-by-doing approach (Sylvia Moestl Vasilik)（Z-Library）

【One-Line Pitch】 A hands-on SQL workbook that builds real querying skill through 57 progressively harder problems on a realistic sample database, rather than through syntax lectures. Best for people who already know basic SQL keywords and want the problem-solving reps that job interviews and data work actually demand. 【Book Arc】 - **Opening (~0%–8%)**: Sets up the learn-by-doing philosophy, explains what the book deliberately omits (exhaustive syntax, cross-vendor comparisons, INSERT/UPDATE/DELETE), and walks you through installing MS SQL Server Express and the sample database. - **Early (~8%–31%)**: Warm-up problems on single-table filtering, sorting, and formatting—WHERE clauses, IN vs. multiple ORs, CONVERT for dates, and basic aggregation like counting products per category. - **Early–Middle (~31%–46%)**: Introduces joins and grouping: LEFT JOIN to find customers with no orders, self-joins, derived tables, and CTEs, plus the classic "accidental double-entry" debugging exercise where you fix buggy SQL. - **Middle (~46%–62%)**: Moves into business-flavored analysis—late orders per employee, fixing NULLs, integer-division pitfalls, high-value customer identification, and flexible customer grouping via a threshold table. - **Late (~62%–85%)**: Advanced multi-step problems: countries with suppliers or customers, self-joins with meaningful aliases, date-difference calculations between consecutive orders, and comparing alternative solutions (LEFT JOIN/IS NULL vs. NOT IN vs. NOT EXISTS). - **Ending (~85%+)**: The remaining problems and answer discussions reinforce good programming practice, readability, and choosing among equivalent approaches—the excerpts do not cover the final problems in detail. 【Key Takeaways】 - **The book teaches SQL by problem-solving, not by syntax reference** (Opening): it assumes you can look up keywords and instead trains you to analyze a data question and work toward a query. (Opening) - **Filtering fundamentals get real-world treatment** (Early): WHERE with IN, <>, and multi-value lists, plus formatting dates with CONVERT—small skills that recur constantly. (Early) - **Joins are the hinge of the whole book** (Early–Middle): LEFT JOIN to find non-matching rows, self-joins for comparisons, and derived tables/CTEs for multi-step logic. (Early–Middle) - **Debugging broken SQL is treated as a core skill** (Middle): the double-entry problem gives you buggy SQL returning 20 rows instead of 16 and asks you to find why. (Middle) - **Aggregation plus business logic is where intermediate skill lives** (Middle): late-order counts per salesperson, NULL-to-zero fixes, and integer-division traps that silently corrupt percentages. (Middle) - **Flexible, data-driven grouping beats hard-coded thresholds** (Middle): using a CustomerGroupThreshold table so boundaries can change without editing SQL. (Middle) - **Multiple correct solutions exist, and the book discusses trade-offs** (Late): LEFT JOIN/IS NULL, NOT IN, and NOT EXISTS are compared, with readability and performance noted. (Late) - **Readable SQL is an explicit goal** (Late): meaningful table aliases, one filter value per line, and clear naming are presented as professional practice. (Late) 【Reading Tips】 - **Do the problems before reading the answers.** The hints are tiered for harder questions—use the first hint, try again, and only then read the discussion. Passive reading defeats the book's purpose. - **Deep-read the discussion sections even when your query works.** They contain alternative approaches and pitfalls (integer division, NULL handling, discount math) that are the real transferable lessons. - **Skim the setup chapter if you already have a SQL environment**, but do load the sample database—every problem depends on its schema and expected results. - **Treat the middle section as the hard wall.** Joins, CTEs, and derived tables are where most learners stall; slow down there rather than rushing to the advanced problems. - **Keep a personal snippet file** of patterns you got wrong (NOT EXISTS, self-join aliases, date functions) and revisit them before interviews. 【Coverage Limits】 This guide is based on stratified excerpts covering the book's framing, setup, and a sampling of problems from early through late sections; the excerpts do not cover every one of the 57 problems or the full answer discussions, so specific later problems may differ from the patterns described here.