The essential SQL Mastery cheat sheet: 8 concise chapters you can read in minutes, distilled from the full deck. When you're ready, drill the flashcards or test yourself under exam conditions.
SQL, or Structured Query Language, is the standardized language used to manage relational databases—databases that organize data into tables connected through defined relationships...
Read full chapter →Designing tables thoughtfully is essential to avoid anomalies when data is inserted, updated, or deleted. Normalization is the systematic process of organizing tables to reduce red...
Read full chapter →The SELECT statement is the heart of SQL data retrieval. A query begins by specifying source tables with FROM, then filters rows using WHERE, groups rows with similar values using...
Read full chapter →Real-world queries almost always span more than one table, which is where joins come in. A JOIN combines rows from two or more tables based on a related column, typically a primary...
Read full chapter →Aggregate functions summarize sets of rows. COUNT(*) tallies every row including NULLs, COUNT(column) tallies non-NULL values, and COUNT(DISTINCT column) counts unique non-NULL val...
Read full chapter →Beyond reading data, SQL defines ways to create, modify, and remove both rows and the structures that hold them. The CRUD operations—Create, Read, Update, Delete—correspond to INSE...
Read full chapter →Beyond plain queries, SQL offers ways to encapsulate logic and reshape results. A Common Table Expression (CTE), introduced with WITH, names a subquery so that the main query can r...
Read full chapter →Indexes are the most important tool for query performance. A B-tree index—the most common kind—supports equality and range lookups, a hash index supports only equality, a unique in...
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