Practical sql: a beginner’s Guide to Storytelling with Data pdfdrive com
tải về 5.77 Mb. Chế độ xem pdf
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BASIC MATH AND STATS WITH SQL Math Operators Math and Data Types Adding, Subtracting, and Multiplying Division and Modulo Exponents, Roots, and Factorials Minding the Order of Operations Doing Math Across Census Table Columns Adding and Subtracting Columns Finding Percentages of the Whole Tracking Percent Change Aggregate Functions for Averages and Sums Finding the Median Finding the Median with Percentile Functions Median and Percentiles with Census Data Finding Other Quantiles with Percentile Functions Creating a median() Function Finding the Mode Wrapping Up Try It Yourself 6 JOINING TABLES IN A RELATIONAL DATABASE Linking Tables Using JOIN Relating Tables with Key Columns Querying Multiple Tables Using JOIN JOIN Types JOIN LEFT JOIN and RIGHT JOIN FULL OUTER JOIN CROSS JOIN Using NULL to Find Rows with Missing Values Three Types of Table Relationships One-to-One Relationship One-to-Many Relationship Many-to-Many Relationship Selecting Specific Columns in a Join Simplifying JOIN Syntax with Table Aliases Joining Multiple Tables Performing Math on Joined Table Columns Wrapping Up Try It Yourself 7 TABLE DESIGN THAT WORKS FOR YOU Naming Tables, Columns, and Other Identifiers Using Quotes Around Identifiers to Enable Mixed Case Pitfalls with Quoting Identifiers Guidelines for Naming Identifiers Controlling Column Values with Constraints Primary Keys: Natural vs. Surrogate Foreign Keys Automatically Deleting Related Records with CASCADE The CHECK Constraint The UNIQUE Constraint The NOT NULL Constraint Removing Constraints or Adding Them Later Speeding Up Queries with Indexes B-Tree: PostgreSQL’s Default Index Considerations When Using Indexes Wrapping Up Try It Yourself tải về 5.77 Mb. Chia sẻ với bạn bè của bạn:
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