book

Data Wrangling with SQL

Name: Data Wrangling with SQL
ISBN: 9781837630028

by Raghav Kandarpa, Shivangi Saxena

July 2023

Beginner to intermediate

350 pages

9h 39m

English

Packt Publishing

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Data Wrangling with SQL
AcknowledgementsDedicationContributorsAbout the authorsAbout the reviewers
Preface
Who this book is forWhat this book coversTo get the most out of this bookDownload the example code filesConventions usedGet in touchShare Your ThoughtsDownload a free PDF copy of this book
Part 1:Data Wrangling Introduction
Chapter 1: Database Introduction
Getting startedEstablishing the foundationEfficient data organizationData integrity and consistencyTechnical requirementsDecoding database structures – relational and non-relationalWhat is a database?Types of databasesTables and relationshipsThe SQL CREATE DATABASE statementThe SQL CREATE TABLE statementSQL DROP TABLE versus TRUNCATE TABLESQL ALTER TABLESQL constraintsSQL keysDatabase relationshipsComparing database normalization and denormalizationNormalizationTypes of normalizationDenormalizationWhen to apply denormalizationDisadvantages of denormalizationSummaryPractical exercisesPractical exercise 1Practical exercise 2Practical exercise 3Practical exercise 4
Chapter 2: Data Profiling and Preparation before Data Wrangling
What is data wrangling?Data wrangling stepsThe importance of data wranglingBenefits of data wranglingData wrangling use casesBusiness use casesData captureHow does data get captured?Data-capturing techniquesWeb scrapingStructured versus unstructured dataPaid-for versus free data-wrangling toolsData profilingData profiling typesData profiling techniquesPractical exerciseStep 1 – DiscoveryStep 2 – StructuringStep 3 – CleaningStep 4 – EnrichingStep 5 – ValidatingStep 6 – PublishingSummary
Part 2:Data Wrangling Techniques Using SQL
Chapter 3: Data Wrangling on String Data Types
SQL data typesNumeric data typesDate and time data typesString data typeSQL string functionsRIGHT()LEFT()LEN()TRIM()RTRIM()LTRIM()RPAD()LPAD()REPLACE()REVERSE()SUBSTRING()CAST()CONCATENATE()CONCATENATE_WS()UPPER functionLOWER functionINITCAP functionINSTR functionSummaryPractical exercisesPractical exercise 1Practical exercise 2Practical exercise 3Practical exercise 4
Chapter 4: Data Wrangling on the DATE Data Type
SQL DATE data type functionsEXTRACTDATEDIFF()TIMEDIFF()DATE_ADD()DATE_SUB()DATE_FORMAT()STR_TO_DATE()Extracting the current date and timeSummary
Chapter 5: Handling NULL Values
The impact of missing data and NULL values on data analysisUnderstanding the importance of data validation and cleaning before analyzing dataIdentifying NULL/missing valuesNULL values versus zero valuesUsing the IS NULL and IS NOT NULL operators to filter and select data with NULL valuesIS NULL() and IS NOT NULL() – scenarioUsing the COALESCE and IFNULL functions to replace NULL values with a default valueIFNULL()COALESCE()IS NULL versus = NULLSummary
Chapter 6: Pivoting Data Using SQL
SQL Transpose – rows to columnsUse case scenarioSQL Cross Tab – columns to rowsUse case scenarioUnpivoting data in SQLAnalytical workflow – from SQL to business intelligence – transforming data into actionable insightsSummary

Part 3:SQL Subqueries, Aggregate And Window Functions
Chapter 7: Subqueries and CTEs
Introduction to subqueriesSimple subqueriesCorrelated subqueriesUsing subqueries in SELECT statementsUsing subqueries in FROM statementsUsing subqueries in WHERE statementsNested subqueriesCorrelated subqueriesUsing subqueries in INSERT, UPDATE, and DELETE statementsManaging and maintaining subqueriesCommon table expressionsPerformance considerations for subqueries and CTEsSubquery versus CTEsSummary
Chapter 8: Aggregate Functions
Overview of aggregate functions in SQLUsing GROUP BYCOUNT()SUM()AVG()MIN() and MAX()COUNT(DISTINCT)Case scenario – using all aggregate functionsSummary
Chapter 9: SQL Window Functions
The importance of SQL window functionsSQL aggregate functionsSQL window functions versus aggregate functionsWindow functions versus aggregate functions – an example to illustrate the differencesWindow functionsSUM()COUNT()AVG()ROW_NUMBER()RANK() and DENSE_RANK()Lead() and Lag()NTILE()Summary
Part 4:Optimizing Query Performance
Chapter 10: Optimizing Query Performance
Introduction to query optimizationQuery execution planQuery optimization techniquesExampleCachingNormalizationQuery monitoring and troubleshootingQuery profilingQuery loggingDatabase monitoringTips and tricks for writing efficient queriesSummaryIn the next chapter, we will learn about descriptive statistics using SQL, which will provide us with insights into the distribution, central tendency, and variability of data, which can, in turn, help us identify outliers and anomalies. Common SQL functions and statements used for descriptive statistics include COUNT, AVG, MIN, MAX, and GROUP BY. By using SQL to analyze data, researchers and analysts can efficiently extract and summarize information from large datasets.
Part 5:Data Science And Wrangling
Chapter 11: Descriptive Statistics with SQL
Calculating descriptive statistics with SQLMeanMedianModeStandard deviationVarianceVariabilitySummaryIn the next chapter, we will learn how SQL can be used for time series analysis.
Chapter 12: Time Series with SQL
Running totalsCase scenarioLead and lag for time series analysisCase scenarioKey KPIsPercentage changeCase scenarioKey KPIsMoving averagesCase scenarioKey KPIsRank for time series analysisCase scenarioKey KPIsCTE for time series analysisImportance of using CTEs while performing time series analysisForecasting with linear regressionCase scenarioKey KPIsSummaryIn the next chapter, we will learn different methods to find outliers in the data easily. Outlier detection is an important aspect of data analysis as it helps determine if the data is correct, looks at the skewness of the data, and removes any unexpected values.
Chapter 13: Outlier Detection
Measures of central tendency and dispersionCase scenarioKey KPIsMethods for detecting outliersBox plot methodHandling outliersCase scenarioKey points to keep in mind while handling outliersApplying outlier detectionChallenges and limitationsBest practicesSummary
Index
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Content preview from Data Wrangling with SQL

5 Handling NULL Values

In this chapter, we will delve into the crucial aspects of dealing with missing data and NULL values during the data analysis process. We will explore the profound impact that these gaps in data can have on the accuracy and validity of our analyses if not appropriately addressed. By emphasizing the significance of data validation and cleaning prior to analysis, we will highlight the importance of ensuring accurate, complete, and relevant data in drawing meaningful conclusions and facilitating informed decision-making.

We will begin by unraveling the distinction between NULL values and 0, shedding light on their different meanings within the context of data analysis. Recognizing this distinction serves as the foundation ...

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Data Wrangling with SQL

by Raghav Kandarpa, Shivangi Saxena

5

Handling NULL Values

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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