1. Apprendre
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  2. Cours
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  3. Exploratory Data Analysis in SQL
  • 1

    What's in the Database?

    Gratuit

    Start exploring a database by identifying the tables and the foreign keys that link them. Look for missing values, count the number of observations, and join tables to understand how they're related. Learn about coalescing and casting data along the way.

  • 2

    Summarizing and Aggregating Numeric Data

    You'll build on functions like min and max to summarize numeric data in new ways. Add average, variance, correlation, and percentile functions to your toolkit, and learn how to truncate and round numeric values too. Build complex queries and save your results by creating temporary tables.

  • 3

    Exploring Categorical Data and Unstructured Text

    Text, or character, data can get messy, but you'll learn how to deal with inconsistencies in case, spacing, and delimiters. Learn how to use a temporary table to recode messy categorical data to standardized values you can count and aggregate. Extract new variables from unstructured text as you explore help requests submitted to the city of Evanston, IL.

  • 4

    Working with Dates and Timestamps

    What time is it? In this chapter, you'll learn how to find out. You'll aggregate date/time data by hour, day, month, or year and practice both constructing time series and finding gaps in them.

Initializing

Exercice

Read an entity relationship diagram

The information you need is sometimes split across multiple tables in the database.

What is the most common stackoverflow tag_type? What companies have a tag of that type?

To generate a list of such companies, you'll need to join three tables together.

Reference the entity relationship diagram as needed when determining which columns to use when joining tables.

Instructions 1/2

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  • First, using the tag_type table, count the number of tags with each type.
  • Order the results to find the most common tag type.