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. 

What's in the database?

Explore table sizes

Count missing values

Join tables

The keys to the database

Foreign keys

Read an entity relationship diagram

Coalesce

Column types and constraints

Effects of casting

Summarize the distribution of numeric values

What's in the Database?

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.

Numeric data types and summary functions

Division

Explore with division

Summarize numeric columns

Summarize group statistics

Exploring distributions

Truncate

Generate series

More summary functions

Correlation

Mean and Median

Creating temporary tables

Create a temp table

Create a temp table to simplify a query

Insert into a temp table

Summarizing and Aggregating Numeric Data

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.

Character data types and common issues

Count the categories

Spotting character data problems

Cases and spaces

Trimming

Exploring unstructured text

Splitting and concatenating text

Concatenate strings

Split strings on a delimiter

Shorten long strings

Strategies for multiple transformations

Create an "other" category

Group and recode values

Create a table with indicator variables

Exploring Categorical Data and Unstructured Text

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.  

Date/time types and formats

ISO 8601

Date comparisons

Date arithmetic

Completion time by category

Date/time components and aggregation

Date parts

Variation by day of week

Date truncation

Aggregating with date/time series

Find missing dates

Custom aggregation periods

Monthly average with missing dates

Time between events

Longest gap

Rats!

Wrap-up

Working with Dates and Timestamps

Stack Overflow Question Counts

Fortune 500 Companies

Evanston 311 Help Requests

Course Database Creation Code

Course Database Entity Relationship Diagram

You have access to a database. Now what do you do? Building on your existing skills joining tables,  using basic functions, grouping data, and using subqueries, the next step in your SQL journey is  learning how to explore a database and the data in it.  Using data from Stack Overflow, Fortune 500 companies, and 311 help requests  from Evanston, IL, you'll get familiar with numeric, character, and date/time data types. You'll use  functions to aggregate, summarize, and analyze data without leaving  the database. Errors and inconsistencies in the data won't stop you!  You'll learn common problems to look for  and strategies to clean up messy data. By the end of this course, you'll be ready to start exploring your  own PostgreSQL databases and analyzing the data in them.

Data Manipulation in SQL

Learn what's available in a database in SQL, including the tables, relationships, and data stored in them so you can explore your own PostgreSQL databases.

Exploratory Data Analysis in SQL

Learn how to explore what's available in a database: the tables, relationships between them, and data stored in them.

Associate Data Analyst in SQL

SQL for Business Analysts

ISO 8601

Exploratory Data Analysis in SQL

Hands-on interactive exercise