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<!DOCTYPE html>
<html>
<head>
<title>Advanced Analysis with SQL - NYC Parks</title>
<meta charset="utf-8">
<link rel="stylesheet" href="slide.css"/>
</head>
<body>
<textarea id="source">
layout:true
<div class="header" style="display:block; text-align: left; color:gray; font-size:1em; position: fixed; top: 0px; left: 0px; height: 30px;vertical-align:middle;margin:7px 0 0 0;width:100%;background: #fcfcfc;
background: -moz-linear-gradient(top, #fcfcfc 0%, #d1d1d1 100%);
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background: linear-gradient(to bottom, #fcfcfc 0%,#d1d1d1 100%);
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#fcfcfc', endColorstr='#d1d1d1',GradientType=0 );">
<img src="images/datapolitan_transparent_small.png" style="position: fixed;top: 2px; left: 5px; width: 14%;">
<p style="display:block;text-align:left;color:gray;font-size:1em; position: fixed; top: 0px; left: 155px; height: 30px;vertical-align:middle;margin:7px 0 0 0; ">Advanced Analysis with SQL - NYC Parks and Recreation</p>
</div>
<div class="footer" style="display:block;color:gray;position:fixed;bottom: 0px;left:0px;height:30px;vertical-align:middle;margin:0 0 0 0;width:100%;background: #fcfcfc;background: -moz-linear-gradient(top, #fcfcfc 0%, #d1d1d1 100%);background: -webkit-linear-gradient(top, #fcfcfc 0%,#d1d1d1 100%);background: linear-gradient(to bottom, #fcfcfc 0%,#d1d1d1 100%);sfilter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#fcfcfc', endColorstr='#d1d1d1',GradientType=0 );">
<p class="footer">
<span xmlns:dct="http://purl.org/dc/terms/" property="dct:title">Advanced Analysis with SQL</span> by <a xmlns:cc="http://creativecommons.org/ns#" href="http://www.datapolitan.com" target="_blank" property="cc:attributionName" rel="cc:attributionURL">Richard Dunks</a> and <a xmlns:cc="http://creativecommons.org/ns#" href="http://ebrelsford.github.io" property="cc:attributionName" rel="cc:attributionURL">Eric Brelsford</a> is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike 4.0 International License</a>.<a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/"><img alt="Creative-Commons-License" style="border-width:0" src="https://i.creativecommons.org/l/by-sa/4.0/80x15.png" /></a>
</p>
</div>
<!-- <p class="footer">
<span xmlns:dct="http://purl.org/dc/terms/" property="dct:title">Data Analytics for NYC Parks</span> by <a xmlns:cc="http://creativecommons.org/ns#" href="http://www.datapolitan.com" property="cc:attributionName" rel="cc:attributionURL">Richard Dunks</a> and <a xmlns:cc="http://creativecommons.org/ns#" href="http://www.tinypanther.pizza" property="cc:attributionName" rel="cc:attributionURL">Julia Marden</a> is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike 4.0 International License</a>.<a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/"><img alt="Creative-Commons-License" style="border-width:0" src="https://i.creativecommons.org/l/by-sa/4.0/80x15.png" /></a>
</p> -->
--
class:center, middle
# Advanced Analysis with SQL<br>City of New York Parks and Recreation
- - -
## Instructors: Eric Brelsford and Richard Dunks
## Teaching Assistant: Sarah Kontos
### Follow along at: http://bit.ly/advanced-analysis-sql
#### See the code at: http://bit.ly/advanced-analysis-sql-code
---
class:center,middle
<!-- start of A block -->
# Welcome
???
+ Facilitators and TA introduce themselves, establishing mastery but also creating openings for vulnerability and awareness
---
# A Few Ground Rules
???
+ Facilitators establish the intention we have for the culture of the classroom
--
+ Step up, step back
--
+ One mic
--
+ Be curious and ask questions
--
+ Assume noble regard and positive intent
--
+ Respect multiple perspectives
--
+ Listen to comprehend, not to respond
--
+ Be present (phone, email, social media, etc.)
---
# Introduce Yourself to Your Neighbor
+ Who are you?
+ Where do you work?
+ What has been the proudest moment in your job?
+ What's your favorite national or state park?
???
+ An opportunity for participants to get to know each other and settle into the class
+ We bring them into a positive space related to their work
+ Facilitator reminds them the data isn't the end but the means to achieve the actions that make us feel good about our jobs
---
# Housekeeping
???
+ Facilitator sets expectations with the students
+ Establishes the "contract" for the class
--
+ We’ll have one 15 minute break in the morning
--
+ We’ll have an hour for lunch
--
+ We’ll have a 15 minute break in the afternoon
--
+ Class will start promptly after breaks
--
+ Feel free to use the bathroom if you need during class
--
+ Please take any phone conversations into the hall to not disrupt the class
---
# What to Expect Today
--
+ Introduction to databases
--
+ Introduction to SQL
--
+ Hands-on experience writing and using SQL
--
+ A chance to explore SQL and perform some analysis using it
---
class:center,middle
# Let's Get Started
---
class:center,middle
# A Quick Recap from <br>[Introduction to Data Analytics](http://training.datapolitan.com/parks-intro-analytics/#1)
???
+ Facilitator concludes the walk-through to shift to a discussion of data and analysis
---
# The Value of Data
???
+ Facilitator brings back discussion of the value of data, prompting participants to describe the value of data in their job
+ Optionally, facilitator can ask the value of the data just aggregated and how it might be useful to decisionmakers
--
+ Data tells a story about something that's happened
--
+ Can describe what happened directly or indirectly
--
???
+ Facilitator helps participants see the direct measurements of service requests while indirectly measuring when Park incidents actually happen
---
class: center,middle
# What are some of the data challenges you face?
???
+ Facilitator holds discussion with participants about the data issues they face on a regular basis
+ Facilitator prompts participants to think about their data problems as we go through the data techniques today
---
exclude:true
class:middle
> Facts do not "speak for themselves." They speak for or against competing theories. Facts divorced from theory or visions are mere isolated curiosities.
## -Thomas Sowell *A Conflict of Visions*
---
# What is Analysis?
--
>“Analysis is simply the pursuit of understanding, usually through detailed inspection or comparison”
## - [Carter Hewgley](https://www.linkedin.com/in/carterhewgley), Senior Advisor for Family & Homeless Services, Department of Human Services, District of Columbia
???
+ Facilitator prompts participants to think about analysis in the context of their work and what it is they are trying to accomplish
---
class:center,middle
# A Quick Recap from <br>Data Analysis with Excel I and II
---
# 5 Data Analytics Tasks
???
+ Facilitator introduces the 5 main tasks of analysis
+ Facilitator reminds participants we've talked about these in previous courses
+ We're going to look at the first three in SQL
--
1. Filtering
--
1. Sorting
--
1. Aggregating
--
1. Transforming
--
1. Visualizing
---
class:center,middle
# Importing data into Excel with SQL
???
+ Walk through importing data with SQL into Excel with a simple query
---
# Importing data from a database
+ Click on the **Power Query** ribbon
---
# Importing data from a database
+ Power Query > From Database > From SQL Server Database
---
# Importing data from a database
+ Enter `data.nycdpr.parks.nycnet` in the **Server** field
+ Enter `DWH` in the **Database** field
---
# Encryption Warning
## Just select "OK"
### [For more information](https://docs.microsoft.com/en-us/sql/relational-databases/security/encryption/sql-server-encryption?view=sql-server-2017)
---
# Importing data from a database
+ View the accessible databases
---
# Importing data from a database
+ Find `tbl_ref_calendar` and click **Load** to load it
---
# Importing data from a database
---
class:center,middle
# What did we just do?
---
class:center,middle
# What is a database?
---
# What is a database?
--
+ A software system that manages storing and retrieving data
--
+ The software for a database often runs on a server, not the computer you're using
--
+ There are many different database systems, today we'll be using Microsoft's SQL Server
--
+ A database stores data in *tables*
---
# Tables
--
+ How data is stored in a database
--
+ Similar to a worksheet in Excel
--
+ Organized in *rows* and *columns*
--
--
---
class:center,middle
# Let's do that again using SQL
---
# `SELECT`
--
+ How you specify which columns to get from a table
--
+ Start with `SELECT *`, which gets all the columns
--
+ Separate column names with commas (`,`)
---
# For example:
```sql
SELECT *
FROM tbl_ref_calendar
```
--
+ Get all of the columns from the `tbl_ref_calendar` table
---
# For example:
```sql
SELECT ref_date, fiscal_year
FROM tbl_ref_calendar
```
--
+ Only get the `ref_date` and `fiscal_year` columns from the `tbl_ref_calendar` table
--
---
# `FROM`
--
+ How you specify the table you are querying
--
```sql
FROM tbl_ref_calendar
```
---
class:center,middle
# Why use a database?
???
+ Facilitator walks through benefits of using a database: single source of truth, always the latest data
---
# Why use a database?
--
+ Single source of truth
--
+ Don't have to worry about moving and sharing files
--
+ Can be faster and more consistent than Excel files
---
class:center,middle
# Why use SQL?
???
+ Facilitator walks through benefits of using SQL: you need to in order to communicate with a database, but also it can be self documenting: "here's the query I used" rather than "I clicked here, then there, then picked this option..." in Excel.
---
# SQL
--
+ The language databases understand
--
+ If you want to use a database, you will need at least a little SQL
--
+ It makes queries replicable—you can run the query again and be sure you will get the same results
--
+ ...and someone can use your query and be sure they will get the same results, too!
---
# Editing a query
--
+ You don't have to create a new query each time you want to change the SQL
--
+ If you are experimenting with a query, we recommend *editing* the SQL instead
---
# Editing a query
+ Double click the **Source**
---
# Editing a query
+ Edit the SQL as usual
---
# Your Turn
--
+ We talked about using `SELECT` to pick which columns to pull from a table:
--
```sql
SELECT ref_date, fiscal_year
FROM tbl_ref_calendar
```
--
+ Write a SQL query to get only the `ref_date`, `fiscal_day`, `fiscal_week`, `fiscal_qtr` columns from `tbl_ref_calendar`
--
+ Run the query in Excel
---
# Data Analytics Tasks: Filtering
???
+ Facilitator leads brief discussion of filtering, soliciting examples from participants on applicability to their own work
--
+ Show a preview of rows
--
+ Or only show rows that contain some value
--
+ Can filter by multiple values
--
+ Can filter by values in multiple columns
---
# Daily Tasks
--
+ Labor booking for routine litter and cleaning
--
+ Approximately 78,000 tasks logged a month (~936,000 a year)
--
+ Nearly 3.9 million tasks logged as of Spring 2019
--
+ Can't work with all this data at once
---
# Previewing rows
--
+ You can use `SELECT TOP` to get the first set of rows
--
```sql
SELECT TOP 5 *
FROM tbl_dailytasks
```
--
+ Select the top 5 rows from `tbl_dailytasks`
--
+ Without *sorting* the data this could be any 5 rows—we'll talk about sorting soon
--
+ Can use this to view the column names and the values in the table
--
+ For more information on TOP, [check out this tutorial](http://www.sqlservertutorial.net/sql-server-basics/sql-server-select-top/)
---
# Filtering by column values
???
+ Facilitator reminds students about filtering in Excel
---
# In SQL we use `WHERE`
--
+ Lets you limit which *rows* are selected from the database
--
+ You define a condition that is either true or false, and every row is evaluated using that
???
+ Look back at filters in Excel
+ Do something similar in a WHERE
+ `AND` and `OR`
+ Watch out for precedence with `AND` and `OR`
+ `NULL` vs empty strings
---
# `WHERE`
```sql
SELECT TOP 10 *
FROM tbl_dailytasks
WHERE graffiti = 1
```
--
+ Select the top 10 daily tasks rows where graffiti was present
--
+ Note that we are using `TOP` along with `WHERE` here so we don't load too much data
---
# But `graffiti` is `TRUE` or `FALSE`
--
+ We'll be talking about data types soon, but this column is stored as a `BIT`, which is `1` or `0`
--
+ This is a common way to store values that are true or false
--
+ In this case, Excel is displaying the values at `TRUE` and `FALSE`, but in the database they are `1` or `0`
--
+ Learn more about [BIT here](http://www.sqlservertutorial.net/sql-server-basics/sql-server-bit/)
---
# `WHERE`
```sql
SELECT TOP 10 *
FROM tbl_dailytasks
WHERE nhours > 1
```
--
+ Select the top 10 daily tasks rows where `nhours` is greater than 1
---
# `WHERE` operators
+ `=`
--
- equal to
--
+ `>`
--
- greater than
--
+ `>=`
--
- greater than or equal to
--
+ `<`
--
- less than
--
+ `<=`
--
- less than or equal to
--
+ `!=`
--
and `<>`
--
- not equal to
--
+ Learn more in [the SQL Server documentation](https://docs.microsoft.com/en-us/sql/t-sql/language-elements/comparison-operators-transact-sql?view=sql-server-2017)
---
# Your Turn
+ Create an SQL query with a `WHERE` clause
+ Continue using the `tbl_dailytasks` table
+ Try writing a condition on a column with numbers in it
+ Make sure you limit the results with `TOP`
+ If you have time, try writing a condition on a column with text in it
---
class:center,middle
# What if you want to combine conditions?
---
# `WHERE`
```sql
SELECT TOP 10 *
FROM tbl_dailytasks
WHERE graffiti = 1 AND nhours > 1
```
--
+ Select the daily tasks rows where graffiti was present *and* the number of hours taken was over 1
---
# `WHERE`
```sql
SELECT TOP 10 *
FROM tbl_dailytasks
WHERE omppropid = 'X045-01' OR omppropid = 'X045-02'
```
--
+ Select the daily tasks rows for `omppropid` equal to either `X045-01` or `X045-02`
---
# `WHERE`
```sql
SELECT TOP 10 *
FROM tbl_dailytasks
WHERE NOT (omppropid = 'X045-01' OR omppropid = 'X045-02')
```
--
+ What do you think this does?
--
+ Why would we use parentheses here?
--
+ Learn more about [SQL's order of evaluation](http://www.peachpit.com/articles/article.aspx?p=1276352&seqNum=6) and [propositional logic](https://www.tutorialspoint.com/discrete_mathematics/discrete_mathematics_propositional_logic.htm)
---
# Your Turn
+ Create an SQL query with a `WHERE` clause
+ Continue using the `tbl_dailytasks` table
+ Start with one condition, then try adding conditions using `AND` / `OR`
---
# Documentation
--
+ It never hurts to keep track of your work
--
+ Can help you remember the steps you took
--
+ Can help you find errors in your methods
--
+ In the future, can help you reconstruct your work and adapt it to solve different problems
--
+ Colleagues and your future self will find it helpful
---
class:center,middle
# How should we document SQL work?
---
# Documentation with SQL
--
+ If you're working in Excel, you could use a separate worksheet where you track the steps you have taken
--
---
# Documentation with SQL
+ If you're not working in Excel, you could keep a simple text document in Notepad where you keep track of the queries you're using
--
+ Either way, be sure to track the queries you're using and the date that you accessed the data
--
+ And if you make changes to the data after getting it from the database, track those steps too
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+ The queries we're talking about today are documented in your [today's handout](workbook.pdf)—you can take notes there, too
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# WRAP-UP
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# 15 MIN BREAK
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# Data types
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+ Every column in a database table has a type
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+ A column's type determines what you can do with that column
--
+ For example, you can do math on numbers but not on text
--
+ The database will refuse to store data that doesn't match the column's type
--
+ Unless you're an administrator, you most likely will not be changing the column's type
???
+ Take a look back at data types in Excel
+ Mention that data types are more rigid in a database
+ Integers, numeric, datetime, strings
---
# Common numeric data types
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+ `int`
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- a number with no digits after the decimal point, like `5` or `100349`
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+ `numeric`
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- a number with digits after the decimal point, like `5.01` or `100.349`
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+ `bit`
--
- a number that can only be `0` or `1`; as we mentioned earlier, this is commonly used for boolean (true or false) values
---
# Common text data types
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+ `varchar`
--
- text with a maximum length, like `Queens`
--
+ `text`
--
- text with no maximum length, like an open comment field
---
# Other common data types
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+ `date`
--
- a specific date, like `2002-10-17`
--
+ `datetime`
--
- a specific date and time, like `2002-10-17 06:13:00`
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+ Learn more in the [SQL Server documentation](https://docs.microsoft.com/en-us/sql/t-sql/data-types/data-types-transact-sql?view=sql-server-2017)
---
# Why do data types matter?
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+ Databases and SQL are less flexible than Excel here
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+ Knowing the data type of a column tells you what to expect in that column
--
+ For example: `date` columns will never include time
--
+ Some functions only work on certain data types
---
# What data type should zip codes be stored as?
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+ `numeric`?
--
+ `varchar`?
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+ How do you handle a zip code like **08904**?
--
+ or **11368-3398**?
---
# Working with Data Types
--
+ Can get the information on types from the `INFORMATION_SCHEMA` table:
--
```sql
SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME='tbl_dailytasks'
```
--
+ If you need a column to be a different data type, you might find [`CAST` or `CONVERT` useful](https://docs.microsoft.com/en-us/sql/t-sql/functions/cast-and-convert-transact-sql?view=sql-server-2017)
---
# Your Turn
???
+ Quick demonstration of why data types will matter
+ Instructor could show how `YEAR()` does not work with just any column
--
+ There are functions that work only with specific data types
--
+ For example, `YEAR()` only works on columns that are `date`s
--
+ See other date and time functions in the [SQL Server documentation](https://docs.microsoft.com/en-us/sql/t-sql/functions/date-and-time-data-types-and-functions-transact-sql?view=sql-server-2017#DateandTimeFunctions)
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+ Try selecting the top 10 rows from `tbl_dailytasks` with the columns `date_worked` and `YEAR(date_worked)`
---
# Formulas
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+ You can do arithmetic and combine values in the ways you're used to in Excel
--
+ You can also get a modified version of a value
???
+ Take a look back at arithmetic in Excel
+ You can do arithmetic in SQL, too
+ Order of operations is similar, using parentheses as needed
+ Show equivalent in SQL to something relatively complicated in Excel
+ Introduce `AS` for setting the output column name
---
# Using formulas with numbers
--
+ You can use the usual mathematical operators here:
`+`, `-`, `/`, `*`
--
+ For example, you can multiply a column by a number
--
+ `nhours * 60`
--
would find the number of minutes
--
```sql
SELECT TOP 10 nhours * 60
FROM tbl_dailytasks
```
---
# Using functions with text
--
+ Remember the `LEFT` function in Excel?
--
--
+ It extracts part of a cell's value
---
# Using functions with text
--
+ We can do the same thing with SQL
--
+ `LEFT` extracts part of a string
--
+ The format is `LEFT(column, length)`
--
+ `LEFT(omppropid, 1)` would select the first letter from the `omppropid` column
--
```sql
SELECT TOP 10 LEFT(omppropid, 1)
FROM tbl_dailytasks
```
--
+ Find more functions in the [SQL Server Documentation](https://docs.microsoft.com/en-us/sql/t-sql/functions/string-functions-transact-sql?view=sql-server-2017)
---
# Your Turn