Announcements

• Scheme Project Tail Recursion (check spec/discussion)
• Teaching opportunities!
  • CSM
  • AI
• Regular Schedule of HW being due on Thursday
• Scheme
  • Checkpoint 1 due today!
  • Checkpoint 2 due Friday

Notes from last section

• What is my morning routine?
• What is my night routine?
• Good humor/energy
  • 

Temperature Check

• RegEx
• SQL

RegEx

• Regular Expressions are used to describe sets of strings that meet certain criteria
• Very useful for pattern matching (will see examples later)
  • Used in real life all the time!
  • Can be used for super simple patterns (egg in text)
  • Can also be very complicated (validating passwords)
• regex101.com
  • Super useful for learning/debugging your regular expressions, but don't rely on this!
  • (You won't have this resource for the exam! Don't use it as a GPS)

Character Classes

• If you want to search for a certain character in a set of characters, use character classes
• Can use pre-defined classes, or specify your own

Specified:

Character Classes

Predefined character classes

Combining Multiple Patterns

• If you put a pattern after another pattern, you can have a regular expression that matches both of those characters in succession
  • AB - Matches A, then B (both are required)
  • A[xt]e Matches A, then either x or t, then E
    • Axe or Ate are the things that get matched
• | is the separator used to match 'or'
  • A|B - Matches either A or B

Quantifiers

Groups

• Parentheses are used to group certain patterns together
  • Useful with quantifiers
  • (Ha)+ and Ha+ do different things!

Anchors

Special Characters

Some characters cannot be written directly because they have special roles in RegEx

• \[](){}+*?|$^.
• Inside a character class, you need to escape -
• To escape these characters, you need to put a backslash before them
  • The quick brown fox jumped over the lazy dog\.

RegEx in Python

• For Python, we use r-strings to write regex patterns
• With r-strings in Python, backslashes are treated specially in some cases (for example with \n, or \t). What r-strings do in this case is that they automatically escape the backslashes for these special characters, so they look like real backslashes rather than what Python designates for those characters.
• r"<insert string here>" - the r at the front makes a string an r-string
  • Python also has f-strings which are pretty useful/interesting

Ambiguous Joins

• Tables might have overlapping column names
• We need a way to distinguish between these columns
  • Especially if you need to join a table with itself (useful if you want to compare 2 people with each other)
• Use the as keyword

Ambiguous Joins

Aggregation

• Aggregation tends to be useful when you have multiple groups, and you want to group by certain pieces of data.
• You can also combine multiple rows into 1 with aggregation
  • SELECT COUNT(*) FROM RECORDS;
  • SELECT name, MAX(salary) FROM RECORDS;
• GROUP BY will allow you to perform these aggregation functions on specific groups
  • SELECT division, MIN(salary) FROM records GROUP BY division;
• WHERE statements for GROUP BYs uses the HAVING clause
  • HAVING filters out entire groups
  • You can have both WHERE and HAVING in the same statement

Mental Health Resources

• CAPS:
  • If you need to talk to a professional, please call CAPS at 510-642-9494.
• After Hours Assistance
  • For any assistance after hours, details on what to do can be found at this link