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LessonsLearn

Find practical lessons, one concept at a time.

159 lessons

Relational foundations5

What relational databases storeSQL · 3 min read
Tables, rows, columns, and data valuesSQL · 2 min read
Primary keys and relationshipsSQL · 3 min read
How SQL Server fits into a data applicationSQL · 3 min read
Set up a safe SQL Server practice environment and sample databaseSQL · 4 min read

Reading data with SELECT6

SELECT and FROMSQL · 3 min read
Column and table aliasesSQL · 2 min read
DISTINCT and duplicate resultsSQL · 2 min read
Calculated columnsSQL · 2 min read
TOP and OFFSET/FETCHSQL · 2 min read
Logical query processing orderSQL · 2 min read

Filtering and sorting7

WHERE and comparison operatorsSQL · 2 min read
AND, OR, and NOTSQL · 2 min read
IN and BETWEENSQL · 2 min read
LIKE and pattern matchingSQL · 2 min read
IS NULL and missing valuesSQL · 2 min read
ORDER BYSQL · 2 min read
Deterministic pagingSQL · 2 min read

Data types and expressions7

SQL Server data typesSQL · 2 min read
CAST, CONVERT, and safe conversionsSQL · 2 min read
CASE expressionsSQL · 2 min read
COALESCE and NULLIFSQL · 2 min read
Text functionsSQL · 2 min read
Numeric functionsSQL · 2 min read
Date and time functionsSQL · 2 min read

Aggregation6

COUNT, SUM, AVG, MIN, and MAXSQL · 2 min read
GROUP BYSQL · 2 min read
HAVINGSQL · 2 min read
Conditional aggregationSQL · 2 min read
ROLLUP and grouping setsSQL · 2 min read
Avoiding misleading aggregate resultsSQL · 2 min read

Joins and set operations7

Join keys and relationship cardinalitySQL · 2 min read
INNER JOINSQL · 2 min read
LEFT and RIGHT OUTER JOINSQL · 2 min read
FULL OUTER JOIN and CROSS JOINSQL · 2 min read
Self joinsSQL · 2 min read
UNION, UNION ALL, INTERSECT, and EXCEPTSQL · 2 min read
Diagnosing duplicate or missing rows after joinsSQL · 2 min read

Subqueries and CTEs6

Scalar and multi-row subqueriesSQL · 2 min read
EXISTS and NOT EXISTSSQL · 2 min read
Correlated subqueriesSQL · 2 min read
Common table expressionsSQL · 2 min read
Recursive CTEsSQL · 2 min read
Derived tables and APPLYSQL · 2 min read

Modifying data safely6

INSERTSQL · 2 min read
UPDATESQL · 2 min read
DELETESQL · 2 min read
The OUTPUT clauseSQL · 2 min read
Safe update-or-insert patternsSQL · 2 min read
Previewing changes and rolling them backSQL · 2 min read

Tables and integrity7

CREATE TABLE and choosing column typesSQL · 2 min read
Primary keys and foreign keysSQL · 2 min read
UNIQUE, CHECK, NOT NULL, and DEFAULT constraintsSQL · 2 min read
ALTER TABLESQL · 2 min read
DROP TABLE versus TRUNCATE TABLESQL · 2 min read
IDENTITY and sequencesSQL · 2 min read
Normalization and practical schema designSQL · 3 min read

Window functions7

OVER and PARTITION BYSQL · 2 min read
ROW_NUMBERSQL · 2 min read
RANK and DENSE_RANKSQL · 2 min read
LAG and LEADSQL · 2 min read
Running totalsSQL · 2 min read
Moving aggregates and window framesSQL · 2 min read
Top-N results per groupSQL · 2 min read

Transactions and concurrency6

BEGIN TRANSACTION, COMMIT, and ROLLBACKSQL · 2 min read
Savepoints and nested-transaction behaviorSQL · 3 min read
ACID and transaction boundariesSQL · 2 min read
SQL Server isolation levelsSQL · 3 min read
Locks, blocking, and deadlocksSQL · 2 min read
TRY/CATCH and XACT_STATE for safe error handlingSQL · 2 min read

Views, indexes, and query performance7

Create and use viewsSQL · 2 min read
What an index doesSQL · 2 min read
Clustered and nonclustered indexesSQL · 2 min read
Read an execution planSQL · 2 min read
Searchable predicates and SARGabilitySQL · 2 min read
Statistics and cardinality estimatesSQL · 2 min read
A repeatable query-tuning workflowSQL · 3 min read

Advanced T-SQL and application patterns7

Stored procedures and parametersSQL · 2 min read
User-defined functionsSQL · 2 min read
Temporary tables and table variablesSQL · 2 min read
Safe dynamic SQL and injection preventionSQL · 2 min read
Querying JSON in SQL ServerSQL · 2 min read
Database permissions and least privilegeSQL · 2 min read
End-to-end SQL Server capstoneSQL · 3 min read

Getting started with Python6

What Python doesPython · 2 min read
Set up your Python workspacePython · 2 min read
Run your first Python scriptPython · 2 min read
Output and commentsPython · 2 min read
Edit, save, and rerunPython · 2 min read
Read and fix basic errorsPython · 3 min read

Python fundamentals6

Variables and assignmentPython · 2 min read
Numbers, text, and Boolean valuesPython · 2 min read
Arithmetic operatorsPython · 2 min read
Strings and formatted outputPython · 2 min read
Input and type conversionPython · 2 min read
Project: study-time calculatorPython · 2 min read

Decisions and loops5

Comparisons and Boolean logicPython · 2 min read
Choose with if, elif, and elsePython · 2 min read
Repeat with for and rangePython · 2 min read
While loops, break, and continuePython · 2 min read
Project: seven-day study planPython · 2 min read

Collections6

Lists and indexingPython · 2 min read
Tuples and unpackingPython · 2 min read
Dictionaries and key lookupPython · 2 min read
Sets and unique valuesPython · 2 min read
Slicing and comprehensionsPython · 2 min read
Project: study trackerPython · 2 min read

Functions5

Define and call functionsPython · 2 min read
Parameters and return valuesPython · 2 min read
Local scopePython · 2 min read
Type hints and docstringsPython · 2 min read
Project: reusable study summaryPython · 2 min read

Working with text and files5

Useful string methodsPython · 2 min read
Paths and text filesPython · 2 min read
Read and write CSVPython · 2 min read
Read and write JSONPython · 2 min read
Project: save a study logPython · 2 min read

Errors and debugging5

Read tracebacks and common errorsPython · 2 min read
Handle expected errorsPython · 2 min read
Raise clear errors for invalid valuesPython · 2 min read
Debug with small checks and loggingPython · 2 min read
Project: resilient study log readerPython · 3 min read

Modules and environments5

Imports and the standard libraryPython · 1 min read
Create and import your own modulePython · 2 min read
Main guards and packagesPython · 1 min read
Virtual environments and dependenciesPython · 2 min read
Project: reusable study reportPython · 1 min read

Testing Python code5

Assertions and test casesPython · 1 min read
Write tests with unittestPython · 2 min read
Test boundaries and errorsPython · 2 min read
Test isolation and temporary filesPython · 1 min read
Project: test a study summaryPython · 2 min read

Classes and objects5

Classes and instancesPython · 1 min read
Instance methods and statePython · 1 min read
Dataclasses for recordsPython · 1 min read
Composition and inheritancePython · 1 min read
Project: validated study sessionsPython · 2 min read

Iterators and generators5

Iterables and iteratorsPython · 1 min read
Generator functions and yieldPython · 1 min read
Generator expressionsPython · 1 min read
Enumerate, zip, and lazy processingPython · 2 min read
Project: stream study durationsPython · 1 min read

Practical data workflows5

Data records and schema checksPython · 1 min read
Clean and validate CSV rowsPython · 2 min read
Group and aggregate recordsPython · 1 min read
Export results reproduciblyPython · 1 min read
Project: validated study reportPython · 2 min read

What Git tracks1

What Git tracksGit · 2 min read

Your first repository1

Your first repositoryGit · 6 min read

Inspecting changes1

Inspecting changesGit · 7 min read

Branching1

BranchingGit · 7 min read

Merging1

MergingGit · 7 min read

Remotes and collaboration1

Remotes and collaborationGit · 7 min read

Undo and recovery1

Undo and recoveryGit · 6 min read

Clean up commit history1

Clean up commit historyGit · 6 min read

Team workflows1

Team workflowsGit · 6 min read

Advanced tools1

Advanced toolsGit · 7 min read

Git internals1

Git internalsGit · 6 min read

Troubleshooting1

TroubleshootingGit · 7 min read