differences for PR #368

md5sum.txt

@@ -11,6 +11,7 @@
 "episodes/03-sql-joins.md" "4c87f9451d13eaa88c1b38fe29c7a7f3" "site/built/03-sql-joins.md" "2023-06-30"
 "instructors/instructor-notes.md" "105728ef72c768e968ca9d11c2a14109" "site/built/instructor-notes.md" "2023-04-21"
 "learners/discuss.md" "c5994f9f17e9da0d08a530600084ba55" "site/built/discuss.md" "2023-04-21"
-"learners/reference.md" "a9e2e8b2be027afbeb360f1bbd966da2" "site/built/reference.md" "2023-06-09"
+"learners/reference.md" "83dc790413398fce3bb07518546928fa" "site/built/reference.md" "2023-10-19"
 "learners/setup.md" "ba0ada65a673ca1d95ed722b0711fa87" "site/built/setup.md" "2023-06-30"
+"learners/sql-cheat-sheet.md" "fe94973871efccd88f8bc193d359bdb1" "site/built/sql-cheat-sheet.md" "2023-10-19"
 "profiles/learner-profiles.md" "60b93493cf1da06dfd63255d73854461" "site/built/learner-profiles.md" "2023-04-21"

reference.md

@@ -96,7 +96,7 @@ Glosario](https://glosario.carpentries.org/) (CC-BY-4.0)*
 
 ## Commands
 
-See [this cheat sheet](files/sql-cheat-sheet.md) for an list of the commands
+See [this cheat sheet](sql-cheat-sheet.md) for an list of the commands
 covered in this lesson.
 
 ### Keywords

sql-cheat-sheet.md

@@ -0,0 +1,134 @@
+---
+title: SQL Cheat Sheet
+---
+
+Basic Queries
+-------------
+
+Select one or more columns of data from a table:
+
+    SELECT column_name_1, column_name_2 FROM table_name;
+
+Select all of the columns in a table:
+
+    SELECT * FROM table_name;
+
+Get only unique lines in a query:
+
+    SELECT DISTINCT column_name FROM table_name;
+
+Perform calculations in a query:
+
+    SELECT column_name_1, ROUND(column_name_2 / 1000.0) FROM table_name;
+
+
+Filtering
+---------
+
+Select only the data meeting certain criteria:
+
+    SELECT * FROM table_name WHERE column_name = 'Hello World';
+
+Combine conditions:
+
+    SELECT * FROM table_name WHERE (column_name_1 >= 1000) AND (column_name_2 = 'A' OR column_name_2 = 'B');
+
+
+Sorting
+-------
+
+Sort results using `ASC` for ascending order or `DESC` for descending order:
+
+    SELECT * FROM table_name ORDER BY column_name_1 ASC, column_name_2 DESC;
+
+
+Missing Data
+------------
+
+Use `NULL` to represent missing data.
+
+`NULL` is neither true nor false.
+Operations involving `NULL` produce `NULL`, e.g., `1+NULL`, `2>NULL`, and `3=NULL` are all `NULL`.
+
+Test whether a value is null:
+
+    SELECT * FROM table_name WHERE column_name IS NULL;
+
+Test whether a value is not null:
+
+    SELECT * FROM table_name WHERE column_name IS NOT NULL;
+
+
+Grouping and Aggregation
+------------------------
+
+Combine data into groups and calculate combined values in groups:
+
+    SELECT column_name_1, SUM(column_name_2), COUNT(*) FROM table_name GROUP BY column_name_1;
+
+
+Joins
+-----
+
+Join data from two tables:
+
+    SELECT * FROM table_name_1 JOIN table_name_2 ON table_name_1.column_name = table_name_2.column_name;
+
+
+Combining Commands
+------------------
+
+SQL commands must be combined in the following order:
+`SELECT`, `FROM`, `JOIN`, `ON`, `WHERE`, `GROUP BY`, `ORDER BY`.
+
+
+Creating Tables
+---------------
+
+Create tables by specifying column names and types.
+Include primary and foreign key relationships and other constraints.
+
+    CREATE TABLE survey(
+            taken   INTEGER NOT NULL,
+            person  TEXT,
+            quant   REAL NOT NULL,
+            PRIMARY KEY(taken, quant),
+            FOREIGN KEY(person) REFERENCES person(ident)
+    );
+
+Transactions
+------------
+
+Put multiple queries in a transaction to ensure they are ACID
+(atomic, consistent, isolated, and durable):
+
+    BEGIN TRANSACTION;
+      DELETE FROM table_name_1 WHERE condition;
+      INSERT INTO table_name_2 values(...);
+    END TRANSACTION;
+
+Programming
+-----------
+
+Execute queries in a general-purpose programming language by:
+
+* loading the appropriate library
+* creating a connection
+* creating a cursor
+* repeatedly:
+    * execute a query
+    * fetch some or all results
+* disposing of the cursor
+* closing the connection
+
+Python example:
+
+    import sqlite3
+    connection = sqlite3.connect("database_name")
+    cursor = connection.cursor()
+    cursor.execute("...query...")
+    for r in cursor.fetchall():
+        ...process result r...
+    cursor.close()
+    connection.close()
+