add: indexes

sql/full_course/indexes/indexes.sql

@@ -0,0 +1,23 @@
+-- INDEX (BTree data structure)
+-- Indexes are used to find values within a specific column more quickly
+-- MySQL normally searches sequentially through a column
+-- The longer the column, the more expensive the operation is
+-- UPDATE takes more time, SELECT takes less time
+SELECT * FROM customers;
+
+SHOW INDEXES FROM customers;
+
+CREATE INDEX last_name_idx
+ON customers(last_name);
+
+SELECT * FROM customers
+WHERE last_name = "Puff";
+
+CREATE INDEX last_name_first_name_idx
+ON customers(last_name, first_name);
+
+ALTER TABLE customers
+DROP INDEX last_name_idx;
+
+SELECT * FROM customers
+WHERE last_name = "Puff" AND first_name = "Poppy";