10 RESULTS · 1–10
Matches for “SQL joins”
Lesson
SQL JOIN
Line tables up through keys, keep only matching pairs with INNER JOIN, and check whether a one-to-many join multiplies rows.
Lesson
SQL LEFT JOIN
Preserve the left-side population, treat NULL as no match, and avoid a WHERE that silently turns the outer join inner.
Lesson
SQL Self Join
Give one table two roles with aliases, then walk a bridge table when many rows relate to many others.
Lesson
SQL Indexes
Add an access path for real filters and joins, keep the column naked, and pay the extra cost on INSERT, UPDATE, and DELETE.
Lesson
SQL Project: Production Data
Connect tables, keys, joins, transactions, indexes, and injection-safe lookups in one production-minded catalog.
Lesson
SQL UNION
Stack queries that share a shape, choose whether duplicates remain, and remember UNION is not a relationship join.
Lesson
SQL Views
Give a reusable query a name, hide a join behind a stable interface, and treat a stored snapshot as a different fact.
Course
Learn SQL
Learn SQL: query, filter, and sort data; insert, update, and delete rows; design tables with keys; join related data; group results; and use indexes and transactions.
Exercise
Build a complete department enrollment summary
Create an operations report that keeps every department—even departments with no courses—while counting its published courses and active enrollments. The joins must not inflate the course count, unpublished courses and cancelled enrollments must not contribute, and the final rows must be ordered by active demand.
Exercise
Print a receipt from related tables
Build Ada's receipt for order 1. Join customers, orders, order_lines, and products so each line shows display_name, order_id, sku, product name, qty, and line_cents (qty times unit_cents). Keep only order 1.