SQL
INNER JOIN Explained
INNER JOIN keeps only rows that match on both sides. Learn the syntax, how the join condition works, and why unmatched rows silently disappear.
JOIN
INNER, LEFT, RIGHT, FULL, CROSS and self joins, multi table joins and unmatched rows.
5 notes
Notes
SQL
LEFT JOIN and RIGHT JOIN
Outer joins keep unmatched rows and fill the missing side with NULL. Learn LEFT and RIGHT JOIN, and the one mistake that silently turns an outer join...
SQL
FULL OUTER JOIN, CROSS JOIN and SELF JOIN
The three joins people meet last: keeping unmatched rows from both sides, deliberate Cartesian products, and joining a table to itself.
SQL
Multiple Joins, Join Conditions and Aliases
Building queries across four or more tables: reading a join chain, non equality conditions, join order, and keeping a long query readable.
SQL
Duplicate Rows from Joins and Finding Unmatched Records
Why a join multiplies rows, how to detect it, and the anti join patterns that answer "which rows have no match at all".