Databases
🔗 JOINs: combining tables
Spread information across several related tables and bring it back together with INNER JOIN, LEFT JOIN, aliases and self-join.
What you'll learn
- Combine tables with
INNER JOIN ... ONbased on their foreign keys - Keep rows without a match using
LEFT JOINand detect the unmatched ones withIS NULL - Apply
RIGHT JOIN,FULL OUTER JOINandCROSS JOINas appropriate - Chain several JOINs, abbreviate tables with aliases and perform a self-join
Lessons
Combining tables with INNER JOINBring related tables back together by their foreign key with INNER JOIN ... ON. LEFT JOIN: keeping the left tableKeep all the rows from the left even when they find no match, with NULL on the right. RIGHT JOIN, FULL OUTER JOIN and CROSS JOINKeep the right table, both at once, or combine every row with every row. Several JOINs, aliases and self-joinChain JOINs, abbreviate tables with aliases and join a table with itself (employee → manager).Practice this module in the app
DevPath is a hands-on course: you read the theory here; in the app you put it into practice with exercises that really run, offline.
Start free in the app →