DBMS 📂 SQL · 4 of 6 23 min read Updated Jun 14, 2026

Interactive SQL Join Playground — Build Queries with WHERE & AND, See Live Results

A hands-on, no-backend SQL join simulator you embed directly in a web page. Learners select two or three related tables (students, attendance, activities — all keyed on roll_no), pick a join type (INNER, LEFT, RIGHT, FULL OUTER), and optionally layer WHERE and AND filters on course, date, and period_no. The matching SQL statement and the resulting rows render live and animated, with NULLs shown explicitly so the difference between inner and outer joins

Interactive Lab

SQL Join Playground — Build a Query, Watch the Result

Pick two or three tables, choose a join type, then tick any combination of conditions — course (subject), date, and period_no — which are combined with AND automatically. Choose whether they go in WHERE (present students only) or in the JOIN ... ON clause (which keeps absentees as NULL with a Present/Absent column). The matching SQL and the resulting rows update live, with the join links animating between the tables you select.

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How the Join Key Works Here

All three tables share roll_no. Every join below matches rows on roll_no. Watch what happens to Esha (no attendance), roll 106 (attendance but no student), and roll 107 (activity but no student) as you switch between INNER and OUTER joins.

👤 students

roll_no	name	branch
101	Asha	CSE
102	Bilal	CSE
103	Chen	ECE
104	Diya	ME
105	Esha	ECE

📋 attendance

roll_no	course	date	period_no
101	DBMS	2024-03-01	1
101	OS	2024-03-01	2
102	DBMS	2024-03-01	1
103	DBMS	2024-03-02	3
104	OS	2024-03-02	2
106	DBMS	2024-03-01	1

Note: roll 106 has attendance but no matching student row.

🎯 activities (extra-curricular)

roll_no	activity	role
101	Robotics	Lead
102	Coding Club	Member
103	Music	Member
105	Sports	Captain
107	Drama	Member

Note: roll 107 has an activity but no matching student row.

🔗 Live Schema — selected tables & active join links

1 Choose tables (pick 2 or 3)

👤 students 📋 attendance 🎯 activities

2 Choose join type

INNER JOIN LEFT JOIN RIGHT JOIN FULL OUTER JOIN

3 Add conditions (optional)

Apply conditions in: WHERE · present only JOIN ON · show absentees

course (subject)

date

period_no

Generated SQL

Result

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Things to Try

Switch students + attendance from INNER to LEFT — Esha appears with NULL course. Switch to RIGHT — roll 106 appears with no name. Add WHERE course = 'DBMS' on a LEFT join and notice the NULL rows vanish: a WHERE filter on an outer-joined column silently turns it back into an inner result.

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Seeing Absent Students — WHERE vs JOIN ... ON

To answer "who was absent for DBMS on 2024-03-01, period 1?" the condition must go in the JOIN ... ON clause, not WHERE. In Step 3, switch "Apply conditions in" to JOIN ON and pick LEFT JOIN: every student is kept, the attendance columns fill in for those who attended that exact session, and everyone else shows Absent with NULL attendance. The same condition in WHERE deletes those NULL rows, so the absentees disappear — which is the situation you were running into.