Question

Below is my Table Structure

Table 1

id
name


Table 2

id
table1_id

I want the rows from table 1 which have no reference value in table 2.

Example data:

Table 1
id                name                       
1                  demo
2                  demo2
3                  demo3

Table 2

id                table1_id
1                   1
2                   1
3                   1
4                   3
5                   3

So there is no value in table 2 with table1_id 2. I want id 2 from Table 1.

Below id the query i have tried:

SELECT l.id FROM Table1 l WHERE l.id NOT IN (SELECT DISTINCT(r.id) FROM table2 r);

This is returning a proper result but its taking more than 2 minutes to process.

In table 1 i have 4000 rows and in table 2 I have 40000 rows.

Any optimisation to above query or any alternative solution?

Answer 1

SELECT * FROM table1 LEFT JOIN table2
ON table1.id=table2.table1_id
WHERE table2.table1_id IS NULL