How can I apply Logical Operator to 2 Select statement?

Question

I have 4 tables named A, B, C, D. I have 2 conditons to get the data

Condition 1

Select *
From A, B, C
Where //All 3 tables are joined with conditions
limit 1; // Display 1 data at a time

Condition 2

Select *
From A, B, D
Where //All 3 tables are joined with conditions
limit 1; // Display 1 data at a time

What I am looking for is to combine above 2 Select Statement such that

If Data Exists in Condition 1 then Display Data OR Display Data from condition 2

How can I acheieve above functionality?

`mysql` and `postgresql` are different databases, why have you tagged both? *(Pick **one**.)* — MatBailie, Apr 14 '21 at 15:12
on the second query do a WHERE NOT EXISTS()....and union query 1 to the new query 2 — Cato, Apr 14 '21 at 15:15

score 2 · Answer 1 · answered Apr 14 '21 at 15:20

2

You can do it like this

if exists(/*First query*/)
begin

/*FirstQuery*/

end

else

begin

/*Second Query*/

end

answered Apr 14 '21 at 15:20

bhunter338

31
3

How can I use above approach in `js file`? – A Indu Apr 14 '21 at 18:04

score 0 · Answer 2 · answered Apr 14 '21 at 15:21

0

I was thinking of

Select *
From A, B, C
Where //All 3 tables are joined with conditions
limit 1 // Display 1 data at a time
UNION
Select *
From A, B, D
Where not exists(Select *
From A, B, C
Where //All 3 tables are joined with conditions)
limit 1

answered Apr 14 '21 at 15:21

Cato

3,652
9
12

This will not give desired output as in `2nd where clause` we are not defining `By what conditions we need data in 2nd WHERE CLAUSE` – A Indu Apr 14 '21 at 18:15
Does it makes sense what I am trying to say? – A Indu Apr 14 '21 at 18:26

How can I apply Logical Operator to 2 Select statement?

2 Answers2