Select all rows in table A if another table B has rows in mysql

Question

In mysql database, I have two tables A and B and would like to select

• all rows in table A if table B has any rows
• no rows in table A if table B has no records

How should I write my SQL query?

Table A and B have columns id and name .

Answer 1

Just check in the where-condition, if b has any rows:

SELECT a.*
FROM a
WHERE EXISTS(SELECT 1 FROM b);