Well, I created a table called installments, which when the customer pays it is entered 'PAYMENT' in the column situation, and when not paid it remains blank. I wanted to get the information from this column to know when the account was not paid, so bring only the customers that have the column empty.
Example:
select * from parcela where situacao =''
But do not bring the data from the table situation and when I put:
select * from parcela where situacao ='PAGO'
It brings the data perfectly