CREATE TABLE CUSTOMER (CustomerId VARCHAR2, FirstName VARCHAR2)
CREATE TABLE INVOICE (InvoiceDate VARCHAR2, CustomerId VARCHAR2)

Find all invoice dates corresponding to customers with first name Astrid and last name Gruber.
SELECT T2.InvoiceDate FROM CUSTOMER AS T1 JOIN INVOICE AS T2 ON T1.CustomerId = T2.CustomerId WHERE T1.FirstName = "Astrid" AND LastName = "Gruber"
SELECT "T2"."InvoiceDate" FROM "CUSTOMER" "T1" JOIN "INVOICE" "T2" ON "T1"."CustomerId" = "T2"."CustomerId" WHERE "Astrid" = "T1"."FirstName" AND "Gruber" = "LastName"