It appeared in 1974. SQL is one of the often used languages for maintaining the relational database. SQL. In 1986 SQL become the standard of American National Standards Institute (ANSI) and ISO(International Organization for Standardization) in 1987.

SQL, or Structured Query Language, first appeared in the early 1970s. It was developed by IBM researchers Donald D. Chamberlin and Raymond F. Boyce. The initial version, called SEQUEL (Structured English Query Language), was designed for managing and manipulating relational databases. SQL has since become the standard language for interacting with relational database management systems (RDBMS), and it has undergone various standardization efforts.

So, the correct answer to “When did SQL appear?” would be in the early 1970s.