The relationship between SQL and No SQL is not competitive but complementary.
SQL is stable and consistent and No SQL is flexible and scalable.
SQL is better for data which needs more consistency and accuracy, like payment and finance. No SQL is better for data which can tolerate some inconsistency like logs and user preference.
SQL examples: MySQL, PostgreSQL, Oracle and SQL Server.
No SQL examples: Riak (key-value), Neo4j (graph) and MongoDB (document).
New platforms (New SQL) combines both SQL and NoSQL: VoltDB, FoundationDB and NuoDB.
reference: SQL and NoSQL(Link)