What is the difference between MySQL and PostgreSQL?

Son muy similares, los comandos son parecidos, viendolo desde el punto de vista del desarrollador.

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there are a lot of differences here is a link to those differences

MySQL is a relational database management system (RDBMS) currently developed by Oracle with open-source code. This code is available for free under the GNU General Public License, and commercial versions of MySQL are also available under various proprietary agreements. PostgreSQL is an object-RDBMS (ORDBMS) that’s developed by the PostgreSQL Global Development Group. It also has an open source, which is released under the permissive PostgresSQL License.