Are the queries used in mssql, mysql, oracle databases are the same? Which one is widely used?

They are not same at all,

MS SQL is used with .NET Framework,

MYSQL is usually used with Php.

Most of the open source projects uses MySQL. But MsSQL has more security than MySQL.Both are DBMS's Products.MySql requires less spaces on disk, and uses less cpu.

Not all queries are same it is difference from DBMS and other .MySQL is widely used.

each one of those RDBMSs has its own keywords, but ingeneral DML statements are same, DDL and DCL have more platform-oriented manners.Most differences apear when dealing with stored procedures and programmability objects.

Queries (SELECT, DELETE, INSERT, UPDATE ..) are the same.

They differ in some details regarding AutoIncrement, data types and some other details ..

Not all queries are same.MySQL is widely used.

No, they are not same. Widely used database is Mysql

Conceptualize if you see all the database engines follow the RDBMS system (i.e Codd rules).

Syntax may vary from one db to another db.

MSSQL is from Microsoft.

MYSQL is an open source DB.

Oracle is a popular DB from Oracle corporation widely used for its security in large enterprise applications.

Mostly people prefer to use MySql db because its a freeware.

Yes (SQL mean structural query language)

MS SQL Server uses Transact SQL which is an extension of SQL originally developed by Sybase and used by Microsoft. Oracle, meanwhile, uses PL/SQL, or Procedural Language/SQL, the widely used is mysql ;