if SQL is query language for all the databases then their must be common syntax too ?
They all are sql engines, but utilitiez different syntax because they process it in different manner. So for example Oracle, MySQL uses PLSQL where as Sybase, MS SQL Server uses TSQL. All these standards are ANSI compliant but have different logic as per ther engine. This gives audience an option as well as more features and ease to individual, which differs person to person.
Databases mean servers like MySQL , oracle db, db2 etc.
What do you mean by all databases ? please elaborate