Kick Start Guide to SQL interview questions ( for beginners )

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Definition wise, SQL is a language for storing, manipulating, and retrieving data from/to databases.SQL stands for Structured query language. Basically, SQL is an ANSI/ISO standard, there are different versions of SQL languages based on the RDBMS database program used.MySQL, SQL Server, MS Access, Oracle, Sybase, Informix, Postgres, etc.. are some of them. for being compatible with the ANSI standard, they all support at least the major commands (such as SELECT, UPDATE, DELETE, INSERT, WHERE) in a similar manner.

what all SQL Language can do with Databases:
  • Execute queries against a database
  • Retrieve data from a database
  • Insert records in a database
  • Update records in a database
  • Delete records from a database
  • Create new databases
  • Create new tables in a database
  • Create stored procedures in a database
  • Create views in a database
  • Set permissions on tables, procedures, and views

These SQL commands are mainly categorized into four categories as:

  1. DDL – Data Definition Language
  2. DQl – Data Query Language
  3. DML – Data Manipulation Language
  4. DCL – Data Control Language
  • DDL – Data Definition Language
Data Definition Language is used for defining data structures especially database schema.DDL statements create/modify database structures such as tables, indexes, users. These commonly used DDL statements are 
    • CREATE
    • ALTER 
    • DROP
  • DQl – Data Query Language
DQI Language is used to queries in database systems. The DQL statement in all databases is
    • SELECT
  • DML – Data Manipulation Language
DML language used to add, delete, modify data in the database. Commonly Used DML commands are 
    • INSERT
    • DELETE
    • UPDATE
  • DCL – Data Control Language
DCL commands are mainly used to control permissions, rights, other settings of the database. Some of the DCL command examples are 
    • GRANT
    • REVOKE

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