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DDL and DML Commands

DML statements are SQL statements that manipulate data. DML stands for Data Manipulation Language. The SQL statements that are in the DML class are INSERT, UPDATE and DELETE. Some people also lump the SELECT statement in the DML classification.

Data Definition Languages (DDL) are used to define the database structure. Any CREATE, DROP and ALTER commands are examples of DDL SQL statements.

Aggregate Functions are all about

  • Performing  calculations on multiple rows
  • Of a single column of a table
  • And returning a single value.

The ISO standard defines five (5) aggregate functions namely;

1) COUNT
2) SUM
3) AVG
4) MIN
5) MAX 

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