SQL Queries you can run and test in your project to update or modify existing rows in a Table.
These are best practices and guide lines to review any SQL program. The example given here is for COBOL.
Index and Key both are different in RDBMS. Take a look all these differences quickly
Top differences between stored procedures and functions you can read and refresh quickly. Good summary for SQL developers.
Do review your SQL query program before put it into application program with these ideas. Read more.
Multiple nested query and Correlated sub-query both are different. Try to understand these with examples…