_FAQ For SQL

What is the difference between the HAVING clause and the WHERE?

• The WHERE clause used to filter individual rows before they are grouped together, while HAVING is used to filter groups after they are created by a GROUP BY clause.
  
  
• i.e., HAVING applies to the entire group of tuple, partitioned by the GROUP BY clause.
  
  

Clause vs Keyword vs Statement?

• Statement: A complete SQL command to perform a specific task (e.g., querying, updating data, inserting data). Uses a combination of clauses and keywords.
  
  
• Clause: a clause is a part of a SQL statement that provides additional information about the operation being performed (e.g., WHERE, GROUP BY, HAVING, ORDER BY).
  
  
• Keyword: A keyword is a reserved word in SQL that has a specific meaning and purpose in the programming language.
  
  

What is the different between ASSERTION and CHECK?

• The CHECK constraint is used to enforce domain integrity by limiting the values that can be inserted into a column or a set of columns in a table. It is used to ensure that only valid data is entered into the table.
  
  
• While the CHECK constraint is used to enforce simple constraints on individual columns or sets of columns, the ASSERTION is used to enforce more complex constraints that involve multiple tables or multiple rows.