MS SQL Server Indexes Question:
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Explain Having clause and Where clause?
Answer:
Having Clause: This clause is used for specifying a search condition for a group or an aggregate. It can only be used with a SELECT statement. It’s often used with GROUP BY clause without which its synonymous to a WHERE clause.
E.g.: SELECT Id, Name, Age FROM Customers
GROUP BY Age
HAVING Age>10
ORDER BYAge;
Where Clause: This clause is used to narrow down the dataset being dealt with following a condition.
SELECT Id, Name, Age FROM Customers
WHERE Age>10
It is strongly recommended to use a Where clause with every Select Statement to avoid a table scan and reduce the number of rows to be returned. It can be used with Select, Update, Delete etc statements.
E.g.: SELECT Id, Name, Age FROM Customers
GROUP BY Age
HAVING Age>10
ORDER BYAge;
Where Clause: This clause is used to narrow down the dataset being dealt with following a condition.
SELECT Id, Name, Age FROM Customers
WHERE Age>10
It is strongly recommended to use a Where clause with every Select Statement to avoid a table scan and reduce the number of rows to be returned. It can be used with Select, Update, Delete etc statements.
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