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What is the purpose of the where clause in a query?

What is the purpose of the where clause in a query?

The SQL WHERE clause is used to specify a condition while fetching the data from a single table or by joining with multiple tables. If the given condition is satisfied, then only it returns a specific value from the table. You should use the WHERE clause to filter the records and fetching only the necessary records.

Does where clause improve performance?

A where clause will generally increase the performance of the database.

  • Generally, it is more expensive to return data and filter in the application.
  • The database can optimize the query, using indexes and partitions.
  • The database may be running in parallel, executing the query in parallel.

What is the purpose of the where clause in and SQL retrieval query?

The WHERE clause is used to constrain which rows to retrieve. We do this by specifying a boolean predicate that compares the values of table columns to literal values or to other columns. The ORDER BY clause gives us a way to order the display of the rows in the result of the statement.

Can you write a query without using the where clause?

In a SELECT statement, WHERE clause is optional. Using SELECT without a WHERE clause is useful for browsing data from tables. In a WHERE clause, you can specify a search condition (logical expression) that has one or more conditions.

What is Commission_pct?

The Oracle function NVL(expression, value) converts any NULL values found in the expression to a value specified. You then compare the column commission_pct of every record returned which had a NULL value to the value 0 .

What is the benefit of where clause in DBMS?

WHERE clauses are not mandatory clauses of SQL DML statements, but can be used to limit the number of rows affected by a SQL DML statement or returned by a query. In brief SQL WHERE clause is used to extract only those results from a SQL statement, such as: SELECT, INSERT, UPDATE, or DELETE statement.

What are the alter commands?

alter command is used for altering the table structure, such as,

  • to add a column to existing table.
  • to rename any existing column.
  • to change datatype of any column or to modify its size.
  • to drop a column from the table.

What is the use of order by clause?

An ORDER BY clause in SQL specifies that a SQL SELECT statement returns a result set with the rows being sorted by the values of one or more columns. The sort criteria do not have to be included in the result set.

What is the difference between having and where clause?

WHERE Clause is used to filter the records from the table based on the specified condition. HAVING Clause is used to filter record from the groups based on the specified condition.

What is the having clause?

A HAVING clause in SQL specifies that an SQL SELECT statement must only return rows where aggregate values meet the specified conditions. To view the present condition formed by the GROUP BY clause, the HAVING clause is used.

How use having in SQL query?

The Having clause in a Select Statement without a GROUP BY clause: select * from employee HAVING EmpID=1….The following SQL query shows a Having with an Order By clause:

  1. select EmpName, SUM(EmpSalary) as EmpSalary from Employee.
  2. GROUP BY EmpName.
  3. HAVING SUM(EmpSalary) < 30000.
  4. order by EmpName desc.

What is faster inner join or where clause?

10 Answers. Theoretically, no, it shouldn’t be any faster. The query optimizer should be able to generate an identical execution plan. However, some database engines can produce better execution plans for one of them (not likely to happen for such a simple query but for complex enough ones).

Which join is most efficient?

TLDR: The most efficient join is also the simplest join, ‘Relational Algebra’.

Are inner joins faster than left joins?

A LEFT JOIN is absolutely not faster than an INNER JOIN . In fact, it’s slower; by definition, an outer join ( LEFT JOIN or RIGHT JOIN ) has to do all the work of an INNER JOIN plus the extra work of null-extending the results.

Why are Joins slow?

Further most people who denormalize because “joins are slow” don’t know enough about databases to properly make sure their data integrity is protected and often end up with databases that have unuseable data becasue the integrity is so bad.

Does primary key improve performance?

By itself, a primary key does not have a direct affect on performance. But indirectly, it does. This is because when you add a primary key to a table, SQL Server creates a unique index (clustered by default) that is used to enforce entity integrity.

Is view faster than query MySQL?

No, a view is simply a stored text query. You can apply WHERE and ORDER against it, the execution plan will be calculated with those clauses taken into consideration.

How can I speed up my database query?

Below are 23 rules to make your SQL faster and more efficient

  1. Batch data deletion and updates.
  2. Use automatic partitioning SQL server features.
  3. Convert scalar functions into table-valued functions.
  4. Instead of UPDATE, use CASE.
  5. Reduce nested views to reduce lags.
  6. Data pre-staging.
  7. Use temp tables.
  8. Avoid using re-use code.