How to Improve Oracle SQL Queries Using 7 Best Practices

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When writing SQL queries, there is almost always more than one way to write the query to get the intended result. However, there are best practices that help with speed and efficiency. While there are many tips for writing SQL for Oracle, here is a short list of seven tips to help ensure a faster execution plan. 

  1.  Improve your queries. Rather than writing complex SQL statements that perform multiple tasks, write a separate statement for each individual task. 
  2.  Use Table Aliases. Another way to improve your queries is to use Table Aliases. Table Aliases are generally short abbreviations used in place of the full table name. Here is an example of a query without a table alias.

SELECT product . *

FROM product

INNER JOIN status_lookup  ON  product . status  =  status_lookup .status

WHERE status_lookup . category  =  ‘ACTIVE’ ;

Here is another example of the same query using a table alias.

SELECT p . *

FROM product p

INNER JOIN status_lookup  s  ON  p . status  =  s .status

WHERE s . category  =  ‘ACTIVE’ ;

Table aliases make the query easier to read and write.

  1. Do not use object names with spaces. Object names that use spaces, which may seem to make the name easier to read, may cause issues, and are also inconvenient to use. Using underscores in a space can make the table just as easy to read without causing as much of an inconvenience.

  2. Use the UNION ALL operator. If you need to write a complex statement, use UNION ALL rather than UNION to reduce the number of steps performed. Use the minus operator instead of using EXISTS. 

  3. Minimize the use of DISTINCT. While adding a DISTINCT keyword will prevent duplicate results, it may also slow down your query. Instead, it may be best to fix the issue that is causing the duplicate row.

  4. Try not to use Group Filters. Because the process of removing records retrieved by your query occurs in the middle tier, the best practice is to use the WHERE clause conditions, which occur at the database level—using WHERE is more efficient.

  5. Use NOT EXISTS. Using NOT EXISTS instead of using NOT IN or HAVING will result in a faster search.

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