How to Correctly Apply WHERE Clause Filtering in Complex SQL Queries?

Priority issue of WHERE parameter in SQL statement

The following SQL query is designed to retrieve data from the "people" table and limit the results to records with "university=2":

<code class="language-sql">SELECT * FROM people 
WHERE
university='2' 
AND MATCH (lname,fname) AGAINST ('+massive' IN BOOLEAN MODE) 
OR (fname LIKE '%box%' OR lname LIKE '%box%') </code>

However, this query produced unexpected results beyond the "university=2" condition. To solve this problem, we need to ensure that the "university=2" condition strictly limits the search results.

Adjust brackets to control the order of operations

The problem with this query is the improper use of parentheses, which affects the order of evaluation of the expression. In the original query, "AND" has a higher priority than "OR", which means it is evaluated first. As a result, "university=2" is only combined with "MATCH (lname,fname) AGAINST (' massive' IN BOOLEAN MODE)" and not with the "fname/lname" test.

To correct this, we need to adjust the brackets to ensure that "university=2" is combined with the entire search criteria:

<code class="language-sql">SELECT * FROM people 
WHERE
    university='2' 
    AND (MATCH (lname,fname) AGAINST ('+massive' IN BOOLEAN MODE) 
         OR fname LIKE '%box%' 
         OR lname LIKE '%box%') </code>

With this adjustment, the "university=2" condition is now enclosed in parentheses, indicating that it should be evaluated first and then combined with the search conditions within the second set of parentheses. This ensures that only records where "university=2" is true will be considered in the search.

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