When writing SQL statements with multiple conditions in the WHERE clause, it's important to understand how logical operators like AND and OR work. These operators are used to filter records based on more than one condition:
The AND operator displays a record if all the conditions separated by AND are TRUE.
The OR operator displays a record if any of the conditions separated by OR is TRUE.
The precedence of these operators is also important: AND operations are always evaluated before OR operations unless parentheses are used to explicitly define the order of operations. Therefore, conditions enclosed in parentheses are evaluated first as per the standard SQL operator precedence.
Given this understanding, let's evaluate the options:
Option A uses parentheses to group the borrowed_date and transaction_type conditions together, ensuring these are evaluated first before the OR operator. This means the query will return records that meet both of these conditions or records with member_id 'A101' or 'A102', regardless of other conditions.
Option D does not use parentheses around the borrowed_date and transaction_type conditions but does use them to group the member_id conditions. Since the AND operator has higher precedence than the OR, this query will first evaluate the borrowed_date and transaction_type conditions, then evaluate the grouped member_id conditions. The outcome is records that have a borrowed_date of SYSDATE, a transaction_type of 'RM', and a member_id of either 'A101' or 'A102'.
The results of Options A and D are effectively the same, even though the use of parentheses is different. This is because in both cases, the evaluation of the borrowed_date and transaction_type conditions will be performed first due to their grouping by parentheses in Option A and the precedence of AND over OR in Option D. Therefore, they will both return all records where borrowed_date equals SYSDATE and transaction_type equals 'RM', plus any records where member_id is either 'A101' or 'A102'.
For further details on SQL operator precedence and logical operators, you can refer to Oracle Database SQL Language Reference 12c documentation, specifically the sections on conditional expressions.
