Given the SQL expression:

What will be the result of executing this query?

Correct option is A

Let us break the query into its components for clarity:
Step 1: Understand the functions involved
INSTR Function:
· Syntax: INSTR(string, substring)
· Purpose: Finds the starting position of the first occurrence of the substring in the string (1-based indexing).
Input to INSTR:
· String: '0123456'
· Substring: '34'
Execution of INSTR:
· '34' starts at position 4 in '0123456'.
· So, INSTR('0123456', '34') evaluates to 4.
Step 2: Evaluate SUBSTR
SUBSTR Function:
· Syntax: SUBSTR(string, start_position, length)
· Purpose: Extracts a substring starting from start_position for length characters.
Input to SUBSTR:
· String: '0123456'
· Start Position: 4 (result of INSTR).
· Length: 4
Execution of SUBSTR:
· Starting at position 4 in '0123456', the substring of length 4 is extracted:
· Characters at positions:
· 4 → '3'
· 5 → '4'
· 6 → '5'
· 7 → '6'
· Extracted substring: '3456'.
Final Result:
· The result of the SQL query is '3456'.
Important Key Points:
· 1-Based Indexing: SQL string functions like INSTR and SUBSTR use 1-based indexing, meaning the first character is at position 1 (not 0, as in some programming languages).
· Always validate the inputs to avoid unexpected results, especially with functions that combine multiple operations like SUBSTR(INSTR(...)).
Knowledge Booster:
1. (b) '345': Incorrect, because the length specified is 4, and it correctly extracts 4 characters starting from position 4.
2. (c) '456': Incorrect, as the substring starts at position 4 and includes the character '3', making the result '3456'.
3. (d) Error: Incorrect, because both INSTR and SUBSTR handle valid inputs gracefully and do not raise errors.