To select a column named 'FirstName' from a table named 'Persons' in SQL, you would use the SELECT statement. Let's go through each option to understand why it is correct or incorrect:

Option A) SELECT FirstName FROM Persons - This option is correct because it uses the SELECT statement to specify the column 'FirstName' that you want to retrieve from the table 'Persons'.

Option B) EXTRACT FirstName FROM Persons - This option is incorrect. The EXTRACT keyword is used to extract parts of a date or time value, not for selecting columns from a table.

Option C) SELECT Persons.FirstName - This option is incorrect. Although it specifies the desired column 'FirstName', it is missing the keyword FROM, which is necessary to indicate the table 'Persons' from which to retrieve the column.

Option D) SELECT * FROM Persons - This option is incorrect. The asterisk (*) symbol is used to select all columns from a table. It does not specifically select only the 'FirstName' column.

The correct answer is A) SELECT FirstName FROM Persons. This option is correct because it uses the SELECT statement to specify the 'FirstName' column from the 'Persons' table.

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To answer this question, you need to understand how to use the LIKE operator in SQL. The LIKE operator is used to search for a specified pattern in a column.

Let's go through each option to understand why it is correct or incorrect:

Option A) SELECT * FROM Persons WHERE FirstName LIKE 'a%' - This option is correct. The LIKE 'a%' condition will select all records from the 'Persons' table where the value of the 'FirstName' column starts with an 'a'.

Option B) SELECT * FROM Persons WHERE FirstName LIKE '%a' - This option is incorrect. The LIKE '%a' condition will select all records from the 'Persons' table where the value of the 'FirstName' column ends with an 'a', not starts with an 'a'.

Option C) SELECT * FROM Persons WHERE FirstName='a' - This option is incorrect. The = operator is used for exact matches. The condition FirstName='a' will select only the records where the value of the 'FirstName' column is exactly 'a', not those that start with an 'a'.

Option D) SELECT * FROM Persons WHERE FirstName='%a%' - This option is incorrect. The % wildcard character is used to match any sequence of characters. The condition FirstName='%a%' will select all records where the value of the 'FirstName' column contains an 'a' anywhere, not just at the beginning.

The correct answer is Option A) SELECT * FROM Persons WHERE FirstName LIKE 'a%'. This option is correct because it selects all records from the 'Persons' table where the value of the 'FirstName' column starts with an 'a'.

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To answer this question, you need to understand how to sort the result-set in SQL.

Option A) ORDER - This option is incorrect because the keyword "ORDER" alone is not used to sort the result-set. It needs to be combined with another keyword.

Option B) ORDER BY - This option is correct. The "ORDER BY" keyword is used in SQL to sort the result-set in ascending or descending order based on one or more columns.

Option C) SORT BY - This option is incorrect because "SORT BY" is not a valid keyword in SQL for sorting the result-set.

Option D) SORT - This option is incorrect because "SORT" is not a valid keyword in SQL for sorting the result-set.

The correct answer is B) ORDER BY. This option is correct because the "ORDER BY" keyword is used to sort the result-set in SQL.

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To answer this question, you need to understand the SUBSTRING function in SQL.

The SUBSTRING function is used to extract a substring from a given string. It takes three arguments: the input string, the starting position, and the length of the substring to be extracted.

In this case, the input string is '123456'. The starting position is 0, and the length is 3.

Using these arguments, the SUBSTRING function will extract a substring starting from the 0th position (which is the first character) with a length of 3 characters.

So, the output of the SUBSTRING('123456', 0, 3) statement will be '12'.

Therefore, the correct answer is B) 12.

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To answer this question, let's understand the function SUBSTRING() in SQL.

The SUBSTRING() function is used to extract a substring from a given string. It takes three parameters: the input string, the starting position of the substring, and the length of the substring.

In the given question, the input string is '123456', the starting position is 0, and the length of the substring is 3.

Using these parameters, the SUBSTRING() function will extract a substring from the input string starting at position 0 and with a length of 3.

Now, let's go through each option to determine the correct output:

Option A) 123 - This option is incorrect because the starting position is 0, which means the substring will start from the first character of the input string. Therefore, the output will not include the first character '1'.

Option B) 12 - This option is correct. The starting position is 0, so the substring will start from the first character '1'. The length of the substring is 3, so it will include the first two characters '1' and '2'.

Option C) 123456 - This option is incorrect because the length of the substring is 3. Therefore, the output will not include the entire input string.

Option D) 456 - This option is incorrect because the starting position is 0, so the substring will start from the first character '1'. The length of the substring is 3, so it will not include the characters '4', '5', and '6'.

The correct answer is Option B) 12. This option is correct because the substring will start from the first character '1' and have a length of 3, including the characters '1' and '2'.

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To answer this question, you need to understand the differences between the commands DROP, DELETE, and TRUNCATE in the context of deleting data from a table.

Option A) DROP - This option is incorrect because the DROP command is used to delete an entire table or database object, including its structure. It does not specifically delete data from a table without affecting the rollback segment.

Option B) DELETE - This option is incorrect because the DELETE command is used to delete specific rows from a table based on a condition. It does write to the rollback segment to allow for a rollback operation if needed.

Option C) TRUNCATE - This option is correct because the TRUNCATE command is used to delete all data from a table, but it does not write to the rollback segment. TRUNCATE is a DDL (Data Definition Language) command that is faster than DELETE because it deallocates the data pages and resets the highwater mark, freeing the space for reuse.

Option D) REMOVE - This option is incorrect because the REMOVE command is not a valid command in most database systems.

Option E) NONE OF THE ABOVE - This option is incorrect because option C (TRUNCATE) is the correct answer.

The correct answer is C) TRUNCATE. This option is correct because it deletes all data from a table without writing to the rollback segment.

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