Q.• Which of the two insert statement should be used when the order of data to be inserted are not known?
• Can we insert two records with the same roll number?
[Context: the two INSERT forms taught in the chapter are —

This is a plain theory question with two sub-parts about SQL INSERT syntax.

Which of the two insert statement should be used when the order of data to be inserted are not known?

When you do not know the order of columns in the table — or when you want to insert values in a different order from the table's definition — you must use the INSERT statement with explicit column names.

The syntax is:

INSERT INTO STUDENT (RollNumber, SName, SDateofBirth) 
VALUES (3, 'Taleem Shah', '2002-02-28');

Here you specify exactly which value goes into which column. The database matches each value to its named column, so the physical order of columns in the table does not matter. You can even rearrange the columns:

INSERT INTO STUDENT (SName, RollNumber, SDateofBirth) 
VALUES ('Taleem Shah', 3, '2002-02-28');

and the insertion will still be correct.

In contrast, the form without column names —

INSERT INTO STUDENT VALUES (3, 'Taleem Shah', '2002-02-28', NULL);

— requires you to supply values in the exact order the columns were defined when the table was created. If you do not know that order, or if the table structure changes later, this statement will either fail or insert data into the wrong columns.

Can we insert two records with the same roll number?

It depends on whether RollNumber is defined as a primary key or has a UNIQUE constraint. …

The Two Forms of INSERT

SQL offers two syntaxes for inserting rows:

1. Positional (implicit column order):

   INSERT INTO STUDENT VALUES (3, 'Taleem Shah', '2002-02-28', NULL);
   

   Values must appear in the exact order the columns were defined when the table was created. You must supply a value (or NULL) for every column.

2. Explicit column names:

   INSERT INTO STUDENT (RollNumber, SName, SDateofBirth) 
   VALUES (3, 'Taleem Shah', '2002-02-28');
   

   You list the columns you want to fill, in any order you choose, and provide values in the same order. Omitted columns receive their default value or NULL.

Question 1: Which form when column order is unknown?

If you don't know the physical order of columns in the table — perhaps the schema was created by someone else, or columns were added over time — the explicit column-name form is the only safe choice.

Why? The positional form blindly maps the first value to the first column, the second to the second, and so on. If you guess the order wrong, you might insert a name into a date field or a roll number into a text field, causing type errors or silent data corruption.

The explicit form lets you write

INSERT INTO STUDENT (SName, RollNumber, SDateofBirth) 
VALUES ('Taleem Shah', 3, '2002-02-28');

even if the table's actual column order is RollNumber, SName, SDateofBirth, …. The database matches each value to the column you named, regardless of physical position.

Question 2: Can we insert two records with the same roll number?

It depends on the table's constraints.

By default, SQL tables have no uniqueness requirement. You can insert

INSERT INTO STUDENT VALUES (3, 'Taleem Shah', '2002-02-28', NULL);
INSERT INTO STUDENT VALUES (3, 'Ananya Roy', '2003-05-15', NULL);

and both rows will be accepted. The table now contains two students with RollNumber = 3. …