Tag: sql

Questions Related to sql

Given an employees table as follows: empid name managerid a1 bob NULL b1 jim a1 B2 tom a1 What value will select count(*) from employees return?
sql

  1. 1

  2. 2

  3. 3

  4. none of the above

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Correct Option: C

The result of a SELECT statement can contain duplicate rows.

sql

  1. True

  2. False

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Correct Option: A

Sometimes the expression "select count(*)" will return fewer rows than the expression "select count(value)".

sql

  1. True

  2. False

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Correct Option: B
Explanation:

To solve this question, one needs to understand the difference between count(*) and count(column_name).

count(*) returns the total number of rows in the table, whereas count(column_name) returns the number of non-null values for the given column.

Now, let's go through each option and explain why it is right or wrong:

A. True: This option is false. count(*) will always return the same value as the number of rows in the table, while count(column_name) will return the number of non-null values for the given column. Thus, it is possible for count(column_name) to return a higher value than count(*), but not a lower value.

B. False: This option is correct. count(*) returns the total number of rows in the table, whereas count(column_name) returns the number of non-null values for the given column. Thus, it is not possible for count(column_name) to return fewer rows than count(*).

The Answer is: B

What type of lock will deny users any access to a table?

sql

  1. EXPLICIT

  2. IMPLICIT

  3. EXCLUSIVE

  4. SHARED

  5. READ ONLY

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Correct Option: C

Which of the following is the correct SQL statement to use to remove rows from a table?

sql

  1. DROP

  2. REMOVE ROW

  3. DELETE

  4. DELETE ROW

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Correct Option: C

AI Explanation

To remove rows from a table in SQL, the correct statement to use is the DELETE statement. Let's go through each option to understand why it is correct or incorrect:

Option A) DROP - The DROP statement is used to delete an entire table or database, not specific rows within a table. Therefore, this option is incorrect.

Option B) REMOVE ROW - There is no specific SQL statement called REMOVE ROW. Therefore, this option is incorrect.

Option C) DELETE - The DELETE statement is used to remove one or more rows from a table based on a specific condition. It allows you to specify a WHERE clause to determine which rows should be deleted. This is the correct statement to use for removing rows from a table. Therefore, this option is correct.

Option D) DELETE ROW - There is no specific SQL statement called DELETE ROW. Therefore, this option is incorrect.

The correct answer is C) DELETE. This option is correct because the DELETE statement is used to remove one or more rows from a table based on a specific condition.

The only way to join two tables is by using standard, ANSI syntax.

sql

  1. True

  2. False

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Correct Option: B

AI Explanation

To answer this question, you need to understand the different ways to join tables in SQL.

Option A) True - This option is incorrect because there are multiple ways to join tables in SQL, not just by using standard ANSI syntax. Other join types include INNER JOIN, OUTER JOIN (LEFT, RIGHT, FULL), CROSS JOIN, etc.

Option B) False - This option is correct because it acknowledges that the only way to join two tables is not limited to standard ANSI syntax. SQL provides various join types and syntax options to join tables based on the specific requirements of the query.

The correct answer is B) False. This option is correct because there are multiple ways to join tables in SQL, not just by using standard ANSI syntax.

A NULL value is treated as a blank or 0.

sql

  1. True

  2. False

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Correct Option: B
Explanation:

To solve this question, the user needs to know the concept of NULL value and its treatment in programming.

The correct answer is:

B. False

Explanation:

In programming, a NULL value represents the absence of a value or an unknown value. It is not the same as a blank or 0. When a variable is assigned a NULL value, it means that no value has been assigned to it or that the value is unknown.

In SQL, for example, NULL values cannot be compared using the equality operator (=) or inequality operator (<>). Instead, you have to use the IS NULL or IS NOT NULL operator to check for NULL values.

Therefore, option B is the correct answer as a NULL value is not treated as a blank or 0.

The left outer join is one type of outer join. Another one is the.
sql

  1. right

  2. full

  3. right outer

  4. full outer

  5. all of the above

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Correct Option: E

What will be the output of the following statement? SELECT LEN(CAST(LEFT('026-100', 3) AS INT))
sql

  1. 2

  2. 3

  3. 7

  4. Statement will generate an error.

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Correct Option: A
Explanation:

To solve this question, the user needs to know that the LEFT function extracts a specified number of characters from the left side of a given string. The CAST function converts a given expression to a specified data type. The LEN function returns the number of characters in a given string.

In this case, the LEFT function is extracting the first three characters from the string '026-100', which results in '026'. The CAST function is converting this string to an integer data type, resulting in the value 26. The LEN function then determines the number of characters in the resulting string, which is 2. Therefore, the correct answer is:

The Answer is: B. 2

What will be the output of the following statement? SELECT CAST(-1 AS SMALLDATETIME)
sql

  1. 1900-01-01 00:00:00.000

  2. 1899-01-01 00:00:00.000

  3. 1752-01-01 00:00:00.000

  4. The system will generate an error. Only positive integer values can be converted to a SMALLDATETIME data type.

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Correct Option: D
Explanation:

To solve this question, the user needs to know about the SMALLDATETIME data type and how to cast values to it.

In SQL Server, SMALLDATETIME is a data type that stores a date and time with a precision of one minute. It is represented as a two-byte signed integer.

The CAST function is used to convert one data type to another. In this case, the value -1 is being cast to the SMALLDATETIME data type.

Now, let's go through each option and explain why it is right or wrong:

A. 1900-01-01 00:00:00.000: This option is incorrect because the SMALLDATETIME data type has a minimum value of 1900-01-01 00:00:00. The value -1 is less than the minimum value, so it cannot be converted to a SMALLDATETIME.

B. 1899-01-01 00:00:00.000: This option is incorrect because the SMALLDATETIME data type has a minimum value of 1900-01-01 00:00:00. The value -1 is less than the minimum value, so it cannot be converted to a SMALLDATETIME.

C. 1752-01-01 00:00:00.000: This option is incorrect because the SMALLDATETIME data type has a minimum value of 1900-01-01 00:00:00. The value -1 is less than the minimum value, so it cannot be converted to a SMALLDATETIME.

D. The system will generate an error. Only positive integer values can be converted to a SMALLDATETIME data type: This option is incorrect because the SMALLDATETIME data type can store both positive and negative integer values. However, the value -1 is less than the minimum value of the SMALLDATETIME data type, so it cannot be converted to a SMALLDATETIME.

The Answer is: D