CAST and CONVERT for type changes in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to convert the column 'price' to integer using CAST.

SQL

SELECT CAST(price AS [1]) FROM products;

Drag options to blanks, or click blank then click option'

AFLOAT

BDATE

CVARCHAR

DINT

Attempts:

3 left

💡 Hint

Common Mistakes

Using VARCHAR instead of INT causes the value to become text.

Using DATE or FLOAT changes the type incorrectly.

The CAST function changes the data type of 'price' to INT (integer).

2fill in blank

medium

Complete the code to convert the string '2023-01-01' to a DATE using CONVERT.

SQL

SELECT CONVERT([1], '2023-01-01', 23);

Drag options to blanks, or click blank then click option'

ADATE

BVARCHAR

CINT

DFLOAT

Attempts:

3 left

💡 Hint

Common Mistakes

Using VARCHAR keeps the value as text.

Using INT or FLOAT causes conversion errors.

CONVERT changes the string to a DATE type using style 23 (ISO format).

3fill in blank

hard

Fix the error in the code to convert '123.45' to integer using CAST.

SQL

SELECT CAST('123.45' AS [1]);

Drag options to blanks, or click blank then click option'

AVARCHAR

BINT

CFLOAT

DDATE

Attempts:

3 left

💡 Hint

Common Mistakes

Using FLOAT keeps the decimal and does not convert to integer.

Using VARCHAR does not convert to a number.

CAST to INT truncates the decimal part, converting '123.45' to 123.

4fill in blank

hard

Fill both blanks to convert the column 'birthdate' to VARCHAR with length 10 using CONVERT.

SQL

SELECT CONVERT([1]([2]), birthdate, 23) FROM users;

Drag options to blanks, or click blank then click option'

AVARCHAR

BINT

C10

DDATE

Attempts:

3 left

💡 Hint

Common Mistakes

Using INT as type causes errors.

Omitting length for VARCHAR causes syntax errors.

CONVERT to VARCHAR(10) formats the date as a string of length 10.

5fill in blank

hard

Fill all three blanks to cast the column 'amount' to FLOAT and then convert it to VARCHAR with length 8.

SQL

SELECT CONVERT([1]([2]), CAST(amount AS [3])) FROM sales;

Drag options to blanks, or click blank then click option'

AVARCHAR

B8

CFLOAT

DINT

Attempts:

3 left

💡 Hint

Common Mistakes

Using INT instead of FLOAT loses decimals.

Omitting length for VARCHAR causes errors.

First CAST 'amount' to FLOAT, then CONVERT it to VARCHAR(8) for string output.

Practice

1. What is the main purpose of using CAST or CONVERT in SQL?

easy

A. To change the data type of a value

B. To delete rows from a table

C. To create a new table

D. To join two tables

Solution

1. Step 1: Understand the function of CAST and CONVERT

   Both CAST and CONVERT are used to change the data type of a value in SQL.

2. Step 2: Compare with other options

   Deleting rows, creating tables, and joining tables are unrelated to changing data types.

3. Final Answer:

   To change the data type of a value -> Option A

4. Quick Check:

   CAST and CONVERT change types = A [OK]

Hint: CAST and CONVERT always change data types [OK]

Common Mistakes:

• Thinking CAST deletes data
• Confusing CONVERT with table creation
• Mixing data type change with joins

2. Which of the following is the correct syntax to convert a string '123' to an integer using CAST in SQL?

easy

A. CAST('123' AS INT)

B. CAST(INT AS '123')

C. CONVERT('123', INT)

D. CONVERT(INT, '123')

Solution

1. Step 1: Recall CAST syntax

   CAST requires the format CAST(value AS datatype), so CAST('123' AS INT) is correct.

2. Step 2: Check other options

   Options A, B, and D use incorrect order or syntax for CAST or CONVERT.

3. Final Answer:

   CAST('123' AS INT) -> Option A

4. Quick Check:

   CAST(value AS type) = C [OK]

Hint: CAST syntax is always CAST(value AS datatype) [OK]

Common Mistakes:

• Swapping value and datatype order
• Using CONVERT with wrong argument order
• Missing AS keyword in CAST

3. Given the SQL query:

SELECT CAST('2024-06-15' AS DATE) AS ConvertedDate;

What will be the output type of ConvertedDate?

medium

A. String

B. Boolean

C. Integer

D. Date

Solution

1. Step 1: Analyze the CAST operation

   The query casts the string '2024-06-15' to the DATE data type.

2. Step 2: Determine the output type

   Since CAST converts to DATE, the output column ConvertedDate will be of type Date.

3. Final Answer:

   Date -> Option D

4. Quick Check:

   CAST to DATE returns Date type = D [OK]

Hint: CAST to DATE returns a date type value [OK]

Common Mistakes:

• Assuming output stays string
• Confusing DATE with integer
• Thinking CAST changes value format only

4. Identify the error in this SQL statement:

SELECT CONVERT(INT, 'abc123');

medium

A. No error, converts string to integer

B. Syntax error due to wrong CONVERT argument order

C. Runtime error converting non-numeric string to INT

D. Missing AS keyword in CONVERT

Solution

1. Step 1: Check CONVERT syntax

   CONVERT(INT, 'abc123') is correct syntax in some SQL dialects like SQL Server.

2. Step 2: Consider conversion feasibility

   Trying to convert 'abc123' to INT causes a runtime error because 'abc123' is not numeric.

3. Final Answer:

   Runtime error converting non-numeric string to INT -> Option C

4. Quick Check:

   Non-numeric string to INT causes runtime error = A [OK]

Hint: Non-numeric strings cause errors when converting to INT [OK]

Common Mistakes:

• Assuming CONVERT always succeeds
• Confusing syntax error with runtime error
• Expecting implicit string to int conversion

5. You have a table Orders with a column OrderDate stored as VARCHAR in format 'YYYYMMDD'.
Which SQL query correctly converts OrderDate to a DATE type and selects orders from June 2024?

Options:
A) SELECT * FROM Orders WHERE CAST(OrderDate DATE) BETWEEN '2024-06-01' AND '2024-06-30';
B) SELECT * FROM Orders WHERE CONVERT(DATE, OrderDate, 112) BETWEEN '2024-06-01' AND '2024-06-30';
C) SELECT * FROM Orders WHERE CAST(OrderDate AS INT) BETWEEN 20240601 AND 20240630;
D) SELECT * FROM Orders WHERE CONVERT(INT, OrderDate) BETWEEN 20240601 AND 20240630;

hard

A. Option A only

B. Option B only

C. Option C only

D. Option D only

Solution

1. Step 1: Understand the data format and conversion

   OrderDate is VARCHAR in 'YYYYMMDD' format. CONVERT with style 112 converts this string correctly to DATE.

2. Step 2: Evaluate each option

   Option B only only tries CAST without style, which may fail or misinterpret format. Option B only only uses CONVERT with style 112, correct for 'YYYYMMDD'. Options C and D convert to INT, which is not reliable for date comparisons.

3. Final Answer:

   Option B only -> Option B

4. Quick Check:

   CONVERT with style 112 converts 'YYYYMMDD' to DATE = B [OK]

Hint: Use CONVERT with style 112 for 'YYYYMMDD' to DATE [OK]

Common Mistakes:

• Using CAST without format for 'YYYYMMDD'
• Converting dates to INT for comparison
• Ignoring CONVERT style parameter