Type casting and conversion in MySQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is type casting in MySQL?

Type casting in MySQL means changing a value from one data type to another, like turning a string into a number or a number into a string.

beginner

How do you convert a string to an integer in MySQL?

You can use the CAST() function like this: CAST('123' AS UNSIGNED) to convert the string '123' to the number 123.

intermediate

What does the CONVERT() function do in MySQL?

CONVERT() changes a value from one type to another, similar to CAST(), for example CONVERT('2023-01-01', DATE) converts a string to a date.

intermediate

What happens if you cast a non-numeric string to a number in MySQL?

MySQL converts the string to 0 if it cannot find a valid number at the start of the string.

beginner

Why is type casting useful in SQL queries?

It helps compare or calculate values correctly when they are stored as different types, like comparing a number stored as text with a real number.

Which MySQL function converts a value to a different data type?

A ALTER()

B CHANGE()

C MODIFY()

D CAST()

CAST() is used to convert a value from one data type to another.

What is the result of CAST('abc' AS UNSIGNED) in MySQL?

A 0

B abc

C NULL

D Error

Non-numeric strings cast to numbers become 0 in MySQL.

How do you convert a string '2023-06-01' to a DATE type in MySQL?

A DATE('2023-06-01')

B CAST('2023-06-01' AS DATE)

C TO_DATE('2023-06-01')

D CONVERT('2023-06-01' TO DATE)

CAST('2023-06-01' AS DATE) correctly converts the string to a DATE.

Which data type would you cast to if you want a decimal number?

A DECIMAL

B CHAR

C DATE

D BLOB

DECIMAL is used for precise decimal numbers.

What does CONVERT('123', UNSIGNED) do in MySQL?

A Returns string '123' unchanged

B Changes string to uppercase

C Converts string '123' to number 123

D Throws an error

CONVERT('123', UNSIGNED) changes the string to the number 123.

Explain how to convert a string to a number in MySQL and what happens if the string is not numeric.

Think about how MySQL handles strings that don't start with digits.

Describe why type casting is important when working with different data types in SQL queries.

Consider what happens if you compare a number stored as text with a real number.