Several common data type conversion functions in MySQL

MySQL database is a commonly used relational database software, which is widely used in applications of all sizes. In the MySQL database, type conversion of data is often required. Among them, the most common type conversion is to convert a data type into an integer.

In the MySQL database, it is often necessary to use integer data for calculations, sorting and other operations. In order to ensure the correctness and validity of the data, we need to convert other data types into integers. MySQL provides some functions to convert other data types into integers. Below, we will introduce several common data type conversion functions and their application methods in MySQL:

1. CAST() function

CAST(expr AS type) function can Convert the type of expression expr to type type. This function can be used with any data type supported by MySQL.

Example:

Convert string type to integer type:

SELECT CAST('123' AS signed);

Execute the above statement, the output result is:

+----------------+
| CAST('123' AS signed) |
+----------------+
|              123 |
+----------------+

In the above example, the string type "123" is converted into an integer type. Among them, "signed" is a type of integer in MySQL and can be replaced by keywords such as "unsigned" and "blob". This function can be used in various type conversions and has good versatility.

2. CONVERT() function

CONVERT(expr,type) function can also convert the data type from expr to type. This function is similar to the CAST() function in usage, but differs in some details.

Example:

Convert string type to integer type:

SELECT CONVERT('123', signed);

Execute the above statement, the output result is:

+-----------------------+
| CONVERT('123', signed) |
+-----------------------+
|                   123 |
+-----------------------+

In the above example, the string type "123" is converted into an integer type. Among them, "signed" is also a type of integer in MySQL, and is used here as an indicator.

3. SIGNED() function

SIGNED(expr) function can convert the expression expr to a signed integer. If expr is a string type, it will be parsed as an integer. If it cannot be parsed into an integer, 0 is returned.

Example:

Convert string type to integer type:

SELECT SIGNED('123');

Execute The output result of the above statement is:

+---------------+
| SIGNED('123') |
+---------------+
|           123 |
+---------------+

In the above example, the string type "123" is converted into an integer type.

4. UNSIGNED() function

UNSIGNED(expr) function can convert the expression expr to an unsigned integer. If expr is a string type, it will be parsed as an integer. If it cannot be parsed into an integer, 0 is returned.

Example:

Convert string type to integer type:

SELECT UNSIGNED('123');

Execute The output result of the above statement is:

+-----------------+
| UNSIGNED('123') |
+-----------------+
|             123 |
+-----------------+

In the above example, the string type "123" is converted into an integer type.

Summary:

In the MySQL database, type conversion operations are often required. The Cast(), convert(), signed() and unsigned() functions are the most commonly used data type conversion functions in MySQL, which can help us easily convert a data type into an integer. According to different actual situations, we can choose the type conversion function that suits us to meet our needs. For some data type conversion errors, we need to use conditional judgment functions such as if() in SQL statements to handle them.

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