mysql string type conversion

MySQL is a widely used relational database management system that supports a variety of data types. Among them, the string type is a very common one. In daily database operations, it is sometimes necessary to convert string types. This article will introduce the commonly used string type conversion operations in MySQL.

1. CAST and CONVERT functions

The CAST and CONVERT functions convert one data type to another. Their syntax is very similar, but some details differ. For example:

CAST(expression AS type)

CONVERT(expression,type)

where expression is the expression or column to be converted, and type is the expression that needs to be converted to The target data type. For example:

SELECT CAST('123' AS UNSIGNED);

SELECT CONVERT('123',UNSIGNED);

The two statements have the same effect. Both convert the string '123' into an unsigned integer type.

2. Conversion between various string types

MySQL supports multiple string types. Here are some common conversion methods between types:

2.1 Convert string type to date and time type

DATE, TIME, DATETIME types are very convenient for the storage and operation of date and time. We can use the STR_TO_DATE function to convert a string into date or time type.

For example:

SELECT STR_TO_DATE('2022-01-01','%Y-%m-%d');

The function of this statement is to convert the characters The string '2022-01-01' is converted into DATE type.

2.2 Convert string type to enumeration type

The enumeration type is a MySQL-specific type that is suitable for some fixed value ranges.

We can use the ENUM function to convert the string type into an enumeration type:

SELECT ENUM('green','red','blue');

This The function of the statement is to convert the string 'green' into an enumeration type, which is commonly used to store fixed options such as gender and country.

2.3 Convert string type to binary type

Binary type is suitable for storing binary data, such as pictures, audio, etc.

We can use the HEX function to convert a string into a hexadecimal type to achieve conversion from a string to a binary type. For example:

SELECT HEX('abc');

The function of this statement is to convert the string 'abc' into hexadecimal type representation.

3. Common errors and solutions

During the string type conversion process, some errors often occur. Here is a brief introduction to some common errors and their solutions.

3.1 The string contains non-numeric characters

When the string contains non-numeric characters, an error will be reported when using the CAST and CONVERT functions to convert the string into a numeric type. You can use the function TRIM to remove spaces from a string, and the function REPLACE to replace non-numeric characters with null characters.

For example:

SELECT CAST(REPLACE(TRIM(' 123abc '),' ','')AS UNSIGNED);

The function of this statement is to convert the string ' 123abc ' Convert to unsigned integer type.

3.2 The date or time format does not meet the requirements

The format of the date or time type must meet the requirements of MySQL, otherwise an error will be reported. You can use the function STR_TO_DATE to convert a string type to a target date or time type, specifying the correct format.

For example:

SELECT STR_TO_DATE('20220101', '%Y%m%d');

The function of this statement is to convert the string '20220101' into Date type.

Through the introduction of this article, we have learned about the common methods and error handling methods of string type conversion in MySQL. These functions can help us quickly and efficiently complete string type conversion operations and improve the efficiency of database operations.

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