What implicit type conversions exist in mysql?

The implicit type conversions that exist in mysql include string to numeric types, date and time types, floating point and integer types, NULL values, etc. Detailed introduction: 1. Implicit type conversion from string to numeric type. When a string is compared or calculated with a value of numeric type, MySQL will convert the string into numeric type; 2. Implicit type conversion of date and time types. Implicit type conversion, in MySQL, date and time types can also perform implicit type conversion with other data types; 3. Implicit type conversion of floating point and integer types, etc.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

MySQL is an open source relational database management system that provides rich data types and powerful data processing functions. In MySQL, implicit type conversion means that when values ​​of different data types are used in an expression, MySQL automatically converts one data type to another data type for comparison, calculation, or other operations. In this article, we will discuss several common implicit type conversions that exist in MySQL.

1. Implicit type conversion from string to numeric type:

When a string is compared or calculated with a value of numeric type, MySQL will convert the string to a numeric type . For example, when a string is compared to an integer, MySQL converts the string to an integer type for comparison. If the string cannot be converted to a valid numeric type, MySQL will use 0 for conversion.

For example, assuming that the field age in a table is an integer type, we can execute the following query:

SELECT * FROM users WHERE age = '25';

Here, the string '25' will be implicitly converted to an integer type, so that Compare with age field.

2. Implicit type conversion of date and time types:

In MySQL, date and time types can also be implicitly type converted with other data types. For example, when a date or time type is compared to a string, MySQL converts the string to the date or time type.

For example, assuming that the field birthday in a table is of date type, we can execute the following query:

SELECT * FROM users WHERE birthday = '1990-01-01';

Here, the string '1990-01-01' will be implicitly converted to Date type for comparison with the birthday field.

3. Implicit type conversion between floating point numbers and integer types:

In MySQL, implicit type conversion between floating point numbers and integer types can also be performed. When a floating-point number is compared or calculated with an integer, MySQL converts the integer to a floating-point number.

For example, assuming that the field price in a table is of floating point type, we can execute the following query:

SELECT * FROM products WHERE price > 10;

Here, the integer value 10 will be implicitly converted to a floating point type, so that Compare with the price field.

4. Implicit type conversion of NULL values:

In MySQL, NULL values ​​can be compared or calculated with other data types. When a NULL value is operated on with other data types, MySQL implicitly converts the other data types to NULL values.

For example, assuming that the field quantity in a table is of integer type, we can execute the following query:

SELECT * FROM products WHERE quantity = NULL;

Here, the integer value quantity will be implicitly converted to a NULL value so that it can be used with NULL Compare.

Summary:

There are many types of implicit type conversions in MySQL, including string to numeric type conversion, date and time type conversion, floating point number and integer type conversion, and conversion of NULL values. These implicit type conversions can make us more flexible in data operations and calculations, but we also need to pay attention to the accuracy of the data type to avoid unexpected results. When developing and using MySQL databases, we should be familiar with these implicit type conversion rules in order to correctly handle data.

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