Converting Data Types in DB2 (Using CAST and CONVERT Functions)

Data Type Conversion in db2 Database

In the DB2 database, using CAST and CONVERT functions for data type conversion is very common.

1. Using CAST Function for Data Type Conversion

The CAST function is used to convert the value of an expression into another data type. Below is the basic syntax of the CAST function:

CAST(表达式 AS 数据类型)

For example, using the CAST function to convert a number to string type can be written as follows:

SELECT CAST('123' AS VARCHAR) FROM DUAL;

2. Using CONVERT Function for Data Type Conversion

The CONVERT function is used to convert a value into a specified data type. Below is the basic syntax of the CONVERT function:

CONVERT(数据类型 FROM 表达式)

For example, using the CONVERT function to convert a date to time type can be written as follows:

SELECT CONVERT(DATE FROM '2022-01-01 12:00:00') AS date;

3. Using CAST and CONVERT Functions Together for Data Type Conversion

The CAST and CONVERT functions can also be used together in data type conversion. Below is the combined syntax of the CAST and CONVERT functions:

CAST(表达式 AS 数据类型) Convert（数据类型 FROM 表达式）

For example, using the CAST and CONVERT functions to convert a date to time type can be written as follows:

SELECT CAST('2022-01-01 12:00:00' AS DATE) CONVERT (TIME FROM '2022-01-01 12:00:00');

4. Using CAST and CONVERT Functions for Data Type Conversion of NULL Values

The CAST and CONVERT functions can also be used to handle data type conversion of NULL values. Below is the syntax for using the CAST and CONVERT functions to convert NULL values:

IF NULL THEN CAST(表达式 AS 数据类型) ELSE 表达式 END IF

For example, using the CAST and CONVERT functions to perform data type conversion on NULL values can be written as follows:

SELECT IF NULL THEN CAST('123' AS VARCHAR) ELSE '456' END IF;

5. Using CAST and CONVERT Functions for Data Type Conversion of Empty Strings

The CAST and CONVERT functions can also be used to handle data type conversion of empty strings. Below is the syntax for using the CAST and CONVERT functions to convert empty strings:

IF NULL THEN CAST(表达式 AS 数据类型) ELSE '' END IF

For example, using the CAST and CONVERT functions to perform data type conversion on empty strings can be written as follows:

SELECT IF NULL THEN CAST('123' AS VARCHAR) ELSE '' END IF;

6. Using CAST and CONVERT Functions for Data Type Conversion of Empty Values

The CAST and CONVERT functions can also be used to handle data type conversion of empty values. Below is the syntax for using the CAST and CONVERT functions to convert empty values:

IF NULL THEN CAST(表达式 AS 数据类型) ELSE NULL END IF

For example, using the CAST and CONVERT functions to perform data type conversion on empty values can be written as follows:

SELECT IF NULL THEN CAST('123' AS VARCHAR) ELSE NULL END IF;

7. Using CAST and CONVERT Functions for Data Type Conversion of NaN Values

The CAST and CONVERT functions can also be used to handle data type conversion of NaN values. Below is the syntax for using the CAST and CONVERT functions to convert NaN values:

IF NULL THEN CAST(表达式 AS 数据类型) ELSE NaN END IF

For example, using the CAST and CONVERT functions to perform data type conversion on NaN values can be written as follows:

SELECT IF NULL THEN CAST('123' AS FLOAT) ELSE NaN END IF;

8. Using CAST and CONVERT Functions for Data Type Conversion of Infinity Values

The CAST and CONVERT functions can also be used to handle data type conversion of Infinity values. Below is the syntax for using the CAST and CONVERT functions to convert Infinity values:

IF NULL THEN CAST(表达式 AS 数据类型) ELSE INF END IF

For example, using the CAST and CONVERT functions to perform data type conversion on Infinity values can be written as follows:

SELECT IF NULL THEN CAST('123' AS FLOAT) ELSE INF END IF;

9. Using CAST and CONVERT Functions for Data Type Conversion of MAX Values

The CAST and CONVERT functions can also be used to handle data type conversion of MAX values. Below is the syntax for using the CAST and CONVERT functions to convert MAX values:

IF NULL THEN CAST(表达式 AS 数据类型) ELSE MAX END IF

For example, using the CAST and CONVERT functions to perform data type conversion on MAX values can be written as follows:

SELECT IF NULL THEN CAST('123' AS FLOAT) ELSE MAX END IF;

10. Using CAST and CONVERT Functions for Data Type Conversion of MIN Values

The CAST and CONVERT functions can also be used to handle data type conversion of MIN values. Below is the syntax for using the CAST and CONVERT functions to convert MIN values:

IF NULL THEN CAST(表达式 AS 数据类型) ELSE MIN END IF

For example, using the CAST and CONVERT functions to perform data type conversion on MIN values can be written as follows:

SELECT IF NULL THEN CAST('123' AS FLOAT) ELSE MIN END IF;