How can I convert 12-hour time to 24-hour time in an SQL server for the entire table?

 To convert a 12-hour time format (with AM/PM) to a 24-hour time format in SQL Server for an entire table, you can use the CONVERT or CAST function along with the appropriate format.

Here’s an example SQL query to convert a column from 12-hour to 24-hour format for all rows in the table:

Steps:

1. Assume you have a column named Time12Hour in a table MyTable which stores the time in a 12-hour format with an AM/PM indicator.
2. Use the CONVERT function to convert the time string from 12-hour format to 24-hour format.

Here is the SQL query:

SELECT 
    Time12Hour, 
    CONVERT(VARCHAR, CAST(Time12Hour AS DATETIME), 108) AS Time24Hour
FROM MyTable;

Explanation:

• CAST(Time12Hour AS DATETIME): Converts the 12-hour formatted time into a DATETIME type. SQL Server automatically interprets the 12-hour time format correctly (e.g., 08:30 PM will be interpreted as 20:30).
• CONVERT(VARCHAR, ..., 108): Converts the DATETIME value to a string in 24-hour format (108 is the style code for HH:mm:ss format).

Example:

If your MyTable looks like this:

Time12Hour
08:30 AM
02:45 PM
11:59 PM

Running the query would produce:

Time12Hour	Time24Hour
08:30 AM	08:30:00
02:45 PM	14:45:00
11:59 PM	23:59:00

Updating the Entire Table:

If you want to update the Time12Hour column in your table to store the times in 24-hour format, you can use the following UPDATE query:

UPDATE MyTable
SET Time12Hour = CONVERT(VARCHAR, CAST(Time12Hour AS DATETIME), 108);

This will overwrite the Time12Hour column with the new 24-hour formatted time values.

Important Notes:

• This method assumes the Time12Hour column is stored as a string in a recognizable 12-hour format (e.g., 'hh:mm tt' where tt is AM or PM).
• If your time data is in a different format (such as HH:mm:ss), you would adjust the conversion accordingly.