Meaning: It is not possible to convert a null (i.e. empty value) type variable value into a double (double precision) type. This seems to be an error in data type conversion. This error often occurs when the report program does not handle fields with empty data. There will be no problem when there is data. When there is empty data, the program will report an error. Literally understood: the data type NULL cannot be converted into DOUBLE. There must be a problem when converting a certain field to DOUBLE. I checked the word tables one by one and found that the exchange rate is not defined. Click the currency with the mouse, right-click and select Association, enter the foreign exchange rate settings, and set the exchange rate for the corresponding currency. Try it again and this error will no longer appear.

Modify the property ADOConnection1.LoginPrompt:= False; I don’t know how you transfer the data. It may be that when you insert the data, there are no assigned non-null fields. Carefully check the corresponding field data. Unable to convert a variant of type (Null) to type (String). This tip says: You cannot convert a null value to a string type. You must perform a modify or insert operation. What system ado and Delphi ADO are the same thing. What is the reason for the incompatibility? Delphi only encapsulates ADO, but your mistake is obvious. There should be a program error. In this case, when the CX control counts the column, the data type of the column does not match the statistical method set in the summary. Solution: Change the footerformat value to blank and the footerkind value to sknone (if not, clear the attribute value)

It is a problem of the visual basic program not to convert the variant to a string. When writing a (cashier) program, the programmer does not type declare certain variables. By default, they are both used as variants. If the content of a variant is empty (null value), it cannot be converted to a string. There may be some things without content (name, barcode scan, etc.)

1. DBGrid can be modified, but at least two conditions are required:

1. The attribute settings of DBGrid itself allow users to modify it.

2. The data set component it is bound to can be modified.

2. The errors you mentioned:

1. The data set is not in edit or insert mode, which should belong to the second situation.

2. You need to set the data set component bound to DBGrid to edit mode.

Sample code if sender.value = null then text := '' else text := sender.value;