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Add a column to db-tables

Posted on 1998-05-25
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Last Modified: 2010-04-06
I a couple of tables and have to add another Column to the existing table, and then save the table with the new Column, how do I do that, btw I'm using Delphi 2.0.
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Question by:koger
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Expert Comment

by:jturpin
ID: 1347738
The best way to do that is by using the
"Borland Database Desktop" under "Tools"
(I think) on the main Delphi2 menu.

John.
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Author Comment

by:koger
ID: 1347739
Ehh, well, I need to create a program that can add a column, so what I need is some code ;-)
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Expert Comment

by:jturpin
ID: 1347740
Ok you seem to have missed that point in
your original question.

I don't believe you can simply add a column
to a table. I usually clone the structure
of the original table, add the column, and then
select the info I need. But you could try
simply adding the column to the existing table
if you want, although I think you will get
an error.

The code for adding a column to the table is:

   OriginalTable.FieldDefs.Add(FieldName,
      FieldType,FieldLen,false);

   e.g.
      Table1.FieldDefs.Add('SupCarry',ftString,SupLEN,false);
      Table1.FieldDefs.Add('PayCarAll',ftBoolean,0,false);
      Table1.FieldDefs.Add('Rate',ftFloat,0,false);
      Table1.Exclusive:= true;
   
      Table1.CreateTable;

I hope that helps,

John.
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Author Comment

by:koger
ID: 1347741
To jturpin

Here is a ex. of the code I use:

Table1.FieldDefs.Add('NewEntry:', ftString, 25, False);
Table1.CreateTable;

This will causs all the existing information in the table to be erased :-(, how is it possible to keep the existing information and still add an extra column?
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Expert Comment

by:ronit051397
ID: 1347742
Use SQL. For adding a new field, called 'TEST' to the ANIMALS table write:

with Query1 do
begin
  DatabaseName:='DBDEMOS';
  SQL.Text:='ALTER TABLE "ANIMALS.dbf" ADD TEST SMALLINT';
  ExecSQL;
end;

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Author Comment

by:koger
ID: 1347743
It must be possible to add a column, without using SQL.
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Expert Comment

by:BlackMan
ID: 1347744
You need to use the dbiDoRestructor procedure. There is an example at http://www.inprise.com/devsupport/bde/bdeapiex/dbidorestructure.html
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Author Comment

by:koger
ID: 1347745
Ok I have tried it all, and I simply don't get it, so I will take it one more time

I have to add a column to a paradox table, I need some code for Delphi 2.0 that does the trick.

The existing columns was made with fielddefs

with Table1.FieldDefs do
begin
  Clear;
  Add('Column1', ftString, 50, False);
  Add('Column2', ftString, 50, False);
end;
Table1.CreateTable;

if I try to add another column after table1.createtable was used,
I get an error.

Table1.FieldDefs.Add('Field3', ftString, 25, False);
Table1.FieldDefs.Update;
DBEdit3.DataField := 'Field3';  <-- error 'Field3 dosn't exist!'

If I call Table1.CreateTable again the whole table will be erased, all the information written in the table are lost.

Would someone give me an example that matches my table?
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Expert Comment

by:ronit051397
ID: 1347746
What's wrong with SQL?
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Expert Comment

by:Marcius
ID: 1347747
The use of fielddefs will not create a row in the underlying table. It is an operator designed to manipulate TDataset, not the underlying table.

I really think that the best solution is to use SQL. Other than that, you can re-create a new table each time you want to add a column, migrate the data, then destroy the old table. As you can see, SQL is the cleaner option.
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Author Comment

by:koger
ID: 1347748
Ok, how do I use SQL?
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Expert Comment

by:ronit051397
ID: 1347749
I have already posted the answer on SQL and you rejected it.
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Author Comment

by:koger
ID: 1347750
To Ronit.

The reason that I really didn't want(ed) to use SQL, is that my application don't use SQL and I haven't used SQL before.

you gave me this SQL statement,

  SQL.Text:='ALTER TABLE "ANIMALS.dbf" ADD TEST SMALLINT';

I need a string field with the length 25, I haven't got any manual that covers SQL statements, so it is a bit tricky to figure out how the statement should look, will help me with that?
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Accepted Solution

by:
ronit051397 earned 100 total points
ID: 1347751
This must be done exclusively, meaning the table cannot be active in your application or another application, while SQL is executing:

with Query1 do
begin
    DatabaseName:='DBDEMOS';
    SQL.Text:='ALTER TABLE "ANIMALS.dbf" ADD TEST CHAR(25)';
    ExecSQL;
 end;

for more information on SQL statements see:
C:\Program Files\Borland\Common Files\BDE\Localsql.hlp
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Author Comment

by:koger
ID: 1347752
Thanx!!
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