DBExpress: How to find a primary key field?

Question

I have a TSimpleDataSet based on dinamically created SQL query. I need to know which field is a primary key?

SimpleDataSet1.DataSet.SetSchemaInfo(stIndexes, 'myTable' ,'');

This code tells me that i have a primary key with name 'someName', but how can i know which field (column) works with this index?

Answer 1

A Primary Key/Index can belong to several columns (not just one).

The schema stIndexes dataset will return the PK name INDEX_NAME and the columns that construct that PK/Index (COLUMN_NAME). INDEX_TYPE will tell you which index types you have (eSQLNonUnique/eSQLUnique/eSQLPrimaryKey).

I have never worked with TSimpleDataSet but check if the indexes information is stored in IndexDefs[TIndexDef].Name/Fields/Options - if ixPrimary in Options then this is your PK. and Fields belongs to that index.

Take a look at the source at SqlExpr.pas: TCustomSQLDataSet.AddIndexDefs. Note how TCustomSQLDataSet returns the TableName (and then the indexs information) from the command text:

  ...
  if FCommandType = ctTable then
    TableName := FCommandText
  else
    TableName := GetTableNameFromSQL(CommandText);
  DataSet := FSQLConnection.OpenSchemaTable(stIndexes, TableName, '', '', '');
  ...

Answer 2

I think the simple data set does not provide that information.

However, i am sure there are components for that. Check, for Oracle database, Devart's ODAC. Basically, it involves only one query to the database. However, it is not something that components will offer by default as, because it involves a different query, it leads to slow response times.

For Oracle database, query on user_indexes.