如何使用sql在xml中定义PK？

Question

Is it possible to create the Primary key and Foreign key tag in xml using sql? like

  <Column Name="ID" DataType="INTEGER" IsPrimaryKey="true" />
  <ForeignKey SourceTable="Product" TargetTable="Market">
  <ColumnMap Source="ID" Target="ID" Ordinal="1" />
  </ForeignKey>

I use following part but it does not shows the PK and FK part:

    select COLUMN_NAME as '@Name',
           Data_type as '@DataType',
           character_octet_length as '@Length'
           FROM information_schema.COLUMNS 
    FOR XML PATH ('Column'), TYPE

Answer 1

An important thing to bear in mind is that primary and foreign keys are defined at table level, not against individual columns, which can lead to quite complex queries to build up the data you require. It is, for example, quite possible to have a primary key covering multiple fields; it's also quite common for a column to be defined as a foreign key on a large number of tables other than the one it belongs to.

With that in mind - and, due to time constraints - the following only handles primary keys, and I've only tested it on single-column primary keys:

  SELECT c.COLUMN_NAME as '@Name',
        c.TABLE_NAME as '@Table',
        Data_type as '@DataType',
        character_octet_length as '@Length', case when tc.CONSTRAINT_NAME IS NULL then 'false' else 'true' end as '@IsPrimaryKey'
    FROM information_schema.COLUMNS c
        left outer join INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcu on c.TABLE_NAME = kcu.TABLE_NAME and kcu.COLUMN_NAME = c.COLUMN_NAME
        left outer join  INFORMATION_SCHEMA.TABLE_CONSTRAINTS tc on tc.CONSTRAINT_NAME = kcu.CONSTRAINT_NAME and tc.CONSTRAINT_TYPE = 'PRIMARY KEY'
    FOR XML PATH ('Column'), TYPE

For clarity, I've included the table name in the output. Sample output:

<Column Name="AdministratorID" Table="Administrator" DataType="int"
    IsPrimaryKey="true" /><Column Name="UserName" Table="Administrator"
    DataType="varchar" Length="50" IsPrimaryKey="false" /><Column Name=
    ...

I realise this doesn't match your requirements exactly, but it should give you something to build upon.