使用T-SQL将表转换为XML

Question

If found several questions about how to convert a table (or query) into XML, but none that showed how to start with one main table and join several one:many satellite tables, and from that generate XML that represents the hierarchical structure of the data. So I thought I'd share this solution now that I've figured it out. If someone else has another way of doing this, please post another answer.

Given this contrived data:

create table #recipe (id int, name varchar(10))
create table #ingredient (recipe_id int, name varchar(30), quantity varchar(20), sort int)
create table #instruction (recipe_id int, task varchar(32), sort int)

insert into #recipe values (1, 'pizza'), (2, 'omelet')
insert into #ingredient values (1, 'pizza dough', '1 package', 1),
                               (1, 'tomato sauce', '1 can', 2),
                               (1, 'favorite toppings', 'you choose', 3),
                               (2, 'eggs', 'three', 1),
                               (2, 'a bunch of other ingredients', 'you choose', 2)
insert into #instruction values (1, 'pre-bake pizza dough', 1),
                                (1, 'add tomato sauce', 2),
                                (1, 'add toppings', 3),
                                (1, 'bake a little longer', 4),
                                (2, 'break eggs into mixing bowl', 1),
                                (2, 'beat yolks and whites together', 2),
                                (2, 'pour into large sauce pan', 3),
                                (2, 'add other ingredients', 4),
                                (2, 'fold in half', 5),
                                (2, 'cook until done', 6)

.

Which looks like this in tabular form:

#recipe

id          name
----------- ----------
1           pizza
2           omelet

.

#ingredient

recipe_id   name                           quantity             sort
----------- ------------------------------ -------------------- -----------
1           pizza dough                    1 package            1
1           tomato sauce                   1 can                2
1           favorite toppings              you choose           3
2           eggs                           three                1
2           a bunch of other ingredients   you choose           2

.

#instruction

recipe_id   task                             sort
----------- -------------------------------- -----------
1           pre-bake pizza dough             1
1           add tomato sauce                 2
1           add toppings                     3
1           bake a little longer             4
2           break eggs into mixing bowl      1
2           beat yolks and whites together   2
2           pour into large sauce pan        3
2           add other ingredients            4
2           fold in half                     5
2           cook until done                  6

.

I want to create an XML document that has one record for each recipe, and within each recipe element, I want a group of ingredients and another group of instructions, like this:

<recipes>
  <recipe id="2" name="omelet">
    <ingredients>
      <ingredient name="eggs" quantity="three" />
      <ingredient name="a bunch of other ingredients" quantity="you choose" />
    </ingredients>
    <instructions>
      <instruction task="break eggs into mixing bowl" />
      <instruction task="beat yolks and whites together" />
      <instruction task="pour into large sauce pan" />
      <instruction task="add other ingredients" />
      <instruction task="fold in half" />
      <instruction task="cook until done" />
    </instructions>
  </recipe>
  <recipe id="1" name="pizza">
    <ingredients>
      <ingredient name="pizza dough" quantity="1 package" />
      <ingredient name="tomato sauce" quantity="1 can" />
      <ingredient name="favorite toppings" quantity="you choose" />
    </ingredients>
    <instructions>
      <instruction task="pre-bake pizza dough" />
      <instruction task="add tomato sauce" />
      <instruction task="add toppings" />
      <instruction task="bake a little longer" />
    </instructions>
  </recipe>
</recipes>

Answer 1

This SQL creates the desired XML verbatim:

select recipe.*,
       (
         select ingredient.name, ingredient.quantity
         from   #ingredient ingredient
         where recipe.id = ingredient.recipe_id
         order by ingredient.sort
         for xml auto, root('ingredients'), type
       ),
       (
         select instruction.task
         from   #instruction instruction
         where  recipe.id = instruction.recipe_id
         order by instruction.sort
         for xml auto, root('instructions'), type
       )
from   #recipe as recipe
order by recipe.name
for xml auto, root('recipes'), type

I aliased the temp table names because using for xml auto on temp tables creates poorly named XML elements. This is how it looks:

<recipes>
  <recipe id="2" name="omelet">
    <ingredients>
      <ingredient name="eggs" quantity="three" />
      <ingredient name="a bunch of other ingredients" quantity="you choose" />
    </ingredients>
    <instructions>
      <instruction task="break eggs into mixing bowl" />
      <instruction task="beat yolks and whites together" />
      <instruction task="pour into large sauce pan" />
      <instruction task="add other ingredients" />
      <instruction task="fold in half" />
      <instruction task="cook until done" />
    </instructions>
  </recipe>
  <recipe id="1" name="pizza">
    <ingredients>
      <ingredient name="pizza dough" quantity="1 package" />
      <ingredient name="tomato sauce" quantity="1 can" />
      <ingredient name="favorite toppings" quantity="you choose" />
    </ingredients>
    <instructions>
      <instruction task="pre-bake pizza dough" />
      <instruction task="add tomato sauce" />
      <instruction task="add toppings" />
      <instruction task="bake a little longer" />
    </instructions>
  </recipe>
</recipes>

.

This SQL creates another version of the XML with all data as values instead of attributes, but in the same basic hierarchical structure:

select recipe.*,
       (
         select ingredient.name, ingredient.quantity
         from   #ingredient ingredient
         where recipe.id = ingredient.recipe_id
         order by ingredient.sort
         for xml path('ingredient'), root('ingredients'), type
       ),
       (
         select instruction.task
         from   #instruction instruction
         where  recipe.id = instruction.recipe_id
         order by instruction.sort
         for xml path('instruction'), root('instructions'), type
       )
from   #recipe as recipe
order by recipe.name
for xml path('recipe'), root('recipes'), type

.

This is how it looks:

<recipes>
  <recipe>
    <id>2</id>
    <name>omelet</name>
    <ingredients>
      <ingredient>
        <name>eggs</name>
        <quantity>three</quantity>
      </ingredient>
      <ingredient>
        <name>a bunch of other ingredients</name>
        <quantity>you choose</quantity>
      </ingredient>
    </ingredients>
    <instructions>
      <instruction>
        <task>break eggs into mixing bowl</task>
      </instruction>
      <instruction>
        <task>beat yolks and whites together</task>
      </instruction>
      <instruction>
        <task>pour into large sauce pan</task>
      </instruction>
      <instruction>
        <task>add other ingredients</task>
      </instruction>
      <instruction>
        <task>fold in half</task>
      </instruction>
      <instruction>
        <task>cook until done</task>
      </instruction>
    </instructions>
  </recipe>
  <recipe>
    <id>1</id>
    <name>pizza</name>
    <ingredients>
      <ingredient>
        <name>pizza dough</name>
        <quantity>1 package</quantity>
      </ingredient>
      <ingredient>
        <name>tomato sauce</name>
        <quantity>1 can</quantity>
      </ingredient>
      <ingredient>
        <name>favorite toppings</name>
        <quantity>you choose</quantity>
      </ingredient>
    </ingredients>
    <instructions>
      <instruction>
        <task>pre-bake pizza dough</task>
      </instruction>
      <instruction>
        <task>add tomato sauce</task>
      </instruction>
      <instruction>
        <task>add toppings</task>
      </instruction>
      <instruction>
        <task>bake a little longer</task>
      </instruction>
    </instructions>
  </recipe>
</recipes>

Originally I tried placing the ingredients and instructions in the main query's from clause with an inner join to the recipe table. But the instructions were all nested within the ingredients, which were nested within the recipe. When I moved them up to the select part of the query it straightened out the XML.