{"id":971,"date":"2005-01-27T00:36:00","date_gmt":"2005-01-27T00:36:00","guid":{"rendered":"\/blogs\/bobb\/post\/Fun-with-static-XQuery-evaluation-2.aspx"},"modified":"2005-01-27T00:36:00","modified_gmt":"2005-01-27T00:36:00","slug":"fun-with-static-xquery-evaluation-2","status":"publish","type":"post","link":"https:\/\/www.sqlskills.com\/blogs\/bobb\/fun-with-static-xquery-evaluation-2\/","title":{"rendered":"Fun with static XQuery evaluation – 2"},"content":{"rendered":"

\nReference back to the previous entry. Now that we know the rules, let's try them out:\n<\/p>\n

\n— snip —\n<\/p>\n

\nData(),text() and string() accessors\n<\/p>\n

\nXQuery has a function fn:data() to extract scalar, typed values from nodes, a node test text() to return text nodes, and the function fn:string() that returns the string value of a node. Their usages are sometimes confusing. Guidelines for their proper use in SQL Server 2005 are as follows. Consider the XML instance <age>12<\/age>.\n<\/p>\n

\nUntyped XML: The path expression \/age\/text() returns the text node "12". The function fn:data(\/age) returns the string value "12" and so does fn:string(\/age).\n<\/p>\n

\nTyped XML: The expression \/age\/text() returns static error for any simple typed <age> element. On the other hand, fn:data(\/age) returns integer 12, while fn:string(\/age) yields the string "12".\n<\/p>\n

\n— snip —\n<\/p>\n

\nTry this:\n<\/p>\n

\nDECLARE @x xml
\nSET @x = '<age>12<\/age>'
\n— works as expected
\nSELECT @x.query('data(\/age)')
\nGO\n<\/p>\n

\nDECLARE @x xml
\nSET @x = '<age>12<\/age>'
\n— fails
\n— Msg 2211, Level 16, State 1, Line 6
\n— XQuery [query()]: Singleton (or empty sequence) required, found operand of type 'element(age,xdt:untypedAny) *'
\nSELECT @x.query('string(\/age)')
\nGO\n<\/p>\n

\nOh. This message looks familiar. It turns out that XQuery functions are strongly typed also. Here's the definition of fn:string and fn:data:\n<\/p>\n

\nfn:string($arg as item()?) as xs:string\n<\/p>\n

\nfn:data($arg as item()*) as xdt:anyAtomicType*\n<\/p>\n

\nThe "item()*" means that data takes a sequence of 0-n items. "item()?" means that string only takes a sequence of 0-1 item. Let's fix it then.\n<\/p>\n

\nSELECT @x.query('string(\/age[1])')\n<\/p>\n

\nCool. Here's the test for comprehension. Let's try this with typed XML.\n<\/p>\n

\n— start with a schema collection\n<\/p>\n

\nCREATE XML SCHEMA COLLECTION ages AS
\n'<xs:schema
\n   xmlns:xs="http:\/\/www.w3.org\/2001\/XMLSchema<\/a>"
\n   targetNamespace="urn:ages"
\n   xmlns:tns="urn:ages">
\n<xs:element name="age" type="xs:int"\/>
\n<\/xs:schema>
\n'
\nGO\n<\/p>\n

\nDECLARE @x xml(ages)
\nSET @x = '<age xmlns="urn:ages">12<\/age>'
\n— fails as expected
\nSELECT @x.query('
\ndeclare default namespace "urn:ages";
\n\/age\/text()')
\nGO\n<\/p>\n

\nDECLARE @x xml(ages)
\nSET @x = '<age xmlns="urn:ages">12<\/age>'
\n— works as expected
\nSELECT @x.query('
\ndeclare default namespace "urn:ages";
\ndata(\/age)')
\nGO\n<\/p>\n

\nDECLARE @x xml(ages)
\nSET @x = '<age>12<\/age>'
\n— fails ??!
\nSELECT @x.query('string(\/age)')
\nGO\n<\/p>\n

\nWhy does the last query (against strongly typed XML) fail, even though there is a schema? How can you fix it? There are two different "right answers".<\/p>\n","protected":false},"excerpt":{"rendered":"

Reference back to the previous entry. Now that we know the rules, let's try them out: — snip — Data(),text() and string() accessors XQuery has a function fn:data() to extract scalar, typed values from nodes, a node test text() to return text nodes, and the function fn:string() that returns the string value of a node. […]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[28,37],"tags":[],"class_list":["post-971","post","type-post","status-publish","format-standard","hentry","category-sql-server-2005","category-sql-server-xml"],"yoast_head":"\nFun with static XQuery evaluation - 2 - Bob Beauchemin<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.sqlskills.com\/blogs\/bobb\/fun-with-static-xquery-evaluation-2\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Fun with static XQuery evaluation - 2 - Bob Beauchemin\" \/>\n<meta property=\"og:description\" content=\"Reference back to the previous entry. Now that we know the rules, let's try them out: — snip — Data(),text() and string() accessors XQuery has a function fn:data() to extract scalar, typed values from nodes, a node test text() to return text nodes, and the function fn:string() that returns the string value of a node. 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Now that we know the rules, let's try them out: — snip — Data(),text() and string() accessors XQuery has a function fn:data() to extract scalar, typed values from nodes, a node test text() to return text nodes, and the function fn:string() that returns the string value of a node. 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