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Support XMLTABLE query expression

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XMLTABLE is defined by the SQL/XML standard as a feature that allows
turning XML-formatted data into relational form, so that it can be used
as a <table primary> in the FROM clause of a query.

This new construct provides significant simplicity and performance
benefit for XML data processing; what in a client-side custom
implementation was reported to take 20 minutes can be executed in 400ms
using XMLTABLE.  (The same functionality was said to take 10 seconds
using nested PostgreSQL XPath function calls, and 5 seconds using
XMLReader under PL/Python).

The implemented syntax deviates slightly from what the standard
requires.  First, the standard indicates that the PASSING clause is
optional and that multiple XML input documents may be given to it; we
make it mandatory and accept a single document only.  Second, we don't
currently support a default namespace to be specified.

This implementation relies on a new executor node based on a hardcoded
method table.  (Because the grammar is fixed, there is no extensibility
in the current approach; further constructs can be implemented on top of
this such as JSON_TABLE, but they require changes to core code.)

Author: Pavel Stehule, Álvaro Herrera
Extensively reviewed by: Craig Ringer
Discussion: https://postgr.es/m/CAFj8pRAgfzMD-LoSmnMGybD0WsEznLHWap8DO79+-GTRAPR4qA@mail.gmail.com
This commit is contained in:
Alvaro Herrera
2017-03-08 12:39:37 -03:00
parent 270d7dd8a5
commit fcec6caafa
52 changed files with 4606 additions and 50 deletions
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33
src/backend/parser/parse_coerce.c
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@ -1096,9 +1096,9 @@ coerce_to_boolean(ParseState *pstate, Node *node,
}
/*
* coerce_to_specific_type()
* Coerce an argument of a construct that requires a specific data type.
* Also check that input is not a set.
* coerce_to_specific_type_typmod()
* Coerce an argument of a construct that requires a specific data type,
* with a specific typmod. Also check that input is not a set.
*
* Returns the possibly-transformed node tree.
*
@ -1106,9 +1106,9 @@ coerce_to_boolean(ParseState *pstate, Node *node,
* processing is wanted.
*/
Node *
coerce_to_specific_type(ParseState *pstate, Node *node,
Oid targetTypeId,
const char *constructName)
coerce_to_specific_type_typmod(ParseState *pstate, Node *node,
Oid targetTypeId, int32 targetTypmod,
const char *constructName)
{
Oid inputTypeId = exprType(node);
@ -1117,7 +1117,7 @@ coerce_to_specific_type(ParseState *pstate, Node *node,
Node *newnode;
newnode = coerce_to_target_type(pstate, node, inputTypeId,
targetTypeId, -1,
targetTypeId, targetTypmod,
COERCION_ASSIGNMENT,
COERCE_IMPLICIT_CAST,
-1);
@ -1144,6 +1144,25 @@ coerce_to_specific_type(ParseState *pstate, Node *node,
return node;
}
/*
* coerce_to_specific_type()
* Coerce an argument of a construct that requires a specific data type.
* Also check that input is not a set.
*
* Returns the possibly-transformed node tree.
*
* As with coerce_type, pstate may be NULL if no special unknown-Param
* processing is wanted.
*/
Node *
coerce_to_specific_type(ParseState *pstate, Node *node,
Oid targetTypeId,
const char *constructName)
{
return coerce_to_specific_type_typmod(pstate, node,
targetTypeId, -1,
constructName);
}
/*
* parser_coercion_errposition - report coercion error location, if possible