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Add basic JSON_TABLE() functionality

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JSON_TABLE() allows JSON data to be converted into a relational view
and thus used, for example, in a FROM clause, like other tabular
data.  Data to show in the view is selected from a source JSON object
using a JSON path expression to get a sequence of JSON objects that's
called a "row pattern", which becomes the source to compute the
SQL/JSON values that populate the view's output columns.  Column
values themselves are computed using JSON path expressions applied to
each of the JSON objects comprising the "row pattern", for which the
SQL/JSON query functions added in 6185c9737c are used.

To implement JSON_TABLE() as a table function, this augments the
TableFunc and TableFuncScanState nodes that are currently used to
support XMLTABLE() with some JSON_TABLE()-specific fields.

Note that the JSON_TABLE() spec includes NESTED COLUMNS and PLAN
clauses, which are required to provide more flexibility to extract
data out of nested JSON objects, but they are not implemented here
to keep this commit of manageable size.

Author: Nikita Glukhov <n.gluhov@postgrespro.ru>
Author: Teodor Sigaev <teodor@sigaev.ru>
Author: Oleg Bartunov <obartunov@gmail.com>
Author: Alexander Korotkov <aekorotkov@gmail.com>
Author: Andrew Dunstan <andrew@dunslane.net>
Author: Amit Langote <amitlangote09@gmail.com>
Author: Jian He <jian.universality@gmail.com>

Reviewers have included (in no particular order):

Andres Freund, Alexander Korotkov, Pavel Stehule, Andrew Alsup,
Erik Rijkers, Zihong Yu, Himanshu Upadhyaya, Daniel Gustafsson,
Justin Pryzby, Álvaro Herrera, Jian He

Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
Discussion: https://postgr.es/m/20220616233130.rparivafipt6doj3@alap3.anarazel.de
Discussion: https://postgr.es/m/abd9b83b-aa66-f230-3d6d-734817f0995d%40postgresql.org
Discussion: https://postgr.es/m/CA+HiwqE4XTdfb1nW=Ojoy_tQSRhYt-q_kb6i5d4xcKyrLC1Nbg@mail.gmail.com
This commit is contained in:
Amit Langote
2024-04-04 19:57:08 +09:00
parent a9d6c38684
commit de3600452b
35 changed files with 2943 additions and 52 deletions
Download Patch File Download Diff File Expand all files Collapse all files

53
src/backend/parser/parse_expr.c
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@ -4245,7 +4245,8 @@ transformJsonSerializeExpr(ParseState *pstate, JsonSerializeExpr *expr)
}
/*
* Transform JSON_VALUE, JSON_QUERY, JSON_EXISTS functions into a JsonExpr node.
* Transform JSON_VALUE, JSON_QUERY, JSON_EXISTS, JSON_TABLE functions into
* a JsonExpr node.
*/
static Node *
transformJsonFuncExpr(ParseState *pstate, JsonFuncExpr *func)
@ -4269,6 +4270,9 @@ transformJsonFuncExpr(ParseState *pstate, JsonFuncExpr *func)
func_name = "JSON_VALUE";
default_format = JS_FORMAT_DEFAULT;
break;
case JSON_TABLE_OP:
func_name = "JSON_TABLE";
break;
default:
elog(ERROR, "invalid JsonFuncExpr op %d", (int) func->op);
break;
@ -4350,6 +4354,42 @@ transformJsonFuncExpr(ParseState *pstate, JsonFuncExpr *func)
jsexpr->returning->typmod = -1;
}
/* JSON_TABLE() COLUMNS can specify a non-boolean type. */
if (jsexpr->returning->typid != BOOLOID)
{
Node *coercion_expr;
CaseTestExpr *placeholder = makeNode(CaseTestExpr);
int location = exprLocation((Node *) jsexpr);
/*
* We abuse CaseTestExpr here as placeholder to pass the
* result of evaluating JSON_EXISTS to the coercion
* expression.
*/
placeholder->typeId = BOOLOID;
placeholder->typeMod = -1;
placeholder->collation = InvalidOid;
coercion_expr =
coerce_to_target_type(pstate, (Node *) placeholder, BOOLOID,
jsexpr->returning->typid,
jsexpr->returning->typmod,
COERCION_EXPLICIT,
COERCE_IMPLICIT_CAST,
location);
if (coercion_expr == NULL)
ereport(ERROR,
(errcode(ERRCODE_CANNOT_COERCE),
errmsg("cannot cast type %s to %s",
format_type_be(BOOLOID),
format_type_be(jsexpr->returning->typid)),
parser_coercion_errposition(pstate, location, (Node *) jsexpr)));
if (coercion_expr != (Node *) placeholder)
jsexpr->coercion_expr = coercion_expr;
}
jsexpr->on_error = transformJsonBehavior(pstate, func->on_error,
JSON_BEHAVIOR_FALSE,
jsexpr->returning);
@ -4414,6 +4454,17 @@ transformJsonFuncExpr(ParseState *pstate, JsonFuncExpr *func)
jsexpr->returning);
break;
case JSON_TABLE_OP:
if (!OidIsValid(jsexpr->returning->typid))
{
jsexpr->returning->typid = exprType(jsexpr->formatted_expr);
jsexpr->returning->typmod = -1;
}
jsexpr->on_error = transformJsonBehavior(pstate, func->on_error,
JSON_BEHAVIOR_EMPTY,
jsexpr->returning);
break;
default:
elog(ERROR, "invalid JsonFuncExpr op %d", (int) func->op);
break;