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PostgreSQL-Rezepte: Abrufen von Spaltentypen in einer Abfrage

Um das Abrufen von Spaltentypen in einer Anfrage vorzubereiten, benötigen wir Postgres . Sie können auch das fertige Bild verwenden .

Ich beeile mich sofort zu enttäuschen: Die Implementierung wird nicht in SQL sein! Obwohl, über und es gibt geeignete Funktionen. Aber der resultierende Code schien mir zu kompliziert und hässlich, und deshalb habe ich alles auf ... C implementiert! Das stimmt leider nicht als Erweiterung, sondern als Modifikation der Quelle.

Hier tatsächlich der Patch selbst zum Hinzufügen von Spaltentypen zu Namen (für Client-Versionen 2 und 3) mit Kommentaren

diff --git a/src/backend/access/common/printtup.c b/src/backend/access/common/printtup.c
index 24d6cd0249..6862b69258 100644
--- a/src/backend/access/common/printtup.c
+++ b/src/backend/access/common/printtup.c
@@ -22,6 +22,9 @@
 #include "utils/lsyscache.h"
 #include "utils/memdebug.h"
 #include "utils/memutils.h"
+#include "utils/guc.h"        // 
+#include "utils/syscache.h"   // 
+#include "catalog/pg_type.h"  // 
 
 
 static void printtup_startup(DestReceiver *self, int operation,
@@ -70,6 +73,8 @@ typedef struct
 	MemoryContext tmpcontext;	/* Memory context for per-row workspace */
 } DR_printtup;
 
+static bool append; //     ?
+
 /* ----------------
  *		Initialize: create a DestReceiver for printtup
  * ----------------
@@ -132,6 +137,7 @@ printtup_startup(DestReceiver *self, int operation, TupleDesc typeinfo)
 {
 	DR_printtup *myState = (DR_printtup *) self;
 	Portal		portal = myState->portal;
+	append = GetConfigOption("config.append_type_to_column_name", true, true) != NULL; //         ?
 
 	/*
 	 * Create I/O buffer to be used for all messages.  This cannot be inside
@@ -236,6 +242,7 @@ SendRowDescriptionCols_3(StringInfo buf, TupleDesc typeinfo, List *targetlist, i
 	 * character set overhead.
 	 */
 	enlargeStringInfo(buf, (NAMEDATALEN * MAX_CONVERSION_GROWTH /* attname */
+							+ (append ? NAMEDATALEN * MAX_CONVERSION_GROWTH + sizeof("::") - 1 : 0) //       ,       
 							+ sizeof(Oid)	/* resorigtbl */
 							+ sizeof(AttrNumber)	/* resorigcol */
 							+ sizeof(Oid)	/* atttypid */
@@ -283,6 +290,17 @@ SendRowDescriptionCols_3(StringInfo buf, TupleDesc typeinfo, List *targetlist, i
 		else
 			format = 0;
 
+		if (append) { //       , 
+			HeapTuple typeTuple = SearchSysCache1(TYPEOID, ObjectIdGetDatum(att->atttypid)); //     
+			StringInfoData buf_; //    
+			initStringInfo(&buf_); //  
+			appendStringInfo(&buf_, "%s::", NameStr(att->attname)); //      ,   
+			if (HeapTupleIsValid(typeTuple)) appendStringInfoString(&buf_, NameStr(((Form_pg_type) GETSTRUCT(typeTuple))->typname)); //    ,     
+			else appendStringInfo(&buf_, "%i", att->atttypid); //     oid
+			pq_writestring(buf, buf_.data); //   
+			ReleaseSysCache(typeTuple); //  
+			pfree(buf_.data); //   
+		} else //          ,    -
 		pq_writestring(buf, NameStr(att->attname));
 		pq_writeint32(buf, resorigtbl);
 		pq_writeint16(buf, resorigcol);
@@ -311,6 +329,17 @@ SendRowDescriptionCols_2(StringInfo buf, TupleDesc typeinfo, List *targetlist, i
 		/* If column is a domain, send the base type and typmod instead */
 		atttypid = getBaseTypeAndTypmod(atttypid, &atttypmod);
 
+		if (append) { //       , 
+			HeapTuple typeTuple = SearchSysCache1(TYPEOID, ObjectIdGetDatum(att->atttypid)); //     
+			StringInfoData buf_; //    
+			initStringInfo(&buf_); //  
+			appendStringInfo(&buf_, "%s::", NameStr(att->attname)); //      ,   
+			if (HeapTupleIsValid(typeTuple)) appendStringInfoString(&buf_, NameStr(((Form_pg_type) GETSTRUCT(typeTuple))->typname)); //    ,     
+			else appendStringInfo(&buf_, "%i", att->atttypid); //     oid
+			pq_sendstring(buf, buf_.data); //   
+			ReleaseSysCache(typeTuple); //  
+			pfree(buf_.data); //   
+		} else //          ,    -
 		pq_sendstring(buf, NameStr(att->attname));
 		/* column ID only info appears in protocol 3.0 and up */
 		pq_sendint32(buf, atttypid);
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 6c2db93573..f23de7f788 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -992,6 +992,8 @@ exec_simple_query(const char *query_string)
 	bool		use_implicit_block;
 	char		msec_str[32];
 
+	SetConfigOption("config.append_type_to_column_name", NULL, PGC_USERSET, PGC_S_SESSION); //    SQL-   ,     ,     
+
 	/*
 	 * Report query to various monitoring facilities.
 	 */
@@ -1959,6 +1961,8 @@ exec_execute_message(const char *portal_name, long max_rows)
 	bool		was_logged = false;
 	char		msec_str[32];
 
+	SetConfigOption("config.append_type_to_column_name", NULL, PGC_USERSET, PGC_S_SESSION); //      SQL-   ,     ,     
+
 	/* Adjust destination to tell printtup.c what to do */
 	dest = whereToSendOutput;
 	if (dest == DestRemote)

Nun, und ein Bonus, ein ähnlicher Patch zum Hinzufügen von Spaltentypen zu Namen bei der Konvertierung in json

diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index 26d293709a..fb025adf58 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -32,6 +32,7 @@
 #include "utils/jsonapi.h"
 #include "utils/typcache.h"
 #include "utils/syscache.h"
+#include "utils/guc.h" //   
 
 /*
  * The context of the parser is maintained by the recursive descent
@@ -106,6 +107,8 @@ static void add_json(Datum val, bool is_null, StringInfo result,
 					 Oid val_type, bool key_scalar);
 static text *catenate_stringinfo_string(StringInfo buffer, const char *addon);
 
+static bool append; //     ?
+
 /* the null action object used for pure validation */
 static JsonSemAction nullSemAction =
 {
@@ -1789,6 +1792,17 @@ composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 		needsep = true;
 
 		attname = NameStr(att->attname);
+		if (append) { //       , 
+			HeapTuple typeTuple = SearchSysCache1(TYPEOID, ObjectIdGetDatum(att->atttypid)); //     
+			StringInfoData buf; //    
+			initStringInfo(&buf); //  
+			appendStringInfo(&buf, "%s::", attname); //      ,   
+			if (HeapTupleIsValid(typeTuple)) appendStringInfoString(&buf, NameStr(((Form_pg_type) GETSTRUCT(typeTuple))->typname)); //    ,     
+			else appendStringInfo(&buf, "%i", att->atttypid); //     oid
+			escape_json(result, buf.data); //  
+			ReleaseSysCache(typeTuple); //  
+			pfree(buf.data); //   
+		} else //          ,    -
 		escape_json(result, attname);
 		appendStringInfoChar(result, ':');
 
@@ -1848,6 +1862,7 @@ array_to_json(PG_FUNCTION_ARGS)
 {
 	Datum		array = PG_GETARG_DATUM(0);
 	StringInfo	result;
+	append = GetConfigOption("config.append_type_to_column_name", true, true) != NULL; //         ?
 
 	result = makeStringInfo();
 
@@ -1865,6 +1880,7 @@ array_to_json_pretty(PG_FUNCTION_ARGS)
 	Datum		array = PG_GETARG_DATUM(0);
 	bool		use_line_feeds = PG_GETARG_BOOL(1);
 	StringInfo	result;
+	append = GetConfigOption("config.append_type_to_column_name", true, true) != NULL; //         ?
 
 	result = makeStringInfo();
 
@@ -1881,6 +1897,7 @@ row_to_json(PG_FUNCTION_ARGS)
 {
 	Datum		array = PG_GETARG_DATUM(0);
 	StringInfo	result;
+	append = GetConfigOption("config.append_type_to_column_name", true, true) != NULL; //         ?
 
 	result = makeStringInfo();
 
@@ -1898,6 +1915,7 @@ row_to_json_pretty(PG_FUNCTION_ARGS)
 	Datum		array = PG_GETARG_DATUM(0);
 	bool		use_line_feeds = PG_GETARG_BOOL(1);
 	StringInfo	result;
+	append = GetConfigOption("config.append_type_to_column_name", true, true) != NULL; //         ?
 
 	result = makeStringInfo();
 
@@ -1917,6 +1935,7 @@ to_json(PG_FUNCTION_ARGS)
 	StringInfo	result;
 	JsonTypeCategory tcategory;
 	Oid			outfuncoid;
+	append = GetConfigOption("config.append_type_to_column_name", true, true) != NULL; //         ?
 
 	if (val_type == InvalidOid)
 		ereport(ERROR,
@@ -1945,6 +1964,7 @@ json_agg_transfn(PG_FUNCTION_ARGS)
 				oldcontext;
 	JsonAggState *state;
 	Datum		val;
+	append = GetConfigOption("config.append_type_to_column_name", true, true) != NULL; //         ?
 
 	if (!AggCheckCallContext(fcinfo, &aggcontext))
 	{
@@ -2046,6 +2066,7 @@ json_object_agg_transfn(PG_FUNCTION_ARGS)
 				oldcontext;
 	JsonAggState *state;
 	Datum		arg;
+	append = GetConfigOption("config.append_type_to_column_name", true, true) != NULL; //         ?
 
 	if (!AggCheckCallContext(fcinfo, &aggcontext))
 	{

Nun, warum habe ich das alles gemacht ?! Weil ich zwar nicht nur eine interessante Idee habe, wie es effektiv eingesetzt werden kann, sondern meine Hände bisher noch nicht erreicht haben ...

Beispiel
set config.append_type_to_column_name = true;
with s as (
    select * from task
) select json_agg(s) from s
[{"id::int8":1,"parent::int8":null,"dt::timestamptz":"2020-05-20T07:53:03.952542+05:00","start::timestamptz":"2020-05-20T07:53:04.930703+05:00","stop::timestamptz":"2020-05-20T07:53:04.976998+05:00","group::text":"group","max::int4":null,"pid::int4":5905,"request::text":"select now()","response::text":"2020-05-20 07:53:04.976151+05","state::state":"DONE","timeout::interval":null,"delete::bool":false,"repeat::interval":null,"drift::bool":true,"count::int4":null,"live::interval":null,"remote::text":null,"append::bool":false,"header::bool":true,"string::bool":true,"null::text":"\\N","delimiter::char":"\t","quote::char":null,"escape::char":null},  {"id::int8":2,"parent::int8":null,"dt::timestamptz":"2020-05-20T07:53:12.780313+05:00","start::timestamptz":"2020-05-20T07:53:13.299168+05:00","stop::timestamptz":"2020-05-20T07:53:13.352304+05:00","group::text":"group","max::int4":null,"pid::int4":5908,"request::text":"select 1","response::text":"1","state::state":"DONE","timeout::interval":null,"delete::bool":false,"repeat::interval":null,"drift::bool":true,"count::int4":null,"live::interval":null,"remote::text":null,"append::bool":false,"header::bool":true,"string::bool":true,"null::text":"\\N","delimiter::char":"\t","quote::char":null,"escape::char":null},  {"id::int8":3,"parent::int8":null,"dt::timestamptz":"2020-05-20T07:53:15.954607+05:00","start::timestamptz":"2020-05-20T07:53:16.477578+05:00","stop::timestamptz":"2020-05-20T07:53:16.536582+05:00","group::text":"group","max::int4":null,"pid::int4":5910,"request::text":"select 1/0","response::text":"elevel\t20\noutput_to_server\ttrue\nfilename\tint.c\nlineno\t822\nfuncname\tint4div\ndomain\tpostgres-12\ncontext_domain\tpostgres-12\nsqlerrcode\t33816706\nmessage\tdivision by zero\nmessage_id\tdivision by zero\nROLLBACK","state::state":"FAIL","timeout::interval":null,"delete::bool":false,"repeat::interval":null,"drift::bool":true,"count::int4":null,"live::interval":null,"remote::text":null,"append::bool":false,"header::bool":true,"string::bool":true,"null::text":"\\N","delimiter::char":"\t","quote::char":null,"escape::char":null}]

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