sql: implement pg_is_other_temp_schema

Needed for cockroachdb#69010.

This commit implements the `pg_is_other_temp_schema` builtin function.
`pg_is_other_temp_schema` returns true if the given OID is the OID of another
session's temporary schema. This can be useful, for example, to exclude other
sessions' temporary tables from a catalog display.

Release note (sql change): The pg_is_other_temp_schema builtin function is now
supported, which returns whether the given OID is the OID of another session's
temporary schema.

Release justification: None, waiting for v22.1.

docs/generated/sql/functions.md

@@ -3138,6 +3138,8 @@ SELECT * FROM crdb_internal.check_consistency(true, ‘\x02’, ‘\x04’)</p>
 </span></td></tr>
 <tr><td><a name="pg_get_serial_sequence"></a><code>pg_get_serial_sequence(table_name: <a href="string.html">string</a>, column_name: <a href="string.html">string</a>) &rarr; <a href="string.html">string</a></code></td><td><span class="funcdesc"><p>Returns the name of the sequence used by the given column_name in the table table_name.</p>
 </span></td></tr>
+<tr><td><a name="pg_is_other_temp_schema"></a><code>pg_is_other_temp_schema(oid: oid) &rarr; <a href="bool.html">bool</a></code></td><td><span class="funcdesc"><p>Returns true if the given OID is the OID of another session’s temporary schema. (This can be useful, for example, to exclude other sessions’ temporary tables from a catalog display.)</p>
+</span></td></tr>
 <tr><td><a name="pg_my_temp_schema"></a><code>pg_my_temp_schema() &rarr; oid</code></td><td><span class="funcdesc"><p>Returns the OID of the current session’s temporary schema, or zero if it has none (because it has not created any temporary tables).</p>
 </span></td></tr>
 <tr><td><a name="pg_relation_is_updatable"></a><code>pg_relation_is_updatable(reloid: oid, include_triggers: <a href="bool.html">bool</a>) &rarr; int4</code></td><td><span class="funcdesc"><p>Returns the update events the relation supports.</p>

pkg/bench/rttanalysis/orm_queries_bench_test.go

@@ -197,6 +197,22 @@ WHERE
               CREATE TEMP TABLE t(a int primary key, b int)`,
 			Stmt: `SELECT pg_my_temp_schema() FROM generate_series(1, 10)`,
 		},
+
+		{
+			Name: "pg_is_other_temp_schema",
+			Setup: `SET experimental_enable_temp_tables = true;
+              CREATE TEMP TABLE t(a int primary key, b int)`,
+			Stmt: `SELECT nspname, pg_is_other_temp_schema(oid) FROM
+               (SELECT * FROM pg_namespace WHERE nspname = 'public') n`,
+		},
+
+		{
+			Name: "pg_is_other_temp_schema multiple times",
+			Setup: `SET experimental_enable_temp_tables = true;
+              CREATE TEMP TABLE t(a int primary key, b int)`,
+			Stmt: `SELECT nspname, pg_is_other_temp_schema(oid) FROM
+               (SELECT * FROM pg_namespace LIMIT 5) n`,
+		},
 	}
 
 	RunRoundTripBenchmark(b, tests)

pkg/sql/logictest/testdata/logic_test/pg_builtins

@@ -379,6 +379,42 @@ true
 statement ok
 SET DATABASE = test;
 
+# pg_is_other_temp_schema
+#
+# Returns true if the provided OID meets the following conditions:
+# - is a reference to a schema
+# - that is temporary
+# - and is owned by a different session
+
+query B
+SELECT pg_is_other_temp_schema((SELECT oid FROM pg_type LIMIT 1))
+----
+false
+
+query B
+SELECT pg_is_other_temp_schema((SELECT oid FROM pg_namespace WHERE nspname = 'pg_catalog'))
+----
+false
+
+query TB
+SELECT user, pg_is_other_temp_schema((SELECT oid FROM pg_namespace WHERE nspname LIKE 'pg_temp_%'))
+----
+root  false
+
+# Switch users as a means of switching sessions. GRANT to ensure visibility.
+
+statement ok
+GRANT root TO testuser
+
+user testuser
+
+query TB
+SELECT user, pg_is_other_temp_schema((SELECT oid FROM pg_namespace WHERE nspname LIKE 'pg_temp_%'))
+----
+testuser  true
+
+user root
+
 # information_schema._pg_truetypid and information_schema._pg_truetypmod
 #
 # We can't exhaustively test these until we support domain types.

pkg/sql/sem/builtins/pg_builtins.go

@@ -863,6 +863,40 @@ var pgBuiltins = map[string]builtinDefinition{
 		},
 	),
 
+	// pg_is_other_temp_schema returns true if the given OID is the OID of another
+	// session's temporary schema.
+	// https://www.postgresql.org/docs/11/functions-info.html
+	"pg_is_other_temp_schema": makeBuiltin(defProps(),
+		tree.Overload{
+			Types:      tree.ArgTypes{{"oid", types.Oid}},
+			ReturnType: tree.FixedReturnType(types.Bool),
+			Fn: func(ctx *tree.EvalContext, args tree.Datums) (tree.Datum, error) {
+				schemaArg := tree.UnwrapDatum(ctx, args[0])
+				schema, err := getNameForArg(ctx, schemaArg, "pg_namespace", "nspname")
+				if err != nil {
+					return nil, err
+				}
+				if schema == "" {
+					// OID does not exist.
+					return tree.DBoolFalse, nil
+				}
+				if !strings.HasPrefix(schema, catconstants.PgTempSchemaName) {
+					// OID is not a reference to a temporary schema.
+					//
+					// This string matching is what Postgres does too. See isAnyTempNamespace.
+					return tree.DBoolFalse, nil
+				}
+				if schema == ctx.SessionData().SearchPath.GetTemporarySchemaName() {
+					// OID is a reference to this session's temporary schema.
+					return tree.DBoolFalse, nil
+				}
+				return tree.DBoolTrue, nil
+			},
+			Info:       "Returns true if the given OID is the OID of another session's temporary schema. (This can be useful, for example, to exclude other sessions' temporary tables from a catalog display.)",
+			Volatility: tree.VolatilityStable,
+		},
+	),
+
 	// TODO(bram): Make sure the reported type is correct for tuples. See #25523.
 	"pg_typeof": makeBuiltin(tree.FunctionProperties{NullableArgs: true},
 		tree.Overload{