builtins: fix error case of crdb_internal.hide_sql_constants

Fix one of the error cases of `hide_sql_constants` to append an empty
string to the array, rather than returning an empty string. Also, add
`hide_sql_constants` back to sqlsmith now that cockroachdb#96555 is fixed.

Epic: None

Fixes: cockroachdb#97830

Release note: None

pkg/internal/sqlsmith/schema.go

@@ -513,9 +513,6 @@ var functions = func() map[tree.FunctionClass]map[oid.Oid][]function {
 			"crdb_internal.revalidate_unique_constraint",
 			"crdb_internal.request_statement_bundle",
 			"crdb_internal.set_compaction_concurrency",
-			// TODO(96555): Temporarily disable crdb_internal.hide_sql_constants,
-			// which produces internal errors for some valid inputs.
-			"crdb_internal.hide_sql_constants",
 			// TODO(#97097): Temporarily disable crdb_internal.fingerprint
 			// which produces internal errors for some valid inputs.
 			"crdb_internal.fingerprint",

pkg/sql/logictest/testdata/logic_test/builtin_function

@@ -3736,6 +3736,11 @@ SELECT crdb_internal.hide_sql_constants(ARRAY('select 1', NULL, 'select ''hello'
 ----
 {"SELECT _",NULL,"SELECT '_'",""}
 
+query T
+SELECT crdb_internal.hide_sql_constants(ARRAY['banana'])
+----
+{""}
+
 query T
 SELECT crdb_internal.hide_sql_constants('SELECT ''yes'' IN (''no'', ''maybe'', ''yes'')')
 ----

pkg/sql/sem/builtins/builtins.go

@@ -7718,7 +7718,7 @@ expires until the statement bundle is collected`,
 				return tree.NewDString(sqlNoConstants), nil
 			},
 			types.String,
-			"Removes constants from a SQL statement. String provided must contain at most"+
+			"Removes constants from a SQL statement. String provided must contain at most "+
 				"1 statement.",
 			volatility.Immutable,
 		),
@@ -7742,11 +7742,11 @@ expires until the statement bundle is collected`,
 
 					if len(sql) != 0 {
 						parsed, err := parser.ParseOne(sql)
-						if err != nil {
-							return tree.NewDString(sqlNoConstants), nil //nolint:returnerrcheck
+						// If parsing is unsuccessful, we append an empty string instead of
+						// returning an error.
+						if err == nil {
+							sqlNoConstants = tree.AsStringWithFlags(parsed.AST, tree.FmtHideConstants)
 						}
-
-						sqlNoConstants = tree.AsStringWithFlags(parsed.AST, tree.FmtHideConstants)
 					}
 
 					if err := result.Append(tree.NewDString(sqlNoConstants)); err != nil {
@@ -7756,7 +7756,7 @@ expires until the statement bundle is collected`,
 
 				return result, nil
 			},
-			Info: "Hide constants for each element in an array of SQL statements." +
+			Info: "Hide constants for each element in an array of SQL statements. " +
 				"Note that maximum 1 statement is permitted per string element.",
 			Volatility: volatility.Immutable,
 		},