sql, jobs: stop queuing schema change jobs for in-txn schema changes

Creating a table and changing its schema within a transaction would
cause a schema change job to be queued. Such jobs are not necessary and
don't do anything. This patch prevents them from being queued in the
first place.

Fixes #45985.

Release note (sql change): Creating a table and changing its schema
within a transaction no longer schedules a schema change job.

pkg/sql/logictest/testdata/logic_test/alter_table

@@ -1495,3 +1495,16 @@ CREATE TABLE t54629 (c INT NOT NULL, UNIQUE INDEX (c));
 ALTER TABLE t54629 ADD CONSTRAINT pk PRIMARY KEY (c);
 INSERT INTO t54629 VALUES (1);
 DELETE FROM t54629 WHERE c = 1;
+
+subtest regression_45985
+
+statement ok
+BEGIN;
+CREATE TABLE t45985 (a INT);
+ALTER TABLE t45985 ADD COLUMN b INT;
+COMMIT;
+
+query I
+SELECT count(*) FROM [SHOW JOBS] WHERE job_type = 'SCHEMA CHANGE' AND description LIKE 'ALTER TABLE test.public.t45985 %'
+----
+0

pkg/sql/table.go

@@ -223,8 +223,10 @@ func (p *planner) writeSchemaChange(
 		return errors.Errorf("no schema changes allowed on table %q as it is being dropped",
 			tableDesc.Name)
 	}
-	if err := p.createOrUpdateSchemaChangeJob(ctx, tableDesc, jobDesc, mutationID); err != nil {
-		return err
+	if !tableDesc.IsNew() {
+		if err := p.createOrUpdateSchemaChangeJob(ctx, tableDesc, jobDesc, mutationID); err != nil {
+			return err
+		}
 	}
 	return p.writeTableDesc(ctx, tableDesc)
 }