add index to ExpiresAt (#426)

src/DotNetCore.CAP.MySql/IStorage.MySql.cs

@@ -70,7 +70,8 @@ CREATE TABLE IF NOT EXISTS `{prefix}.received` (
   `Added` datetime NOT NULL,
   `ExpiresAt` datetime DEFAULT NULL,
   `StatusName` varchar(50) NOT NULL,
-  PRIMARY KEY (`Id`)
+  PRIMARY KEY (`Id`),
+  INDEX `IX_ExpiresAt`(`ExpiresAt`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
 
 CREATE TABLE IF NOT EXISTS `{prefix}.published` (
@@ -82,7 +83,8 @@ CREATE TABLE IF NOT EXISTS `{prefix}.published` (
   `Added` datetime NOT NULL,
   `ExpiresAt` datetime DEFAULT NULL,
   `StatusName` varchar(40) NOT NULL,
-  PRIMARY KEY (`Id`)
+  PRIMARY KEY (`Id`),
+  INDEX `IX_ExpiresAt`(`ExpiresAt`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
 ";
             return batchSql;