*: support show collation radondb#677

[summary]
support show collation
[test case]
src/vendor/github.com/xelabs/go-mysqlstack/sqlparser/show_test.go
src/proxy/show_test.go
[patch codecov]
src/proxy/show.go 88.2%

src/proxy/query.go

@@ -200,6 +200,12 @@ func (spanner *Spanner) ComQuery(session *driver.Session, query string, bindVari
 				log.Error("proxy.JDBC.shows[%s].from.session[%v].error:%+v", query, session.ID(), err)
 				status = 1
 			}
+		case sqlparser.ShowCollationStr:
+			// Support for DBeaver.
+			if qr, err = spanner.handleShowCollation(session, query, node); err != nil {
+				log.Error("proxy.show.collation.status[%s].from.session[%v].error:%+v", query, session.ID(), err)
+				status = 1
+			}
 		default:
 			log.Error("proxy.show.unsupported[%s].from.session[%v]", query, session.ID())
 			status = sqldb.ER_UNKNOWN_ERROR

src/proxy/show.go

@@ -623,3 +623,7 @@ func (spanner *Spanner) handleShowVersions(session *driver.Session, query string
 func (spanner *Spanner) handleJDBCShows(session *driver.Session, query string, node sqlparser.Statement) (*sqltypes.Result, error) {
 	return spanner.ExecuteSingle(query)
 }
+
+func (spanner *Spanner) handleShowCollation(session *driver.Session, query string, node sqlparser.Statement) (*sqltypes.Result, error) {
+	return spanner.ExecuteSingle(query)
+}

src/proxy/show_test.go

@@ -1198,13 +1198,13 @@ func TestProxyShowVersions(t *testing.T) {
 	}
 }
 
-func TestProxyShowWarnings(t *testing.T) {
+func TestProxyShowSupported(t *testing.T) {
 	log := xlog.NewStdLog(xlog.Level(xlog.PANIC))
 	fakedbs, proxy, cleanup := MockProxy(log)
 	defer cleanup()
 	address := proxy.Address()
 
-	querys := []string{"show warnings", "show variables"}
+	querys := []string{"show warnings", "show variables", "show collation"}
 	// fakedbs.
 	{
 		fakedbs.AddQueryPattern("use .*", &sqltypes.Result{})