src: fix column name with no quote when scatter to backends radondb#489

[summary]
When scatter sql to backends, the column name should be with quote '`'
e.g.: create table db.t(`key` int primary key, `col` int);
For the ddl with rename table, we remove all quotes '`' to uniform
standars.
e.g.: alter table t1 rename t2.

[test case]
src/planner/ddl_plan_test.go

[patch codecov]
src/planner/ddl_plan.go 95.1%
coverage: 89.8% of statements

src/planner/ddl_plan.go

@@ -132,26 +132,23 @@ func (p *DDLPlan) Build() error {
 			var query string
 
 			orgSegTable := segment.Table
-			var rawQuery string
 			var re *regexp.Regexp
 			var segTable string
 			if node.Table.Qualifier.IsEmpty() {
 				segTable = fmt.Sprintf("`%s`.`%s`", database, orgSegTable)
-				rawQuery = strings.Replace(p.RawQuery, "`", "", -1)
 				// \b: https://www.regular-expressions.info/wordboundaries.html
 				re, _ = regexp.Compile(fmt.Sprintf(`\b(%s)\b`, table))
 			} else {
 				segTable = fmt.Sprintf("`%s`.`%s`", database, orgSegTable)
 				newTable := fmt.Sprintf("%s.%s", database, table)
-				rawQuery = strings.Replace(p.RawQuery, "`", "", -1)
 				re, _ = regexp.Compile(fmt.Sprintf(`\b(%s)\b`, newTable))
 			}
 
 			// avoid the name of the column is the same as the table name, eg, issues/438
 			// just replace the first place.
 			var count = 0
 			var occurrence = 1
-			query = re.ReplaceAllStringFunc(rawQuery, func(m string) string {
+			query = re.ReplaceAllStringFunc(p.RawQuery, func(m string) string {
 				count = count + 1
 				if count == occurrence {
 					return segTable
@@ -163,6 +160,8 @@ func (p *DDLPlan) Build() error {
 				var segQuery string
 				var segToTable string
 				var re *regexp.Regexp
+				// Here we default make sql with no quote '`'.
+				query = strings.Replace(query, "`", "", -1)
 				pos := strings.Index(query, segTable)
 				pos += len(segTable)
 
@@ -185,12 +184,14 @@ func (p *DDLPlan) Build() error {
 				}
 
 				if node.NewName.Qualifier.IsEmpty() {
-					segToTable = fmt.Sprintf("`%s`.`%s`", database, segToTable)
+					// Here we default make sql with no quote '`'.
+					segToTable = fmt.Sprintf("%s.%s", database, segToTable)
 					segQuery = strings.Replace(query[pos:], "`", "", -1)
 					// \b: https://www.regular-expressions.info/wordboundaries.html
 					re, _ = regexp.Compile(fmt.Sprintf(`\b(%s)\b`, toTable))
 				} else {
-					segToTable = fmt.Sprintf("`%s`.`%s`", database, segToTable)
+					// Here we default make sql with no quote '`'.
+					segToTable = fmt.Sprintf("%s.%s", database, segToTable)
 					newToTable := fmt.Sprintf("%s.%s", database, toTable)
 					segQuery = strings.Replace(query[pos:], "`", "", -1)
 					re, _ = regexp.Compile(fmt.Sprintf(`\b(%s)\b`, newToTable))
@@ -241,6 +242,8 @@ func (p *DDLPlan) JSON() string {
 		RawQuery:   p.RawQuery,
 		Partitions: parts,
 	}
+	// If exp include escape, json will add '\' before it.
+	// e.g.: "\n\t tbl \n" will be "\\n\\t tbl \\n"
 	bout, err := json.MarshalIndent(exp, "", "\t")
 	if err != nil {
 		return err.Error()