try to fix Rows.Scan with NULL able column

advisor/index.go

@@ -785,7 +785,6 @@ func CompleteColumnsInfo(stmt sqlparser.Statement, cols []*common.Column, env *e
 				if find {
 					break
 				}
-
 			}
 
 			// 如果不依赖env环境，利用ast中包含的信息推理列的库表信息
@@ -904,7 +903,7 @@ func (idxAdv *IndexAdvisor) calcCardinality(cols []*common.Column) []*common.Col
 				// 如果是不存在的表就会报错，报错的可能性有三个：
 				// 1.数据库错误  2.表不存在  3.临时表
 				// 而这三种错误都是不需要在这一层关注的，直接跳过
-				common.Log.Debug("calcCardinality error: %v", err)
+				common.Log.Warn("calcCardinality error: %v", err)
 				continue
 			}
 

database/show.go

@@ -18,10 +18,11 @@ package database
 
 import (
 	"fmt"
-	"github.com/XiaoMi/soar/common"
 	"regexp"
 	"strconv"
 	"strings"
+
+	"github.com/XiaoMi/soar/common"
 )
 
 // SHOW TABLE STATUS Syntax
@@ -191,6 +192,10 @@ func NewTableIndexInfo(tableName string) *TableIndexInfo {
 func (db *Connector) ShowIndex(tableName string) (*TableIndexInfo, error) {
 	tbIndex := NewTableIndexInfo(tableName)
 
+	if db.Database == "" || tableName == "" {
+		return nil, fmt.Errorf("database('%s') or table('%s') name should not empty", db.Database, tableName)
+	}
+
 	// 执行 show create table
 	res, err := db.Query(fmt.Sprintf("show index from `%s`.`%s`", db.Database, tableName))
 	if err != nil {
@@ -456,12 +461,14 @@ func (db *Connector) FindColumn(name, dbName string, tables ...string) ([]*commo
 
 	var col common.Column
 	for res.Rows.Next() {
+		var character, collation string
 		res.Rows.Scan(&col.Table,
 			&col.DB,
 			&col.DataType,
-			&col.Character,
-			&col.Collation)
-
+			&character,
+			&collation)
+		col.Character = character
+		col.Collation = collation
 		// 填充字符集和排序规则
 		if col.Character == "" {
 			// 当从`INFORMATION_SCHEMA`.`COLUMNS`表中查询不到相关列的character和collation的信息时
@@ -479,13 +486,13 @@ func (db *Connector) FindColumn(name, dbName string, tables ...string) ([]*commo
 				return columns, err
 			}
 
-			var tbCollation string
+			var tbCollation []byte
 			if newRes.Rows.Next() {
 				newRes.Rows.Scan(&tbCollation)
 			}
-			if tbCollation != "" {
-				col.Character = strings.Split(tbCollation, "_")[0]
-				col.Collation = tbCollation
+			if string(tbCollation) != "" {
+				col.Character = strings.Split(string(tbCollation), "_")[0]
+				col.Collation = string(tbCollation)
 			}
 		}
 		columns = append(columns, &col)