docs: Add CLAUDE.md with codebase guidance

Create comprehensive documentation for future Claude Code instances working in this repository, including:
- Development commands for testing, building, and code quality
- Core architecture overview of the SQL query builder system
- Directory structure and component explanations
- Testing patterns and conventions
- Key dependencies and their purposes

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

schema/dialect/mysql/mysql.go

@@ -3,11 +3,11 @@ package mysql
 import (
 	"strings"
 
-	"git.fsdpf.net/go/db/v2"
-	"git.fsdpf.net/go/db/v2/dialect/mysql"
-	"git.fsdpf.net/go/db/v2/internal/sb"
-	"git.fsdpf.net/go/db/v2/schema"
-	"git.fsdpf.net/go/db/v2/sqlgen"
+	"git.fsdpf.net/go/db"
+	"git.fsdpf.net/go/db/dialect/mysql"
+	"git.fsdpf.net/go/db/internal/sb"
+	"git.fsdpf.net/go/db/schema"
+	"git.fsdpf.net/go/db/sqlgen"
 )
 
 type Mysql struct {
@@ -16,6 +16,7 @@ type Mysql struct {
 }
 
 var mysqlDefaultModifiers = []string{
+
 	"Unsigned", "Charset", "Collate", "VirtualAs", "StoredAs",
 	"Nullable", "Default", "Increment", "Comment", "After", "First",
 }
@@ -47,29 +48,33 @@ func (this Mysql) TableExists(table string) (bool, error) {
 // 创建表
 func (this Mysql) CompileCreate(bp *schema.Blueprint) []string {
 	temporary := db.L("CREATE")
-	if bp.IsTemporary() {
+	if bp.Temporary {
 		temporary = db.L("CREATE TEMPORARY")
 	}
 	columns := strings.Join(this.getAddedColumns(bp), ",\n")
 
 	sql := this.GenerateSQL("? TABLE ? (\n?\n)", temporary, db.T(bp.GetTable()), db.L(columns))
 
-	charset := bp.GetCharset()
+	charset := bp.Charset
 	if charset == "" {
 		charset = "utf8mb4"
 	}
 
-	collation := bp.GetCollation()
+	collation := bp.Collation
 	if collation == "" {
 		collation = "utf8mb4_general_ci"
 	}
 
 	sql += this.GenerateSQL(" default charset=? collate=?", charset, collation)
 
-	if engine := bp.GetEngine(); engine != "" {
+	if engine := bp.Engine; engine != "" {
 		sql += this.GenerateSQL(" engine=?", engine)
 	}
 
+	if comment := bp.Comment; comment != "" {
+		sql += this.GenerateSQL(" comment=?", comment)
+	}
+
 	return []string{sql}
 }
 
@@ -121,13 +126,18 @@ func (this Mysql) CompileRename(bp *schema.Blueprint) []string {
 	if len(commands) == 0 {
 		panic("new table undefined")
 	}
-	toName = bp.GetCommands()[0].To
+	toName = commands[0].To
 	if toName == "" {
 		panic("new table undefined")
 	}
 	return []string{this.GenerateSQL("RENAME TABLE ? TO ?", db.T(bp.GetTable()), db.T(toName))}
 }
 
+// 修改表备注
+func (this Mysql) CompileModifyComment(bp *schema.Blueprint) []string {
+	return []string{this.GenerateSQL("ALTER TABLE ? COMMENT = ?", db.T(bp.GetTable()), db.V(bp.Comment))}
+}
+
 func (this Mysql) addModifiers(sql string, bp *schema.Blueprint, column *schema.ColumnDefinition) string {
 	for _, modifier := range mysqlDefaultModifiers {
 		sql += this.GetColumnModifier(modifier, bp, column)