code: func (p *preprocessor) checkContainDotColumn(stmt *ast.CreateTableStmt) {
  	tName := stmt.Table.Name.String()
  	sName := stmt.Table.Schema.String()
  
  	for _, colDef := range stmt.Cols {
  		// check schema and table names.
  		if colDef.Name.Schema.O != sName && len(colDef.Name.Schema.O) != 0 {
  			p.err = ddl.ErrWrongDBName.GenWithStackByArgs(colDef.Name.Schema.O)
  			return
  		}
  		if colDef.Name.Table.O != tName && len(colDef.Name.Table.O) != 0 {
  			p.err = ddl.ErrWrongTableName.GenWithStackByArgs(colDef.Name.Table.O)
  			return
  		}
  	}
  }
docs: // checkContainDotColumn checks field contains the table name.
  // for example :create table t (c1.c2 int default null).