用sql查看表结构

1.oracle
 sql   = "SELECT column_name, data_type, data_length, nullable";
 sql += " from user_tab_columns ";
 sql += " where table_name='";
 sql += $tableName;
 sql += "'";
 select * from user_tab_comments   查询表名及表说明（comment)
 select * from user_col_comments    查询表及表中字段的说明
2.sql server
select  name,xtype,length,isnullable  from  syscolumns
where id =(select  top 1 Id   from  sysobjects  where name = '表名');
 
 sql   = "select  name,xtype,length,isnullable  from  syscolumns where id =";
 sql += " (select  top 1 Id   from  sysobjects  where name = '";
 sql += $tableName;
 sql += "')";
3.my sql
 sql   = "show columns from ";
 sql += $tableName;
或
 sql   = "desc ";
 sql += $tableName;
或
 sql   = "describe ";
 sql += $tableName;