查询表列数的SQL语句：

SELECT COUNT(*) FROM USER_TAB_COLUMNS WHERE TABLE_NAME=UPPER('legalentity')

MYSQL中的外键：

/==============================================================/
/* DBMS name: MySQL 4.0 /
/ Created on: 2005-8-9 16:38:37 /
/==============================================================*/

drop table if exists Article;

drop table if exists Board;

drop table if exists User;

/==============================================================/
/* Table: Article /
/==============================================================*/
create table Article
(
id int not null primary key,
parent_id int,
index(parent_id),
foreign key (parent_id) references Article (id) ,
board_id int not null,
index(board_id),
foreign key (board_id) references Board (id) ,
article_type int not null,
title varchar(255) not null,
body text,
create_by int not null,
index(create_by),
foreign key (create_by) references User (id) ,
create_time datetime not null,
hits int not null,
bytes int,
last_update_by int not null,
index(last_update_by),
foreign key (last_update_by) references User (id),
last_update_time datetime not null,
)
type = InnoDB;

/==============================================================/
/* Table: Board /
/==============================================================*/
create table Board
(
id int not null primary key,
create_by int not null,
index(create_by),
foreign key (create_by) references User (id),
parent_id int,
index(parent_id),
foreign key (parent_id) references Board (id),
name varchar(50) not null,
remark varchar(255),
create_time datetime not null,
)
type = InnoDB;

/==============================================================/
/* Table: User /
/==============================================================*/
create table User
(
id int not null primary key,
name varchar(50) not null,
pwd varchar(50) not null,
)
type = InnoDB;