学习理解语法的语法

i want to use alter table

我想使用alter table

but the syntax posted here:

但是这里发布的语法:

http://dev.mysql.com/doc/refman/5.1/en/alter-table.html

is very confusing

非常混乱

i do not understand what the [ ] mean or the { } mean or the pipes

我不明白[]是什么意思或{}意思或管道

is there some kind of tutorial that can help me understand this?

是否有某种教程可以帮助我理解这一点?

4 个解决方案

#1

The brackets [ ] denote optional expressions

方括号[]表示可选表达式

The pipes mean OR.

管道意味着OR。

The braces { } group words for the pipes.

大括号{}组合管道的单词。

For example:

[COLUMN] means that the word COLUMN can optionally appear

[COLUMN]表示可以选择显示单词COLUMN

{INDEX|KEY} means that either INDEX or KEY must appear

{INDEX | KEY}表示必须出现INDEX或KEY

[FIRST | AFTER col_name ] means that the word FIRST or AFTER (the name of a column) can optionally appear

[FIRST | AFTER col_name]表示可以选择显示单词FIRST或AFTER(列名)

#2

[] means, that argument inside is optional
{a|b} means that you have to choose whether a or b

[]表示,里面的参数是可选的{a | b}意味着你必须选择a或b

UPD: specifically for mysql you should look over here: http://dev.mysql.com/doc/refman/5.1/en/manual-conventions.html

UPD:专门针对mysql你应该看看这里:http://dev.mysql.com/doc/refman/5.1/en/manual-conventions.html

#3

Example of an alter table statement to add a column to a table:

用于向表中添加列的alter table语句的示例:

ALTER TABLE tablename ADD COLUMN columnname INT

changing a column's name:

更改列名称:

ALTER TABLE tablename CHANGE COLUMN columnname newname INT

rename table:

ALTER TABLE tablename RENAME newname

drop a field from a table

从表中删除一个字段

ALTER TABLE tablename DROP columname

On the syntax side, the user @SLaks has a good answer.

在语法方面,用户@SLaks有一个很好的答案。

#4

Oh well. It's the full reference and I think for starting it's really an overkill. Maybe you should try more simple and informal guides on the topic, like http://www.w3schools.com/sql/sql_alter.asp or http://infogoal.com/sql/sql-alter-table.htm etc. etc. If you get a book covering basic SQL stuff I'm quite sure that you'll find a nice explanation, too. If you understand the basics, you can go with the more complicated stuff in the reference (if you need it).

好吧。这是完整的参考,我认为开始它真的是一种矫枉过正。也许您应该尝试更多关于该主题的简单和非正式指南,如http://www.w3schools.com/sql/sql_alter.asp或http://infogoal.com/sql/sql-alter-table.htm等。如果你得到一本涵盖基本SQL内容的书,我很确定你也能找到一个很好的解释。如果您了解基础知识,则可以使用参考中更复杂的内容(如果需要)。

#1

The brackets [ ] denote optional expressions