Hello,
I have created some tables a while back, and of course, and I am
learning, I have found problems with duplicate entries and other
problems.
So upon a fresh read of the 5.1 docs, I am trying to understand the word
"symbol" after the constraint.
I would like to be able to somehow combine two columns, and make them
unique? Or distinct?. I do not want the same two columns to ever occur
again. If someone tries to insert, just ignore and continue. So I will
use a MyISAM table type. But in order to understand how this is done,
could use an understanding of the "symbol" behind constraint.
create_definition:
column_definition
| [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (index_col_name,...)
| KEY [index_name] [index_type] (index_col_name,...)
| INDEX [index_name] [index_type] (index_col_name,...)
| [CONSTRAINT [symbol]] UNIQUE [INDEX]
[index_name] [index_type] (index_col_name,...)
| FULLTEXT [INDEX] [index_name] (index_col_name,...)
[WITH PARSER parser_name]
| SPATIAL [INDEX] [index_name] (index_col_name,...)
| [CONSTRAINT [symbol]] FOREIGN KEY
[index_name] (index_col_name,...) [reference_definition]
| CHECK (expr)
