A table can have more than one MULTIPLE key. Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.It is also a set of one or more columns of a table which does not. This makes a much simpler SQL query: UPDATE Table1 SET l1 l1, l2 l2 FROM Table2 WHERE Table1.id Table2.id. It is quite like UNIQUE key to allow unique values but does not allow If you are using SQL Server you can update one table from another without specifying a join and simply link the two from the where clause.It is also a set of one or more columns of a table to uniquely identify the record.It is quite like primary key to allow unique values butĬan accept one null value which primary key does not.It is a set of one or more columns of a table to uniquely identify.Stick that in your neocortex and set the dial to "frappe". Mysql> create table skipper(id int, foreign key(id) references penguins(id)) | Field | Type | Null | Key | Default | Extra |Ī table with one column and an index on the one column has a MUL: mysql> create table penguins (foo INT, index(foo)) Ī table with a column that is a primary key has PRI mysql> create table penguins (foo INT primary key) Ī table with a column that is a unique key has UNI: mysql> create table penguins (foo INT unique) Ī table with an index covering foo and bar has MUL only on foo: mysql> create table penguins (foo INT, bar INT, index(foo, bar)) Ī table with two separate indexes on two columns has MUL for each one mysql> create table penguins (foo INT, bar int, index(foo), index(bar)) Ī table with an Index spanning three columns has MUL on the first: mysql> create table penguins (foo INT,Ī table with a foreign key that references another table's primary key is MUL mysql> create table penguins(id int primary key) 1 contributor Feedback In this article Debugging a stack overflow without symbols Analyzing a Single Function Call Debugging stack overflow when symbols are available Summary of commands See also A stack overflow is an error that user-mode threads can encounter.
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