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Mysql Unique Index

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Using MySQL UNIQUE Index To Prevent Duplicates

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Luckily, MySQL provides another kind of index called UNIQUE index that allows you to enforce the uniqueness of values in one or more columns. Unlike the ...

MySQL 8.0 Reference Manual :: 13.1.15 CREATE INDEX Statement

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A UNIQUE index creates a constraint such that all values in the index must be distinct. An error occurs if you try to add a new row with a key value that matches an ...

MySQL Unique Index - javatpoint

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MySQL UNIQUE INDEX ... Indexing is a process to find an unordered list into an ordered list that allows us to retrieve records faster. It creates an entry for each ...

MySQL 5.7 Reference Manual :: 13.1.14 CREATE INDEX Statement

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A UNIQUE index creates a constraint such that all values in the index must be distinct. An error occurs if you try to add a new row with a key value that matches an ...

SQL UNIQUE Constraint

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The UNIQUE constraint ensures that all values in a column are different. ... MySQL: ALTER TABLE Persons DROP INDEX UC_Person;. SQL Server / Oracle / MS ...

How to Use Unique Indexes in MySQL and Other Databases ...

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Dec 9, 2013 ... Unique indexes work in much the same way as a primary key. Although you can only have one primary key, any number of unique indexes can ...

Differences between INDEX, PRIMARY, UNIQUE, FULLTEXT in ...

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Apr 2, 2009 ... Differences · KEY or INDEX refers to a normal non-unique index. · UNIQUE refers to an index where all rows of the index must be unique.

MySQL UNIQUE INDEX | Learn How UNIQUE INDEX works in ...

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UNIQUE INDEX constraints are used in MySQL to maintain the uniqueness of values in the database. MySQL has the 'PRIMARY KEY' constraint to define unique ...

MySQL: unique field needs to be an index? - Stack Overflow

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Feb 22, 2012 ... No, you dont have to index it again. When you specify UNIQUE KEY , the column is indexed. So it has no difference in performance with other ...

MySQL Bugs: #8173: unique index allows duplicates with null values

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Jan 28, 2005 ... Description: unique index allows duplicates if at least one of the columns is null. How to repeat: mysql> create table tb -> ( -> id int not null ...

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