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Showing posts with the label PRIMARY KEY

Table Indexing

When a row is inserted into a table, the database server does not attempt to put the data in any particular  location within the table.  Instead, the server simply places the data in the next available location within the  file.  When a query is sent against the table therefore, the server will need to inspect every row of the table  to answer the query.  Tables in MySQL can grow very large, and as a table gets bigger, retrievals from it  become slower.  An index in MySQL serves to assist in finding row data more quickly and easily, much like an index in the  back of a technical manual.  Database indexes are used to locate rows in a table.  Indexes are special  structures that, unlike normal tables, are kept in a specific order.  Instead of containing all of the data about  an entity, however, an index contains only the column(s) used to locate rows in the data table.  It also  contains information describing where the rows are physically located.  Usually, all the indexes requi