Saving Data on Android

INTEGER
, 
VARCHAR
, 
FLOAT
 or 
DATETIME
 that help preserve the integrity of the information 
stored in your database.
Saving Data on Android
Chapter 6: Entity Definitions
raywenderlich.com
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For most of the tables, the first column will be used to store a 
primary key
 that 
uniquely identifies the record. Primary keys are values often represented as a series 
of integers that are incremented one by one (1,2,3,4,5,...). This is not always the case 
since you could also use any string that represents a unique value for each entry — 
like a randomly generated hash or a social security number if you have more complex 
security requirements. As such, the primary key is, at its core, the differentiating 
agent between records. You can quickly look up records by primary keys or compare 
two records to see if they are the same.
Primary keys also help you create relationships by defining a