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Unique keys play an important part in all relational databases, as they tie everything together. A unique key is a column that identifies a given entity, whereas a foreign key is a column in another table that refers to a primary key. Keys can comprise several columns, in which case they are composite keys.
A minimal edit script that transforms the former into the latter is: kitten → sitten (substitute "s" for "k") sitten → sittin (substitute "i" for "e") sittin → sitting (insert "g" at the end) LCS distance (insertions and deletions only) gives a different distance and minimal edit script: kitten → itten (delete "k" at 0)
Typical streams include log files, delimiter-separated values, or email messages, notably for email filtering. For example, an AWK program may take as input a stream of log statements, and for example send all to the console, write ones starting with WARNING to a "WARNING" file, and send an email to a sysadmin in case any line starts with ...
In IF commands and other syntax that has expressions evaluated as conditions, any string value is evaluated as a numeric value and, if that is a nonzero value, then it is interpreted as True. a<b yields 1 if a is less than b, 0 otherwise. Declarations None. All variables are dynamically created at the first time a value is assigned. Lines
Additional indexes (unique or non-unique) may be defined; these are called "secondary indexes". Views have the same purpose as in the underlying database: they define subsets of columns (and/or rows) from one or – using a join condition – several tables. Since views are virtual tables (they refer to data in other tables) they do not take a ...
All the candidate keys of a relation can uniquely identify the records of the relation, but only one of them is used as the primary key of the relation. The remaining candidate keys are called unique keys because they can uniquely identify a record in a relation. Unique keys can consist of multiple columns. Unique keys are also called alternate ...
In many applications, the range of hash values may be different for each run of the program or may change along the same run (for instance, when a hash table needs to be expanded). In those situations, one needs a hash function which takes two parameters—the input data z , and the number n of allowed hash values.
A parsing expression is a kind of pattern that each string may either match or not match.In case of a match, there is a unique prefix of the string (which may be the whole string, the empty string, or something in between) which has been consumed by the parsing expression; this prefix is what one would usually think of as having matched the expression.