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transactions in sqlbegin transaction commit and rollback sql has the same syntax except for start in place of begin however start transaction is used
effects of null for multiple assignments - sqlif the row expression given as the source for a multiple assignment evaluates to null then null is
multiple assignment- sqlsql supports multiple assignment to local variables and also applies multiple assignment semantics in set clauses of update
merge and truncate in sqlsql has two more table update operators merge and truncate merge like insert takes a source table s and uses it to update a
example of delete - sqlas with update a for portion of clause can be specified if the target table has a defined period name as illustrated in
delete command - sqlloosely speaking delete removes some existing rows from its target table suppose the university decides that course c3 is to be
update command- sqlloosely speaking update changes some of the column values of some existing rows of its target table thus although some rows
example of except operator - sqlexample like its counterpart in the theory book illustrates the convenience of allowing any table expression to be
insert command in sqlloosely speaking insert takes the rows of a given source table and adds them to the specified target table retaining all the
updating tables in sqlthe topic of updating by describing the assignment operator in tutorial d sql uses a different syntax for assignment using the
example of foreign key constraintexample alternative formulation for 63 as a foreign key constraintalter table exammarkadd constraint
example of when or then constraintsa concrete example showing how sql supports whenthen constraintscreate table salhistory empno char 6salary integer
when or then key constraintssuppose a table has two columns representing a period of time throughout which the information conveyed by the other
effects of null for unique specificationwhen a unique specification u for base table t includes a column c that is not subject to a not null
keys in sqlsql support for keys in the following respectssql does not require at least one key for every base table if no key is explicitly declared
primary key - sqla primary key specification carries an implicit not null constraint on each column of the specified key when more than one key
example of shorthand for a row constraintexample shorthand for a row constraintalter table exammarkadd constraint markinrangecheck mark between 0 and
check constraints in sqla check constraint is a table constraint defined using the key word check as already illustrated in several examples in this
effects of null in aggregate operator - sqllet aggopx be an invocation of some aggregate operator aggop in sql where x is an expression usually an
effects of null for table expressionheres an important distinction between expressions denoting tables and expressions denoting multisets of rows a
between and not between operator in sqlexample restricting exam marks to between 0 and 100create assertion marksbetween0and100check not exists select
use of table comparisons - sqltable comparisons where it is noted that although table expressions cannot be compared we have table t to convert a
example of not exists operator - sqlexample is a translation into sql of the corresponding example which is included there merely to show that for
example of alternative formulation as a table constraintexample alternative formulation as a table constraintalter table exammarkadd constraint
example of not exists in sqlexample use of not existscreate assertion mustbeenrolledtotakeexamalternative1check not exists select studentid