The following tables list examples of expressions for tutd, Project:M36's "Tutorial D" implementation.
Relational expressions query database state without being able to change it.
| Relational Expression | Description |
|---|---|
:showexpr p |
Display the relation variable p |
:showexpr s rename {city as town} |
Display the result after renaming a relational attribute |
:showexpr p{color,city} |
Display the result of the projection on the color and city attributes |
:showexpr p{all but city} |
Display the result of the projection of all attribute of p except city |
:showexpr p join sp |
Display the result of the relational expression p joined against sp (equivalent to NATURAL JOIN in SQL) |
:showexpr (s join sp){all from s} |
Display the result of a join but only include attributes from s |
:showexpr s semijoin sp |
Equivalent to (s join sp){all from s} |
:showexpr s antijoin sp |
Display the result of all tuples in s which do not match appear in the result of s semijoin sp |
:showexpr s union s |
Display the result of s unioned with itself (which is equivalent to s) |
:showexpr s:{status2:=add(10,@status)} |
Display the result of extending the s relation variable with a new attribute which adds 10 to each status attribute |
:showexpr (s:{islondon:=if eq(@city,"London") then True else False}){city,islondon} |
Display the result of relation variable s extended with a new attribute islondon which is the result of a conditional. |
:showexpr s where lt(@status, 30) |
Display the result of s where the status is less than 30. |
:showexpr s relwhere (p{}) |
Display the result of s if the p relation variable is non-empty. |
:showexpr s group ({sname,status,s#} as subrel) |
Display the result of grouping the sname, status, and s# into a subrel for each tuple in the s relation where the city attribute (not mentioned) is the grouping criteria |
| `:showexpr s group ({all but city} as g):{city_total:=sum(@g.status)} | Display the result of grouping suppliers by city and the sum total status of each city. |
:showexpr (s group ({sname,status,s#} as subrel)) ungroup subrel |
Display the result of unwrapping a subrelation to create one new tuple for each subrelation tuple in the result |
:showexpr s minus s |
Display the result after removing all tuples that match the second argument. x minus x is equivalent to x where false |
:showexpr relation{tuple{name "Mike",age 6},tuple{name "Sam",age 10}} |
Display an unnamed relation using manually constructed tuples |
:showexpr relation{a Integer, b Text} |
Display an empty-tupled relation of a specified type |
:showexpr relation{a Integer, b Text}{tuple{a 4, b "four"}} |
Display a relation bound by the specified types and containing one or more tuples |
:showexpr s group ({s#,sname,status} as subrel):{citycount:=count(@subrel)} |
Display a result which groups s by city and extends the relation by a count for each city. |
:showrelvars |
Display a list of relation variables in the current context along with their types (attributes) |
| Example Value Expression | Type | Explanation |
|---|---|---|
"abc" |
Text | UTF-8 string |
123 |
Integer | an integer of limitless size (using gmp) |
int(456) |
Int | machine-word-based integer |
12.56 |
Double | 64-bit IEEE 754 floating point number |
dateTimeFromEpochSeconds(1502304846) |
DateTime | |
fromGregorian(2017,05,30) |
Date | |
True |
Bool | True or False (not to be conflated with true and false which are relation variables) |
bytestring("dGVzdGRhdGE=") |
Bytestring | base-64-encoded string of bytes |
interval(3,5,False,False) |
Interval(Integer) | the constructor function includes two bounds and two boolean flags for inclusiveness |
scientific(1,int(100)) |
Scientific | 1e100 |
Database context expressions take the current database context as input and alter it to create a new context.
| Database Context Expression | Description |
|---|---|
:importexample cjdate |
Imports a precooked schema from Chris Date's books resulting in relvars s, sp, and p |
:importtutd "file:///home/agentm/project-m36/scripts/emp.tutd" |
Imports TutorialD from file URI |
:importtutd "https://raw.githubusercontent.com/agentm/project-m36/master/scripts/emp.tutd" "effe32b247586dc3ac0079fc241b9618d41d189afcaeb7907edbe5a8b45992a4" |
Imports TutorialD from HTTP or HTTPS URI |
newrelvar:=relation{tuple{age 3}} |
Assign a new relation variable named newrelvar |
undefine s |
Remove a relation variable |
insert s relation{tuple{city "Boston",s# "S10",sname "Gonzalez",status 10}} |
Append to an existing relation variable with another relational expression |
update s where status=20 (sname:="Mr. Twenty") |
Replace one or more values in matching tuples with a new value |
delete sp where s#="S4" |
Remove tuples matching the criteria |
key s_key_constraint {s#} s |
Add a constraint named s_key_constraint on relation variable s ensuring that s# is unique |
foreign key s#_in_sp sp{s#} in s{s#} |
Add a foreign key constraint that ensures that sp's s# attribute always references a s# value in s |
constraint s_status_less_than_50 (s where gte(@status,50)){} in false |
Add a constraint that stipulates that the status values in s are less than 50 |
createarbitraryrelation employee {name Text, empid Int, hired DateTime} 3-100 |
Create a relation variable with random values with between 3-100 tuples- useful for testing |
notify steve_change person where name="Steve" true (person where name="Steve"){address} |
Notify the current connection with an asynchronous event if any committed tuples matching person where name="Steve" with true for the pre-change state and person where name="Steve"){address} for the post-change state- these states will be sent along with the notification |
| `data Hair = Bald | Brown |
undata Hair |
Delete the Hair custom type |
Relation variable and attribute names must begin with a lowercase letter unless quoted with backticks.
Transaction graph expressions alter the state of the transaction graph by append new states.
| Transaction Graph Expression | Description |
|---|---|
:commit |
Save the current database context to a new transaction and add it to the transaction graph |
:rollback |
Return the database context to the state before any alterations were made |
:branch experimental |
Create a new branch from the existing branch and switch the current context to be able to commit to the new branch |
:jumphead master |
Discard any changes in the current context and jump to the head of a different branch |
:jump 11b601c9-f46b-42b0-a2ce-cf18ced31b7f |
Jump to the specific transaction by UUID- useful for introspecting past states |
:showgraph |
Display a representation of the transaction graph |
:walkbacktotime "2017-08-10 16:44:00" |
Walk back in time from the current branch until a transaction less than or equal to the time is found and switch the current context to that past transaction- useful for auditing |
In contrast to relational expressions, data frame expressions generate ordered tuples.
| Data Frame Expression | Description |
|---|---|
:showdataframe s orderby {status} |
Display a data frame result for the relational expression s and sort the tuples by status |
:showdataframe s{status} orderby {status descending} offset 1 limit 3 |
Display a data frame result for s{status} but ordered by status values descending, skip the first tuple, and return no more than 3 tuples |
Trans-graph relational expressions allow queries spanning multiple transactions.
| Trans-Graph Relational Expressions | Description |
|---|---|
:showtransgraphexpr s@master join sp@master |
Display a result for joining s and sp on the branch master |
:showtransgraphexpr s@master~ join sp@master |
Display a result for joining s on the parent transaction of master's current head and sp on master |
:showtransgraphexpr s@master~^2 |
Display a result for s two parents previous to the parent of the current master's head |