CS240A: Databases and Knowledge Bases TSQL2 Carlo Zaniolo Department of Computer Science University of California, Los Angeles Notes From Chapter 6 of Advanced Database Systems by Zaniolo, Ceri, Faloutsos, Snodgrass, Subrahmanian and Zicari. Morgan Kaufmann, 1997

TSQL2 Language Constructs  Schema Specification  Snapshot Queries  The FROM Clause---Restructuring  Valid­Time Selection  Valid­Time Projection  Modification Statements  Event Tables  Transaction Time  Aggregates  The NOW construct Many other constructs: Temporal Indeterminacy, Granularity,Schema Versioning, etc.

Schema Specification  Scenario: Patient records include information on the drugs prescribed to each patient.  The valid time specifies the period(s) during which the drug was prescribed.  The valid time has a granularity of day (transaction time granularity is system defined): CREATE TABLE Prescription (Name, Physician, Drug, Dosage, Frequency INTERVAL MINUTE) AS VALID DAY AND TRANSACTION

Six Different Kinds of Tables  Snapshot table: nothing after the attributes  Valid­time state table: AS VALID [ STATE ]  Valid­time event table: AS VALID EVENT  Transaction­time table: AS TRANSACTION  Bitemporal state table: AS VALID [ STATE ] AND TRANSACTION  Bitemporal event table: AS VALID EVENT AND TRANSACTION  The type of a table can be changed at any time, using the ALTER statement.

Snapshot Queries  Who has been prescribed drugs? SELECT SNAPSOT Name FROM Prescription  Result is a list of names of those with current or past prescriptions.  Who is or was taking the drug Proventi l ? SELECT SNAPSHOT Name FROM Prescription WHERE Drug = 'Proventil‘  Result is a list of names.

Valid Time History Queries  Can request history, rather than just current state.  Who has been prescribed drugs, and when? SELECT Name FROM Prescription  Result is a list of names, each associated with one or more maximal periods.  Since we have projection: coalescing is used to compute those maximal periods.

Temporal Joins  What drugs have been prescribed with Proventil? SELECT P1.Name, P2.Drug FROM Prescription AS P1, Prescription AS P2 WHERE P1.Drug = 'Proventil‘ AND P2.Drug <> `Proventil‘ AND P1.Name = P2.Name  Result is a list of patient names and drugs, along with their associated maximal period(s).

Temporal Projection  Who has been on a drug for more than a total of six months? SELECT Name, Drug FROM Prescription(Name, Drug) AS P WHERE CAST(VALID(P) AS INTERVAL MONTH) > INTERVAL '6' MONTH  Result will contain the maximal interval(s) when the patient has been on the drug---provided that the sum of all those intervals exceeds 6 months.

Restructuring  Nested SELECT projects on the specified attributes, then automatically coalesces the result. FROM R(B, C) AS MyR is equivalent to FROM (SELECT B, C FROM R) AS MyR Other attributes in R are not accessible via MyR, and A is not accessible in the enclosing SELECT.

Restructuring: coupling of correlation names  Who has been on Proventil throughout their drug regime? SELECT SNAPSHOT P1.Name FROM Prescription(Name) AS P1, P1(Drug) AS P2 WHERE P2.Drug = 'Proventil’ AND VALID(P2) = VALID(P1)  P1 contains all the times that any drug has been prescribed to a patient.  P2 is coalesced on the Name and Drug columns. Also, the values of the Name column for both P1 and P2 are identical.

Restructuring: very useful syntactic sugar SELECT... FROM A(B,C,D) AS A2, A2(E,F) AS A3 WHERE...  is equivalent to:SELECT... FROM (SELECT B,C,D FROM A) AS A2, (SELECT B,C,D,E,F FROM A) AS A3 WHERE... AND A2.B = A3.B AND A2.C=A3.C AND A2.D = A3.D AND VALID(A2) OVERLAPS VALID(A3)  Intuitively, A2 is timestamped with a temporal element when attributes B, C, and D remained constant, and A3 ranges over different values of D and E, with the timestamp of A3 being a subset of that of A2.

Partitioning  Who has been on the same drug for more than six consecutive months? SELECT Name, Drug FROM Prescription(Name, Drug) AS (Period) P WHERE CAST(VALID(P) AS INTERVAL MONTH) > INTERVAL '6' MONTH  P ranges over Name­Drug pairs associated with individual maximal periods.  The result may contain several rows with the same Name and Drug values.

Partitioning, cont.  Partitioning is more than syntactic sugar.  It violates the data model, in that it produces value­ equivalent tuples that the correlation name ranges over.  Note, however, that underlying tables and the result table are always coalesced so that the violation is temporary and internal to a query.  Useful for queries specifying “consecutive time” or “continuous periods”.

Valid­Time Projection  What drugs was Melanie prescribed during 1994? SELECT Drug VALID INTERSECT(VALID(Prescription), PERIOD '[1994]' DAY) FROM Prescription WHERE Name = 'Melanie‘  The result is a list of drugs, each associated with a set of the periods during 1994 that they were prescribed to Melanie.  A new clause, the VALID clause, specifies the timestamp of the resulting tuple.

Modification Statements  The valid times can be specified for rows that are being inserted.  Inserted values will be coalesced with existing value­ equivalent rows.  Default valid clause: INSERT INTO Prescription VALUES ('Sally','Dr. Beren','Proventil','100 mg', INTERVAL '8:00' MINUTE) VALID PERIOD '[1993/01/01 ­ 1993/06/30]‘ VALID PERIOD(CURRENT_TIMESTAMP, NOBIND(TIMESTAMP 'now'))  An INSERT statement with a subquery is handled in the same manner.

Modification Statements, cont.  The delete statement removes period(s) from the temporal element of the qualifying row(s).  The columns of a row can be changed, as in SQL­92. DELETE FROM Prescription WHERE Name = 'Melanie‘ VALID PERIOD '[1993­03­01 ­ 1993­05­31]‘ VALID PERIOD '[1994­03­01 ­ 1994­04­30]‘  If the temporal element becomes empty, the row itself is deleted (no valid time specified means ‘from now’) UPDATE Prescription SET Dosage TO '50 mg‘ WHERE Name = 'Melanie‘ AND Drug = 'Proventil'

Modification statements, cont.  The valid time of a row can also be changed: UPDATE Prescription SET Dosage TO '50 mg‘ VALID PERIOD '[1993­03­01 ­ 1993­07­30]'WHERE Name = 'Melanie‘ AND Drug = 'Proventil'

Modification Statements (Con’t) now Original DELETE yields UPDATE yields UPDATE with valid time yields

Event Tables  Event tables are timestamped with instant sets.  Each row identifies a particular kind of (instantaneous) event, with the timestamp of that row specifying the instant(s) when that event occurred.  Event tables may also be associated with transaction time: CREATE TABLE LabTest (Name, Physician, TestID) AS VALID EVENT HOUR AND TRANSACTION

Event Tables, cont.  Were any patients the sole receivers of tests ordered by a physician? SELECT L1.Name, L2.Physician FROM LabTest(Name) AS L1, L1(Physician) AS L2, LabTest(Physician) AS L3 WHERE VALID(L1) = VALID(L2) AND L2.Physician = L3.Physician AND VALID(L1) = VALID(L3)  VALID(L1) is an event set containing all tests done to a particular patient  VALID(L2) contains the times of all tests done to a particular patient and ordered by a particular physician  VALID(L3) is an event set containing all tests ordered by a particular physician.

Transaction Time  If transaction time is not mentioned in the query, the results include only the information currently believed to be true. E.g.: What is Melanie's prescription history? SELECT Drug FROM Prescription WHERE Name = 'Melanie'  Can also rollback the database. E.g.: What did the physician believe on June 1, 1994 was Melanie's prescription history? SELECT Drug FROM Prescription AS P WHERE Name = 'Melanie‘ AND TRANSACTION(P) OVERLAPS DATE '1994­06­01‘

Transaction Time, cont.  Auditing can be done on previously corrected data.  When was Melanie's data valid on January 1, 1993 last corrected? SELECT SNAPSHOT BEGIN(TRANSACTION(P2)) FROM Prescription AS P P2 WHERE P1.Name = 'Melanie' AND P1.Name = P2.Name AND VALID(P1) OVERLAPS DATE '1993­01­01‘ AND VALID(P2) OVERLAPS DATE '1993­01­01‘ AND TRANSACTION(P1) MEETS TRANSACTION(P2)

Transaction Time, cont.  The transaction timestamp is specified with TRANSACTION(name), and evaluates to a period.  What was recorded as current on March 1 about Melanie?  The default is SELECT SNAPSHOT Drug FROM Prescription AS P WHERE Name = 'Melanie‘ AND TRANSACTION(P) OVERLAPS DATE '1995­03­01‘ AND VALID(P) OVERLAPS DATE '1995­03­01‘ AND TRANSACTION(...) OVERLAPS CURRENT_TIMESTAMP

Aggregates  SQL­92 supports the aggregates MIN, MAX, COUNT, SUM, and AVG, plus a new temporal aggregate called RISING.  Snapshot reducibility implies that these aggregates return time­varying results when applied to temporal tables.  The aggregate is applied to each snapshot in turn.  Evaluation can be optimized, as many snapshots will contain the same rows, and hence evaluate to the same result.

Aggregates, cont.  How many drugs is/was Melanie taking? SELECT COUNT(*) FROM Prescription WHERE Name = 'Melanie‘ AND Drug = 'Proventil’  How many people are taking each drug? SELECT Drug, COUNT(*) FROM Prescription GROUP BY Drug.  Again, the result is a temporal table.

Discussion  A critique of TSQL2