U-SQL Does SQL (SQLBits 2016)

Michael Rys
Principal Program Manager, Big Data @ Microsoft
@MikeDoesBigData, {mrys, usql}@microsoft.com
U-SQL Does SQL

“Top 5”s
Surprises for SQL
Users
AS is not as
• C# keywords and SQL keywords overlap
• Costly to make case-insensitive -> Better
build capabilities than tinker with syntax
= != ==
• Remember: C# expression language
null IS NOT NULL
• C# nulls are two-valued
PROCEDURES but no WHILE
No UPDATE nor MERGE
• Transform/Recook instead

@customers =
SELECT Customer.ToUpper() AS Customer
FROM @orders
WHERE Customer.Contains("Contoso");
C# Expression
Transforming Rowsets
C# Expression
Use WHERE for filtering

@rows =
SELECT
Customer,
SUM(Amount) AS TotalAmount
FROM @orders
GROUP BY Customer;
Many other aggregations are
possible. You can define
your own aggregator with
C#!
Grouping & Aggregation

@rows =
SELECT
Customer,
SUM(Amount) AS TotalAmount
FROM @orders
GROUP BY Customer
HAVING TotalAmount > 1000000;
HAVING filters the output of
a GROUP BY
Grouping & Aggregation (2)

Sorting a rowset
@customers
SELECT *
FROM @customers
ORDER BY Amount ASC
FETCH FIRST 3 ROWS;
SELECT with ORDER BY
requires a FETCH FIRST!

Sorting on OIUTPUT
OUTPUT @customers
TO @"/output.tsv"
ORDER BY Amount ASC
USING Outputters.Tsv();

Creating Constant Rowsets in Script
@departments =
SELECT * FROM
(VALUES
(31, "Sales"),
(33, "Engineering"),
(34, "Clerical"),
(35, "Marketing")
) AS
D( DepID, DepName );

@m = SELECT new ARRAY<string>(tweet.Split(' ').Where(x => x.StartsWith("@"))) AS refs
FROM @t;
@t = SELECT author, "authored" AS category
FROM @t
UNION ALL
SELECT r.Substring(1) AS r, "referenced" AS category
FROM @m CROSS APPLY EXPLODE(refs) AS Refs(r);
category,
, category
@m(refs)
@me, @you
@him, @her
Refs(r)
@me
@you
@him
@her
@me, @you
@me
@you

U-SQL
Joins
Join operators
• INNER JOIN
• LEFT or RIGHT or FULL OUTER JOIN
• CROSS JOIN
• SEMIJOIN
• equivalent to IN subquery
• ANTISEMIJOIN
• Equivalent to NOT IN subquery
Notes
• ON clause comparisons need to be of the simple form:
rowset.column == rowset.column
or AND conjunctions of the simple equality comparison
• If a comparand is not a column, wrap it into a column in a previous
SELECT
• If the comparison operation is not ==, put it into the WHERE clause
• turn the join into a CROSS JOIN if no equality comparison
Reason: Syntax calls out which joins are efficient

U-SQL
Analytics
Windowing Expression
Window_Function_Call 'OVER' '('
[ Over_Partition_By_Clause ]
[ Order_By_Clause ]
[ Row _Clause ]
')'.
Window_Function_Call :=
Aggregate_Function_Call
| Analytic_Function_Call
| Ranking_Function_Call.
Windowing Aggregate Functions
ANY_VALUE, AVG, COUNT, MAX, MIN, SUM, STDEV, STDEVP, VAR, VARP
Analytics Functions
CUME_DIST, FIRST_VALUE, LAST_VALUE, PERCENTILE_CONT,
PERCENTILE_DISC, PERCENT_RANK; soon: LEAD/LAG
Ranking Functions
DENSE_RANK, NTILE, RANK, ROW_NUMBER

INSERT
• INSERT constant
values
• INSERT from
queries
• Multiple INSERTs
INSERT constant values
INSERT INTO T VALUES (1, "text",
new SQL.MAP<string,string>("key","value"));
INSERT from queries
INSERT INTO T SELECT col1, col2, col3 FROM
@rowset;
Multiple INSERTs into same table
• Is supported
• Generates separate file per insert in physical storage:
• Can lead to performance degradation
• Recommendations:
• Try to avoid small inserts
• Rebuild table after frequent insertions with:
ALTER TABLE T REBUILD;

Additional
Resources
Documentation
U-SQL Reference Doc: http://aka.ms/usql_reference
Sample Projects
https://github.com/Azure/usql/tree/master/Examples/Ambulan
ceDemos/AmbulanceDemos/2-Ambulance-Structured%20Data
https://github.com/Azure/usql/tree/master/Examples/TweetAn
alysis

http://aka.ms/AzureDataLake

U-SQL Does SQL (SQLBits 2016)

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