Use subscript for accessing a dynamic index of an array instead of a udf

The subscript operator in SQL supports full expressions, unlike Hive (which only supports constants). Therefore you can write queries like:

SELECT my_array[CARDINALITY(my_array)] as last_element
FROM ...

Avoid out of bounds access of arrays

Accessing out of bounds elements of an array will result in an exception. You can avoid this with an if as follows:

SELECT IF(CARDINALITY(my_array) >= 3, my_array[3], NULL)
FROM ...

Use ANSI SQL syntax for arrays

Arrays are indexed starting from 1, not from 0:

SELECT my_array[1] AS first_element
FROM ...

Construct arrays with ANSI syntax:

SELECT ARRAY[1, 2, 3] AS my_array

Use ANSI SQL syntax for identifiers and strings

Strings are delimited with single quotes and identifiers are quoted with double quotes, not backquotes:

SELECT name AS "User Name"
FROM "7day_active"
WHERE name = 'foo'

Quote identifiers that start with numbers

Identifiers that start with numbers are not legal in ANSI SQL and must be quoted using double quotes:

SELECT *
FROM "7day_active"

Use the standard string concatenation operator

Use the ANSI SQL string concatenation operator:

SELECT a || b || c
FROM ...

Use standard types for CAST targets

The following standard types are supported for CAST targets:

SELECT
  CAST(x AS varchar)
, CAST(x AS bigint)
, CAST(x AS double)
, CAST(x AS boolean)
FROM ...

In particular, use VARCHAR instead of STRING.

Use CAST when dividing integers

Presto follows the standard behavior of performing integer division when dividing two integers. For example, dividing 7 by 2 will result in 3, not 3.5. To perform floating point division on two integers, cast one of them to a double:

SELECT CAST(5 AS DOUBLE) / 2

Use WITH for complex expressions or queries

When you want to re-use a complex output expression as a filter, use either an inline subquery or factor it out using the WITH clause:

WITH a AS (
  SELECT substr(name, 1, 3) x
  FROM ...
)
SELECT *
FROM a
WHERE x = 'foo'

Use UNNEST to expand arrays and maps

Presto supports UNNEST for expanding arrays and maps. Use UNNEST instead of LATERAL VIEW explode().

Hive query:

SELECT student, score
FROM tests
LATERAL VIEW explode(scores) t AS score;

Presto query:

SELECT student, score
FROM tests
CROSS JOIN UNNEST(scores) AS t (score);

Outer Join Differences

Adhering to the ANSI SQL spec, Presto respects the abstract concept that the whole ON clause is evaluated to determine whether or not a row from the left table will be joined with a right table row. In a LEFT JOIN, all the rows of the left table are always returned out of the join, vice versa for a RIGHT JOIN. In contrast, Hive will first apply any constant filters in the ON clause then perform the join. This can produce very different results when ON clause predicates refer to the outer table.

When you want to convert a Hive OUTER JOIN query to Presto, remember that Hive treats the ON clause predicates as if it were part of the WHERE clause. So to get the equivalent behavior in Presto, you need to move your ON clause predicates into the WHERE clause.

Hive query:

SELECT a.id, b.userid
FROM a
LEFT JOIN b
ON a.id = b.id AND a.ds = '2013-11-11'

Presto query:

SELECT a.id, b.userid
FROM a
LEFT JOIN b
ON a.id = b.id
WHERE a.ds = '2013-11-11'