Expressions

Enterprise Edition

An expression is a language fragment that can be evaluated to return a value. For example, the expression 2 + 3 returns the value 5. Expressions are the building blocks from which queries are constructed. SQL++ supports nearly all of the kinds of expressions in SQL, and adds some new kinds as well.

SQL++ is an orthogonal language, which means that expressions can serve as operands of higher level expressions. By nesting expressions inside other expressions, complex queries can be built up. Any expression can be enclosed in parentheses to establish operator precedence.

In this section, we’ll discuss the various kinds of SQL++ expressions.

Expr

Operator Expressions

Operators perform a specific operation on the input values or expressions. The syntax of an operator expression is as follows:

OperatorExpr

The language provides a full set of operators that you can use within its statements. Here are the categories of operators:

Arithmetic Operators, to perform basic mathematical operations;
Collection Operators, to evaluate expressions on collections or objects;
Comparison Operators, to compare two expressions;
Logical Operators, to combine operators using Boolean logic.

The following table summarizes the precedence order (from higher to lower) of the major unary and binary operators:

Operator	Operation
EXISTS, NOT EXISTS	Collection emptiness testing
^	Exponentiation
*, /, DIV, MOD (%)	Multiplication, division, modulo
+, -	Addition, subtraction
\|\|	String concatenation
IS NULL, IS NOT NULL, IS MISSING, IS NOT MISSING, IS UNKNOWN, IS NOT UNKNOWN, IS VALUED, IS NOT VALUED	Unknown value comparison
BETWEEN, NOT BETWEEN	Range comparison (inclusive on both sides)
=, !=, <>, <, >, <=, >=, LIKE, NOT LIKE, IN, NOT IN	Comparison
NOT	Logical negation
AND	Conjunction
OR	Disjunction

Operator

Operation

EXISTS, NOT EXISTS

Collection emptiness testing

Exponentiation

*, /, DIV, MOD (%)

Multiplication, division, modulo

+, -

Addition, subtraction

String concatenation

IS NULL, IS NOT NULL, IS MISSING, IS NOT MISSING,
IS UNKNOWN, IS NOT UNKNOWN, IS VALUED, IS NOT VALUED

Unknown value comparison

BETWEEN, NOT BETWEEN

Range comparison (inclusive on both sides)

=, !=, <>, <, >, <=, >=, LIKE, NOT LIKE, IN, NOT IN

Comparison

NOT

Logical negation

AND

Conjunction

Disjunction

In general, if any operand evaluates to a MISSING value, the enclosing operator will return MISSING; if none of the operands evaluates to a MISSING value but there is an operand which evaluates to a NULL value, the enclosing operator will return NULL. However, there are a few exceptions listed in comparison operators and logical operators.

Arithmetic Operators

Arithmetic operators are used to exponentiate, add, subtract, multiply, and divide numeric values, or concatenate string values.

Operator Purpose Example

Operator	Purpose	Example
+, -	As unary operators, they denote a positive or negative expression	SELECT VALUE -1;
+, -	As binary operators, they add or subtract	SELECT VALUE 1 + 2;
*	Multiply	SELECT VALUE 4 * 2;
/	Divide (returns a value of type `double` if both operands are integers)	SELECT VALUE 5 / 2;
DIV	Divide (returns an integer value if both operands are integers)	SELECT VALUE 5 DIV 2;
MOD (%)	Modulo	SELECT VALUE 5 % 2;
^	Exponentiation	SELECT VALUE 2^3;
\|\|	String concatenation	SELECT VALUE "ab"\|\|"c"\|\|"d";

+, -

As unary operators, they denote a
positive or negative expression

SELECT VALUE -1;

+, -

As binary operators, they add or subtract

SELECT VALUE 1 + 2;

Multiply

SELECT VALUE 4 * 2;

Divide (returns a value of type double if both operands are integers)

SELECT VALUE 5 / 2;

DIV

Divide (returns an integer value if both operands are integers)

SELECT VALUE 5 DIV 2;

MOD (%)

Modulo

SELECT VALUE 5 % 2;

Exponentiation

SELECT VALUE 2^3;

String concatenation

SELECT VALUE "ab"||"c"||"d";

Collection Operators

Collection operators are used for membership tests (IN, NOT IN) or empty collection tests (EXISTS, NOT EXISTS).

Operator	Purpose	Example
IN	Membership test	FROM customers AS c WHERE c.address.zipcode IN ["02340", "02115"] SELECT *;
NOT IN	Non-membership test	FROM customers AS c WHERE c.address.zipcode NOT IN ["02340", "02115"] SELECT *;
EXISTS	Check whether a collection is not empty	FROM orders AS o WHERE EXISTS o.items SELECT *;
NOT EXISTS	Check whether a collection is empty	FROM orders AS o WHERE NOT EXISTS o.items SELECT *;

Operator

Purpose

Example

Membership test

FROM customers AS c
WHERE c.address.zipcode IN ["02340", "02115"]
SELECT *;

NOT IN

Non-membership test

FROM customers AS c
WHERE c.address.zipcode NOT IN ["02340", "02115"]
SELECT *;

EXISTS

Check whether a collection is not empty

FROM orders AS o
WHERE EXISTS o.items
SELECT *;

NOT EXISTS

Check whether a collection is empty

FROM orders AS o
WHERE NOT EXISTS o.items
SELECT *;

Comparison Operators

Comparison operators are used to compare values.

The comparison operators fall into one of two sub-categories: missing value comparisons and regular value comparisons. SQL++ (and JSON) has two ways of representing missing information in an object — the presence of the field with a NULL for its value (as in SQL), and the absence of the field (which JSON permits). For example, the first of the following objects represents Jack, whose friend is Jill. In the other examples, Jake is friendless à la SQL, with a friend field that is NULL, while Joe is friendless in a more natural (for JSON) way, i.e., by not having a friend field.

Examples

{"name": "Jack", "friend": "Jill"}

{"name": "Jake", "friend": NULL}

{"name": "Joe"}

The following table enumerates all of the comparison operators available in SQL++.

Operator	Purpose	Example
IS NULL	Test if a value is NULL	FROM customers AS c WHERE c.name IS NULL SELECT *;
IS NOT NULL	Test if a value is not NULL	FROM customers AS c WHERE c.name IS NOT NULL SELECT *;
IS MISSING	Test if a value is MISSING	FROM customers AS c WHERE c.name IS MISSING SELECT *;
IS NOT MISSING	Test if a value is not MISSING	FROM customers AS c WHERE c.name IS NOT MISSING SELECT *;
IS UNKNOWN	Test if a value is NULL or MISSING	FROM customers AS c WHERE c.name IS UNKNOWN SELECT *;
IS NOT UNKNOWN	Test if a value is neither NULL nor MISSING	FROM customers AS c WHERE c.name IS NOT UNKNOWN SELECT *;
IS KNOWN (IS VALUED)	Test if a value is neither NULL nor MISSING	FROM customers AS c WHERE c.name IS KNOWN SELECT *;
IS NOT KNOWN (IS NOT VALUED)	Test if a value is NULL or MISSING	FROM customers AS c WHERE c.name IS NOT KNOWN SELECT *;
BETWEEN	Test if a value is between a start value and a end value. The comparison is inclusive of both the start and end values.	FROM customers AS c WHERE c.rating BETWEEN 600 AND 700 SELECT *;
=	Equality test	FROM customers AS c WHERE c.rating = 640 SELECT *;
!=	Inequality test	FROM customers AS c WHERE c.rating != 640 SELECT *;
<>	Inequality test	FROM customers AS c WHERE c.rating <> 640 SELECT *;
<	Less than	FROM customers AS c WHERE c.rating < 640 SELECT *;
>	Greater than	FROM customers AS c WHERE c.rating > 640 SELECT *;
<=	Less than or equal to	FROM customers AS c WHERE c.rating <= 640 SELECT *;
>=	Greater than or equal to	FROM customers AS c WHERE c.rating >= 640 SELECT *;
LIKE	Test if the left side matches a pattern defined on the right side; in the pattern, "%" matches any string while "_" matches any character.	FROM customers AS c WHERE c.name LIKE "%Dodge%" SELECT *;
NOT LIKE	Test if the left side does not match a pattern defined on the right side; in the pattern, "%" matches any string while "_" matches any character.	FROM customers AS c WHERE c.name NOT LIKE "%Dodge%" SELECT *;

Operator

Purpose

Example

IS NULL

Test if a value is NULL

FROM customers AS c
WHERE c.name IS NULL
SELECT *;

IS NOT NULL

Test if a value is not NULL

FROM customers AS c
WHERE c.name IS NOT NULL
SELECT *;

IS MISSING

Test if a value is MISSING

FROM customers AS c
WHERE c.name IS MISSING
SELECT *;

IS NOT MISSING

Test if a value is not MISSING

FROM customers AS c
WHERE c.name IS NOT MISSING
SELECT *;

IS UNKNOWN

Test if a value is NULL or MISSING

FROM customers AS c
WHERE c.name IS UNKNOWN
SELECT *;

IS NOT UNKNOWN

Test if a value is neither NULL nor MISSING

FROM customers AS c
WHERE c.name IS NOT UNKNOWN
SELECT *;

IS KNOWN (IS VALUED)

Test if a value is neither NULL nor MISSING

FROM customers AS c
WHERE c.name IS KNOWN
SELECT *;

IS NOT KNOWN (IS NOT VALUED)

Test if a value is NULL or MISSING

FROM customers AS c
WHERE c.name IS NOT KNOWN
SELECT *;

BETWEEN

Test if a value is between a start value and a end value. The comparison is inclusive of both the start and end values.

FROM customers AS c WHERE c.rating BETWEEN 600 AND 700 SELECT *;

Equality test

FROM customers AS c
WHERE c.rating = 640
SELECT *;

Inequality test

FROM customers AS c
WHERE c.rating != 640
SELECT *;

Inequality test

FROM customers AS c
WHERE c.rating <> 640
SELECT *;

Less than

FROM customers AS c
WHERE c.rating < 640
SELECT *;

Greater than

FROM customers AS c
WHERE c.rating > 640
SELECT *;

Less than or equal to

FROM customers AS c
WHERE c.rating <= 640
SELECT *;

Greater than or equal to

FROM customers AS c
WHERE c.rating >= 640
SELECT *;

Test if the left side matches a pattern defined on the right side; in the pattern, "%" matches any string while "_" matches any character.

FROM customers AS c WHERE c.name LIKE "%Dodge%" SELECT *;

NOT LIKE

Test if the left side does not match a pattern defined on the right side; in the pattern, "%" matches any string while "_" matches any character.

FROM customers AS c WHERE c.name NOT LIKE "%Dodge%" SELECT *;

The following table summarizes how the missing value comparison operators work.

Operator	Non-NULL/Non-MISSING value	NULL value	MISSING value
IS NULL	FALSE	TRUE	MISSING
IS NOT NULL	TRUE	FALSE	MISSING
IS MISSING	FALSE	FALSE	TRUE
IS NOT MISSING	TRUE	TRUE	FALSE
IS UNKNOWN	FALSE	TRUE	TRUE
IS NOT UNKNOWN	TRUE	FALSE	FALSE
IS KNOWN (IS VALUED)	TRUE	FALSE	FALSE
IS NOT KNOWN (IS NOT VALUED)	FALSE	TRUE	TRUE

Operator

Non-NULL/Non-MISSING value

NULL value

MISSING value

IS NULL

FALSE

TRUE

MISSING

IS NOT NULL

TRUE

FALSE

MISSING

IS MISSING

FALSE

TRUE

IS NOT MISSING

TRUE

FALSE

IS UNKNOWN

FALSE

TRUE

IS NOT UNKNOWN

TRUE

FALSE

IS KNOWN (IS VALUED)

TRUE

FALSE

IS NOT KNOWN (IS NOT VALUED)

FALSE

TRUE

Logical Operators

Logical operators perform logical NOT, AND, and OR operations over Boolean values (TRUE and FALSE) plus NULL and MISSING.

Operator	Purpose	Example
NOT	Returns true if the following condition is false, otherwise returns false	SELECT VALUE NOT 1 = 1; Returns FALSE
AND	Returns true if both branches are true, otherwise returns false	SELECT VALUE 1 = 2 AND 1 = 1; Returns FALSE
OR	Returns true if one branch is true, otherwise returns false	SELECT VALUE 1 = 2 OR 1 = 1; Returns TRUE

Operator

Purpose

Example

NOT

Returns true if the following condition is false, otherwise returns false

SELECT VALUE NOT 1 = 1;
Returns FALSE

AND

Returns true if both branches are true, otherwise returns false

SELECT VALUE 1 = 2 AND 1 = 1;
Returns FALSE

Returns true if one branch is true, otherwise returns false

SELECT VALUE 1 = 2 OR 1 = 1;
Returns TRUE

The following table is the truth table for AND and OR.

A	B	A AND B	A OR B
TRUE	TRUE	TRUE	TRUE
TRUE	FALSE	FALSE	TRUE
TRUE	NULL	NULL	TRUE
TRUE	MISSING	MISSING	TRUE
FALSE	FALSE	FALSE	FALSE
FALSE	NULL	FALSE	NULL
FALSE	MISSING	FALSE	MISSING
NULL	NULL	NULL	NULL
NULL	MISSING	MISSING	NULL
MISSING	MISSING	MISSING	MISSING

A AND B

A OR B

TRUE

FALSE

TRUE

NULL

TRUE

MISSING

TRUE

FALSE

NULL

FALSE

NULL

FALSE

MISSING

FALSE

MISSING

NULL

MISSING

NULL

MISSING

The following table demonstrates the results of NOT on all possible inputs.

A	NOT A
TRUE	FALSE
FALSE	TRUE
NULL	NULL
MISSING	MISSING

NOT A

TRUE

FALSE

TRUE

NULL

MISSING

Quantified Expressions

QuantifiedExpr

Synonym for SOME: ANY

Quantified expressions are used for expressing existential or universal predicates involving the elements of a collection.

The following pair of examples illustrate the use of a quantified expression to test that every (or some) element in the set [1, 2, 3] of integers is less than three. The first example yields FALSE and second example yields TRUE.

It is useful to note that if the set were instead the empty set, the first expression would yield TRUE ("every" value in an empty set satisfies the condition) while the second expression would yield FALSE (since there isn’t "some" value, as there are no values in the set, that satisfies the condition).

A quantified expression will return a NULL (or MISSING) if the first expression in it evaluates to NULL (or MISSING). Otherwise, a type error will be raised if the first expression in a quantified expression does not return a collection.

Examples

EVERY x IN [ 1, 2, 3 ] SATISFIES x < 3 -- ➊
SOME x IN [ 1, 2, 3 ] SATISFIES x < 3  -- ➋

➀ Returns FALSE
➁ Returns TRUE

Path Expressions

PathExpr

Components of complex types in the data model are accessed via path expressions. Path access can be applied to the result of a query expression that yields an instance of a complex type, for example, an object or an array instance.

For objects, path access is based on field names, and it accesses the field whose name was specified.

For arrays, path access is based on (zero-based) array-style indexing. Array indices can be used to retrieve either a single element from an array, or a whole subset of an array. Accessing a single element is achieved by providing a single index argument (zero-based element position), while obtaining a subset of an array is achieved by providing the start and end (zero-based) index positions; the returned subset is from position start to position end - 1; the end position argument is optional. If a position argument is negative then the element position is counted from the end of the array (-1 addresses the last element, -2 next to last, and so on).

Multisets have similar behavior to arrays, except for retrieving arbitrary items as the order of items is not fixed in multisets.

Attempts to access non-existent fields or out-of-bound array elements produce the special value MISSING. Type errors will be raised for inappropriate use of a path expression, such as applying a field accessor to a numeric value.

The following examples illustrate field access for an object, index-based element access or subset retrieval of an array, and also a composition thereof.

Examples

({"name": "MyABCs", "array": [ "a", "b", "c"]}).array    -- ➊
(["a", "b", "c"])[2]                                     -- ➋
(["a", "b", "c"])[-1]                                    -- ➌
({"name": "MyABCs", "array": [ "a", "b", "c"]}).array[2] -- ➍
(["a", "b", "c"])[0:2]                                   -- ➎
(["a", "b", "c"])[0:]                                    -- ➏
(["a", "b", "c"])[-2:-1]                                 -- ➐

➀ Returns [["a", "b", "c"]]
➁ Returns ["c"]
➂ Returns ["c"]
➃ Returns ["c"]
➄ Returns [["a", "b"]]
➅ Returns [["a", "b", "c"]]
➆ Returns [["b"]]

Primary Expressions

PrimaryExpr

The most basic building block for any expression in SQL++ is Primary Expression. This can be a simple literal (constant) value, a reference to a query variable that is in scope, a parenthesized expression, a function call, or a newly constructed instance of the data model (such as a newly constructed object, array, or multiset of data model instances).

Literals

Literal

The simplest kind of expression is a literal that directly represents a value in JSON format. Here are some examples:

-42
"Hello"
true
false
null

Numeric literals may include a sign and an optional decimal point. They may also be written in exponential notation, like this:

5e2
-4.73E-2

String literals may be enclosed in either single quotes or double quotes. Inside a string literal, the delimiter character for that string must be "escaped" by a backward slash, as in these examples:

"I read \"War and Peace\" today."
'I don\'t believe everything I read.'

The table below shows how to escape characters in SQL++.

Character Name Escape Method

Character Name	Escape Method
Single Quote	`\'`
Double Quote	`\"`
Backslash	`\\`
Slash	`\/`
Backspace	`\b`
Formfeed	`\f`
Newline	`\n`
CarriageReturn	`\r`
EscapeTab	`\t`

Single Quote

\'

Double Quote

\"

Backslash

\\

Slash

\/

Backspace

\b

Formfeed

\f

Newline

\n

CarriageReturn

\r

EscapeTab

\t

Identifiers and Variable References

Like SQL, SQL++ makes use of a language construct called an identifier. An identifier starts with an alphabetic character or the underscore character _ , and contains only case-sensitive alphabetic characters, numeric digits, or the special characters _ and $. It is also possible for an identifier to include other special characters, or to be the same as a reserved word, by enclosing the identifier in back-ticks (it’s then called a delimited identifier). Identifiers are used in variable names and in certain other places in SQL++ syntax, such as in path expressions, which we’ll discuss soon. Here are some examples of identifiers:

X
customer_name
`SELECT`
`spaces in here`
`@&#`

A very simple kind of SQL++ expression is a variable, which is simply an identifier. As in SQL, a variable can be bound to a value, which may be an input dataset, some intermediate result during processing of a query, or the final result of a query. We’ll learn more about variables when we discuss queries.

Note that the SQL++ rules for delimiting strings and identifiers are different from the SQL rules. In SQL, strings are always enclosed in single quotes, and double quotes are used for delimited identifiers.

Parameter References

A parameter reference is an external variable. Its value is provided using the statement execution API.

Parameter references come in two forms, Named Parameter References and Positional Parameter References.

Named parameter references consist of the "$" symbol followed by an identifier or delimited identifier.

Positional parameter references can be either a "$" symbol followed by one or more digits or a "?" symbol. If numbered, positional parameters start at 1. "?" parameters are interpreted as $1 to $N based on the order in which they appear in the statement.

Parameter references may appear as shown in the below examples:

Examples

$id
$1
?

An error will be raised in the parameter is not bound at query execution time.

Parenthesized Expressions

ParenthesizedExpr

Subquery

An expression can be parenthesized to control the precedence order or otherwise clarify a query. A subquery (nested selection) may also be enclosed in parentheses. For more on these topics please see their respective sections.

The following expression evaluates to the value 2.

Example

( 1 + 1 )

Function Calls

FunctionCall

OrdinaryFunctionCall

AggregateFunctionCall

ScopeName

Functions are included in SQL++, like most languages, as a way to package useful functionality or to componentize complicated or reusable computations. A function call is a legal query expression that represents the value resulting from the evaluation of its body expression with the given parameter bindings; the parameter value bindings can themselves be any expressions in SQL++.

Note that Window functions, and aggregate functions used as window functions, have a more complex syntax. Window function calls are described in the section on Window Queries.

Also note that FILTER expressions can only be specified when calling Aggregation Pseudo-Functions.

The following example is a function call expression whose value is 8.

Example

length('a string')

Case Expressions

CaseExpr

SimpleCaseExpr

SearchedCaseExpr

In a simple CASE expression, the query evaluator searches for the first WHEN … THEN pair in which the WHEN expression is equal to the expression following CASE and returns the expression following THEN. If none of the WHEN … THEN pairs meet this condition, and an ELSE branch exists, it returns the ELSE expression. Otherwise, NULL is returned.

In a searched CASE expression, the query evaluator searches from left to right until it finds a WHEN expression that is evaluated to TRUE, and then returns its corresponding THEN expression. If no condition is found to be TRUE, and an ELSE branch exists, it returns the ELSE expression. Otherwise, it returns NULL.

The following example illustrates the form of a case expression.

Example

CASE (2 < 3) WHEN true THEN "yes" ELSE "no" END

Constructors

Constructor

ObjectConstructor

ArrayConstructor

MultisetConstructor

Structured JSON values can be represented by constructors, as in these examples:

{ "name": "Bill", "age": 42 } -- ➊
[ 1, 2, "Hello", null ]       -- ➋

➀ An object
➁ An array

In a constructed object, the names of the fields must be strings (either literal strings or computed strings), and an object may not contain any duplicate names. Of course, structured literals can be nested, as in this example:

[ {"name": "Bill",
   "address":
      {"street": "25 Main St.",
       "city": "Cincinnati, OH"
      }
  },
  {"name": "Mary",
   "address":
      {"street": "107 Market St.",
       "city": "St. Louis, MO"
      }
   }
]

The array items in an array constructor, and the field-names and field-values in an object constructor, may be represented by expressions. For example, suppose that the variables firstname, lastname, salary, and bonus are bound to appropriate values. Then structured values might be constructed by the following expressions:

An object:

{
  "name": firstname || " " || lastname,
  "income": salary + bonus
}

An array:

["1984", lastname, salary + bonus, null]

If only one expression is specified instead of the field-name/field-value pair in an object constructor then this expression is supposed to provide the field value. The field name is then automatically generated based on the kind of the value expression as in Q2.1:

If it is a variable reference expression then the generated field name is the name of that variable.
If it is a field access expression then the generated field name is the last identifier in that expression.
For all other cases, a compilation error will be raised.

Example

(Q2.1)

FROM customers AS c
WHERE c.custid = "C47"
SELECT VALUE {c.name, c.rating}

This query outputs:

[
    {
        "name": "S. Logan",
        "rating": 625
    }
]